Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Title: Blueprint Food Microbiology
Description: This document contains elaborate study materials of Food Microbiology course for both Bachelor's and Masters level. All the topics covered those taught at various prestigious institutions all over the world. It covers all the books listed in the “Booklist” section. The most easy-to-understand topics are selected from various textbooks and screenshots from those books are added as well. Total page: 66.
Description: This document contains elaborate study materials of Food Microbiology course for both Bachelor's and Masters level. All the topics covered those taught at various prestigious institutions all over the world. It covers all the books listed in the “Booklist” section. The most easy-to-understand topics are selected from various textbooks and screenshots from those books are added as well. Total page: 66.
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
Food
Microbiology
Book list
1
...
Jay
2
...
Banwart
3
...
Food Microbiology: Fundamentals and Frontiers (4th Edition)
ASM press
5
...
Food and Microorganisms
Food microbiology: Food microbiology is the study of microorganisms that inhibit, create or contaminate food
...
Food: Food is any substance consumed to provide nutritional support for an organism
...
The substance is
ingested by an organism and assimilated by the organisms’ cells to provide energy, maintain life or stimulate growth
...
2
...
Perishable: This kind of foods spoil quickly within few days
...
Perishable foods include dairy products, meat, poultry, fish
...
g
...
Non-perishable: This kind of foods have very long shelf life such as months or years, e
...
canned fruits and
vegetables, dried fruits and vegetables, peanut butter
...
The key requirements for chilled food products are good quality and microbiological safety at the point
of consumption
...
Food and Fish Spoilage and Prevention
Food spoilage: Food spoilage means the original nutritional value, texture, flavor of the food are damaged, the food
become harmful to people and unsuitable to eat
...
Various external forces are responsible for the
spoilage of food
...
Causes of spoilage
1
...
3
...
5
...
7
...
MEAL IP TT
Microorganisms
Enzymes
Air
Light
Insects, parasites, rodents
Physical damage
Temperature
Time
They are discussed below:
1
...
The microorganisms that can
cause food-borne illness are called pathogenic microorganisms
...
Pathogenic microorganisms
may grow in foods without any noticeable change in color, odor, appearance or taste
...
When spoilage microorganisms are present, the food usually looks and/or smells awful
...
Enzymes: Enzymes, substances naturally present in food, are responsible for the ripening process in fruits and
vegetables
...
For example, as a banana turns from
green to yellow to brown, not only does the color change, but there is also a change in the fruit’s texture
...
Air: Oxidation, a chemical process that produces undesirable change in color, flavor and nutrient content,
results when air reacts with food components
...
Discoloration of light colored fruits can be reduced by using an antioxidant, such as ascorbic acid or citric acid,
before freezing
...
4
...
Light also may be responsible for the oxidation
of fats
...
Insects, parasites and rodents:
• Insects destroy –
o Fruits and vegetables by not only consuming the food but contaminating the food
...
• Parasites enter the human body mostly through poultry which have been improperly cooked
...
Rodents are also carriers of pathogenic bacteria
...
Physical damage: Bruises and cracks on raw produce leave areas where microorganisms easily may grow
...
7
...
Microorganisms, both spoilage and pathogenic, grow rapidly at room temperature
...
8
...
Other reactions, such as oxidation and enzyme action,
also require time to develop
...
These parameters are as follows:
PM NOAB
3
1
...
3
...
5
...
pH
Moisture content
Oxidation reduction potential (Eh)
Nutrient content
Antimicrobial constituents
Biological structure
They are discussed below:
1
...
3
...
5
...
pH: Adverse pH affects at least two aspects of a respiring microbial cell: the functioning of its enzymes and
the transport of nutrients into the cell
...
Moisture content: One of the oldest methods of preserving foods is drying
...
It is
not generally accepted that the water requirements of microorganisms should be described in terms of the water
activity (aw) in the environment
...
Reduction is the gain of electrons or a decrease in oxidation state by a molecule atom
or ion
...
Nutrient content: In order to grow and function normally, the microorganisms of importance in foods require
the following:
• Water
• Source of energy
• Source of nitrogen
• Vitamins and related growth factors
• Minerals
Antimicrobial constituents: Cow’s milk contains several antimicrobial substances, including lactoferrin,
conglutinin and the lactoperoxidase system
...
Milk casein as well as some free
fatty acids have been shown to be antimicrobial under certain conditions
...
Biological structure: The natural covering of some foods provides excellent protection against the entry and
subsequent damage by spoilage organisms
...
In the case of nuts such as pecans
and walnuts, the shell of covering is sufficient to prevent the entry of all organisms
...
They are those properties of the
environment that affect both the foods and their microorganisms
...
2
...
4
...
Temperature: Microorganisms, individually and as a group, grow over a very wide range of temperatures
...
The lowest temperature at which a microorganism has been reported to grow is – 340 C; the highest is
somewhere in excess of 1000 C
...
2
...
3
...
It
along with O2 are the two most important gases in modified atmosphere packaged foods
...
Ozone (O3) is the other atmospheric gas that has antimicrobial properties and it has been tried over a
number of decades as an agent to extend the shelf life of certain foods
...
Ozone was tested against E
...
Presence and activities of other microorganisms: Some foodborne organisms produce substances that are either
inhibitory or lethal to others
...
The inhibitory effect of some members of the food biota on others is well established
...
Chemical changes begin automatically after fruits and vegetables are harvested or animals are killed (slaughtered)
...
Chemical
changes affect the color and flavor of foods; fats and pigments in foods are mainly affected e
...
unpleasant smell and
taste of cooking oil after use at high temperature
...
2
...
Lipid autolysis: Enzymatic hydrolysis with fatty acids and glycerol as main product is called lipid autolysis
...
Oxidative rancidity in fish
can result to serious quality problems such as rancid falvours and odors as well as discoloration
...
The
most common chemical action which causes spoilage is the oxidative rancidity in fatty fishes
...
Autolytic spoilage: Every living organism uses specialized proteins called enzymes to drive the chemical reactions in
its cells
...
For example, some enzymes in a tomato help it to ripen, but other
enzymes cause it to decay
...
Autolytic spoilage is caused by enzymes
...
This process is known as Rigor Mortis
...
The enzymes present in muscle convert glycogen into lactic acid
...
After the composition of rigor mortis, muscle stiffness gradually decreases accompanied by increases in
pH, ending up in softening of muscle
...
This process is called
autolysis
...
When fruits or vegetables are peeled or cut, the plant tissue releases some enzymes which in the presence of O2 from
the air, chemically react with plant compounds to give brown pigments e
...
apple, banana, guava etc
...
The red pigment in meat undergoes chemical changes and turns brown when it is
exposed to O2
...
Starch changes to sugar,
color changes and texture softens
...
Food preservation
Food processing: Food processing is the set of methods and techniques used to transform raw ingredients into food or
to transform food into other forms for consumption by humans or animals either in the home or by the food processing
industry
...
Importance of food preservation:
Food preservation helps in –
1
...
Increasing the shelf-life of foods and thus increasing the supply
...
Making the seasonal food available throughout the year
...
4
...
6
...
Adding variety to the diet
...
Stabilizing prices of food, as there is less scope of shortage of supply to demand
...
Improving the nutrition of the population
...
Principles of food preservation:
A good method of food preservation is one that slows down or prevents altogether the action of the agents of spoilage
...
The principles of food preservations
are:
1
...
3
...
For the preservation
of green leafy vegetables, the water should be removed from the leaves so that microorganisms cannot survive
...
Inactivating enzymes: Enzymes found in food can be inactivated by changing their conditions such as
temperature and moisture
...
This method inactivates enzymes and thus, the food
...
Methods of food preservation: There are two techniques of food preservation
...
Traditional techniques and
B
...
Traditional techniques of food preservation:
1
...
Cooling
3
...
Boiling
5
...
Sugaring
7
...
Lye (sodium hydroxide)
9
...
Jellying
11
...
Burial
13
...
2
...
Curing: Curing is any of various food preservation and flavouring processes of foods such as meat,
fish, fruit and vegetables, by addition of combinations of salt, nitrites or sugar, with the aim of drawing
moisture out of the food by the process of osmosis
...
Dehydration was the earliest form of
food curing
...
Cooling: Cooling preserves food by slowing down the growth and reproduction of microorganisms
and the action of enzymes that causes the food to rot
...
Freezing: Freezing is also one of the most commonly used processes, both commercially and
domestically, for preserving a very wide range of foods, including prepared foods that would not have
6
required freezing in their unprepared state
...
Cold stores provide large volume, long term storage for strategic food stocks held in case of national
emergency in many countries
...
Boiling: Boiling of liquid food items can kill any existing microbes
...
5
...
Milk is also boiled before storing to kill many microorganisms
...
Sugaring: The earliest cultures have used sugar as a preservative and it was common place to store
fruit in honey
...
In northern climates without sufficient sun to dry foods, preserves are made by heating the food with
sugar
...
This process leaves the microbial
cells dehydrated, thus killing them
...
Sugar is used to preserve fruits, either
in an antimicrobial syrup with fruit such as apples, pears, peaches, apricots and plums, or in
crystallized form where the preserved material is cooked in sugar to the point of crystallization and
the resultant product is then stored dry
...
7
...
Pickling can be
broadly classified into two categories: chemical pickling and fermentation pickling
...
Typical pickling agents include brine (high in salt), vinegar, alcohol and vegetable
oil
...
• Fermentation pickling: Bacteria in the liquid produce organic acids as preservation agents, typically
by a process that produces lactic acid through the presence of lactobacillales
...
8
...
Lye
will saponify fats in the food, which will change its falvour and texture
...
9
...
It was invented by French
confectioner Nicolas Appert
...
Although Appert had discovered a new way of preservation, it wasn’t understood until 1864 when
Louis Pasteur found the relationship between microorganisms, food spoilage and illness
...
Jellying: Food may be preserved by cooking in a material that solidifies to forma gel
...
Jellied eels are a delicacy in the East End of London, where they are eaten with mashed potatoes
...
Many jugged meats are also jellied
...
Jugging: Meat can be preserved by jugging
...
The animal to be jugged is usually cut into pieces, placed into a tightly sealed jug with brine or gravy
and stewed
...
Jugging was a popular method of preservation meat up until the middle of the 20th century
...
Burial: Burial of food can preserve it due to a variety of factors:
o lack of light
o lack of O2
o Cool temperatures
o pH level
o desiccants in the soil
Burial may be combined with other methods such as salting or fermentation
...
Cabbage was traditionally
buried during Autumn in northern US farms for preservation
...
Fermentation: Fermentation is the microbial conversion of starch and sugars into alcohol
...
Fermentation
can also make foods more nutritious and palatable
...
These microorganisms keep pathogens in check by creating an
environment toxic for themselves and other microorganisms by producing acid or alcohol
...
Modern industrial techniques for food preservation:
1
...
Vacuum packing
Pressure এ Plasma Modify আে Biopreservation
3
...
Irradiation
করে Pulse হাোয়
5
...
Modified atmosphere
7
...
High pressure food preservation
9
...
Hurdle technology
They are discussed below:
1
...
Pasteurization kills vegetative bacteria but not spores
...
↓
Cooled quickly below 100 C
↓
It is packed in bottle, carton or container
...
2
...
4
...
Vacuum packing: Vacuum packing stores food in a vacuum environment usually in an air tight bag or bottle
...
Vacuum packing is commonly used for
storing nuts to reduce loss of flavor from oxidization
...
Artificial food additives: Preservative food additives can be antimicrobial – which inhibit the growth of
bacteria or fungi, including mold or antioxidant, such as O 2 absorbers, which inhibit the oxidation of food
constituents
...
) and EDTA
...
Other
preservatives include formaldehyde (usually in solution), glutaraldehyde (insecticide), ethanol and
methylchloroisothiazolinone
...
The two types of ionizing
radiation used are beta particles (high energy electrons) and gamma rays (emitted from radioactive sources
such as cobalt-60 or cesium-137)
...
Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries
...
Pulsed electric field electroporation: Pulsed electric field (PEF) electroporation is a method for processing
cells by means of brief pulses of a strong electric field
...
8
In PEF processing, a substance is placed between two electrodes, then the pulsed electric field is applied
...
PEF for food processing is a developing technology still being researched
...
6
...
Salad crops that are notoriously difficult to preserve are now being packaged in sealed bags with an
atmosphere modified to reduce the O2 concentration and increase the CO2 concentration
...
There are two methods for preserving grains with CO2
...
Another method is purging the container
from the bottom by gaseous CO2 from a cylinder or bulk supply vessel
...
Grain
stored in this way can remain edible for approximately 5 years
...
7
...
This causes microorganisms to die off on the surface
...
High pressure food preservation: High pressure food preservation or pascalization refers to the use of a food
preservation technique that makes use of high pressure
...
9
...
Beneficial bacteria or the fermentation products produced by these
bacteria are used in biopreservation to control spoilage and render pathogens inactive in food
...
LAB have antagonistic properties that make them particularly
useful as biopreservatives
...
Some LAB produce the antimicrobial nisin, which is
a particularly effective preservative
...
Using them in combination
with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can
inhibit the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria
...
Hurdle technology: Hurdle technology is a method of ensuring that pathogens in food products can be
eliminated or controlled by combining more than one approach
...
The right combination
of hurdles can ensure that all pathogens are eliminated or rendered harmless in the final product
...
2
...
4
...
Microorganisms should not be able to jump over all the hurdles present in the food product
...
The hurdle concept illustrates that complex interactions of temperature, water activity, pH etc
...
Types of hurdles: There are more than 60 potential hurdles those can be used for food preservation, but the
most important hurdles used are:
•
•
•
•
•
•
Temperature (both high and low)
Water activity
Acidity (pH)
Redox potential (Eh)
Chemical preservatives
Competitive microorganisms
Mechanism of food preservation by Hurdle Technology:
9
•
•
•
•
Homeostasis: The homeostasis of microorganisms plays a key role in food preservation
...
Therefore, food preservation can be achieved by disrupting the homeostasis of microorganisms,
temporarily or permanently
...
As a response to the hurdles applied to foods, microorganisms try to
repair their homeostasis, use up all their energy for this and become metabolically exhausted
...
The foods which are preserved with the concept of hurdle
technology and are microbiologically stable, become safer during storage at ambient temperature
...
Stress reactions: As a response to various hurdles e
...
heat, pH, Aw, ethanol, oxidative compounds
etc
...
These stress proteins
may hamper food preservation and could turn out to be problematic for the application of hurdle
technology if only one hurdle has been applied
...
Synthesis of many stress shock proteins
due to simultaneous exposure to different stresses will be very energy-consuming and would lead to
metabolic exhaustion of the microorganism
...
g
...
This disturbs the homeostasis of the microorganisms present in several respects
...
Therefore, simultaneous application of different hurdles in a particular food would lead to
optimal microbial stability
...
2
...
4
...
6
...
Saves money, energy and several other resources
...
Does not affect the integrity of food pieces (fruits)
...
Manufacture of new products according to the need of processors and consumers
...
Fish
spoilage can be caused by the breakdown of biomolecules like protein, amino acid and fats that are naturally found in
the fish
...
In chemical degradation, protein, fats,
amino acids etc
...
Other than bacterial and chemical degradation, enzymatic and mechanical damage are also type of spoilage
...
The microorganisms involved in fish spoilage are referred to as SSOs (Specific Spoilage Organisms) which results in
numerous unwanted metabolites being produced in the food cause undesirable appearance, flavor and odor
...
Definition: Fish spoilage can be defined as the contamination of fish, which results in the undesirable change in the
color, odor, texture and appearance
...
Fish spoilage can occur as a result of enzymatic degradation, bacterial degradation, chemical decomposition and
mechanical damage
...
Action of enzymes: Various autolytic enzymes causes spoilage of fish after death
...
Conversion of ATP to hypoxanthine: This conversion adds bitter taste, and we can estimate the
degree of freshness by knowing the hypoxanthine content
...
2
...
When a fish gets died, the bacteria
already present in the fish attacks the flesh and result in the formation of undesirable products
...
The bacteria cause fish spoilage by:
• Reducing TMAO to TMA: Reduction of trimethylamine oxide into trimethylamine produces an
offensive odor
...
Example:
3
...
5
...
7
...
1
...
Glutamic-acid → Arginine
• Degradation of urea to ammonia: It also produces an offensive odor
...
High fat content: Fish which have high fat content, are prone to spoilage rapidly
...
Weak muscle tissue: Bacteria can attack easily weak muscles
...
Ambient temperature: Most bacteria grow in an ambient temperature
...
Unhygienic handling: Unhygienic handling causes spoilage because it provides bacteria a favorable
environment to attack and grow
...
The spoilage process starts immediately after death of fish
...
2
...
Rigor mortis
Autolysis
Bacterial invasion and putrefaction
They are discussed below:
1
...
Rigor mortis: The rigor mortis is a physical effect on the muscle tissue of fish caused by chemical changes
following the death
...
After the death, the normal circulatory system breaks down and chemical signals leak into the muscle causing
them to stiffen
...
Autolysis: After the completion of rigor mortis, muscle stiffness gradually decreases accompanied by increase
in pH, ending up in softening of muscle
...
This process
is called autolysis
...
Conversion of ATP to hypoxanthine: This conversion adds bitter taste, and we can estimate the
degree of freshness by knowing the hypoxanthine content
...
11
3
...
When a
fish gets died, the bacteria already present in the fish attacks the flesh and result in the formation of undesirable
products
...
The bacteria
cause fish spoilage by:
• Reducing TMAO to TMA: Reduction of trimethylamine oxide into trimethylamine produces an
offensive odor
...
Example:
•
o Histidine → Histamine
o Glutamic-acid → Arginine
Degradation of urea to ammonia: It also produces an offensive odor
...
2
...
4
...
Bacteria, because of their shorter generation time, are in a favourable position over moulds to cause rapid
spoilage of foods
...
The initial microbial load and the percentage of spoilage bacteria in it decide the shelf life of any product
...
Fish is a highly perishable food which need proper handling and preservation if it is to have a long shelf life and retain
a desirable quality and nutritional value
...
Fish preservation techniques: Preservation techniques are needed to prevent fish spoilage and lengthen shelf life
...
Preservation techniques can be classified as follows:
1
...
3
...
5
...
Control of temperature
Control of water activity
Physical control of microbial loads
Chemical control of microbial loads
Control of O2 reduction potential
Combined techniques
They are discussed below:
1
...
Control of temperature: If the temperature is decreased, the metabolic activity in the fish from microbial or
autolytic processes can be reduced or stopped
...
On fishing vessels, the fish are refrigerated mechanically by circulating cold air or by packing the fish in boxes
with ice
...
It is a safe cooling method that keeps the fish moist and in an easily stored form suitable for transport
...
It ranges between 0 and 1 and is a parameter that
measures how available the water is in the flesh of the fish
...
There are a number of techniques that have been or are used to tie up the available water or remove it by
reducing the aw
...
These techniques can be very simple, for example, by using solar drying
...
Often a combination of these techniques is used
...
4
...
6
...
Heat is applied by cooking, blanching or microwave heating in a manner that pasteurizes or
sterilizes fish products
...
Sterilized products are
stable at ambient temperatures up to 400 C, but to ensure that they remain sterilized, they need packaging in
metal cans before the heat treatment
...
Biopreservation is achieved by adding antimicrobials or by increasing the acidity of the
fish muscle
...
5
...
Lactic acid bacteria produce the antimicrobial
nisin which further enhances preservation
...
Control of the O2 reduction potential: Spoilage bacteria and lipid oxidation usually need O 2, so reducing the
O2 around fish can increase shelf life
...
Controlled or modified atmosphere have specific combinations of O 2, CO2 and N2
...
Combined techniques: Two or more of these techniques are often combined
...
Other process
combinations are being developed along multiple hurdle theory
...
B
...
D
...
Physical method
Subjective method
Organoleptic method
Chemical method
Biological method
They are discussed below:
A
...
From the digital readings or values of Torrymeter, we can estimate the
freshness of fish
...
10 is the highest value for the
freshly caught fish, and below 3 is the value of spoiled fish
...
B
...
C
...
We can check the quality of fish by a sense of sight by seeing the eyes, gills and skin surface like:
• The eyes should be clear and vibrant
...
• The gills should be red-pink in color
...
• The skin or surface of the fish should be clear and there must not be any discoloration
...
The scales should be intact with the skin
...
There should not be fishy, sour or ammonia-like smell
...
Chemical method: It includes the following methods:
• Proximate testing: It is a prevalent method, in which the fish components like moisture, protein, lipid
etc
...
This method does not give a satisfactory
assessment and thus is not accepted
...
The value of hypoxanthine increases during the storage of fish
...
A fish is considered to be spoiled when
the hypoxanthine value reaches 7 – 8 micromoles g⸺1
...
The value of TMA with a level of
1
...
• Ammonia production: The production of ammonia indicates that there is an extent of spoilage
...
Peroxidase value < 10 indicates the
good quality of fish, but the value > 20 indicates rancidity
...
TBA value < 2, is
accepted by the customer
...
Biological method: It includes total plate count method (TPC), which is used in the quality assessment of fish
by giving an estimate of bacterial presence
...
↓
Media is prepared for the growth of microorganisms present in the fish, where both ordinary and
selective media are used
...
Other than this, selective media like SS agar can be used for the
detection of coliform bacteria (Salmonella, Shigella, E
...
↓
Pouring method is performed
↓
The plates are incubated for 24 hours at 35 – 370 C
...
↓
Total plate count method thus gives a count for the bacterial population present in the fish, which can
be pathogenic and non-pathogenic
...
Meat
Sources of contamination: The important contamination comes from external sources during bleeding, handling and
processing
...
2
...
4
...
6
...
During handling of meat: Boxes, containers, air and other contaminated meat
...
In the market: Knives, saws, cleavers, slicers, grinders, chopping blocks, scales and containers
...
Growth of organisms on surface, touching the meats and on the meat themselves increases their numbers
...
So,
the preservation of meats is done by combination of preservative methods
...
2
...
But this
may lessen the nutrients and damage color
...
• Heat applied during the smoking of meats and its products helps to reduce microbial numbers
...
• Chilling: Modern packing house methods involve chilling meat immediately and rapidly to
temperature near freezing
...
Time limit of chilling is depending upon microbial load and vary according to animal
...
2 to
⸺28
...
The freezing process kills about half of the bacteria and number decreases slowly during storage
...
4
...
Use of irradiation: Irradiation with UV rays has been in conjunction with chilling storage to lengthen the
keeping time
...
Irradiation has been used in the rapid aging of meats that are hung at higher than the usual chilling
temperatures to reduce the growth of organisms on the surface
...
Preservation by drying: Meat for drying should be of good bacteriological quality to avoid undesirable flavor
...
Drying may be done by vacuum technique in trays
...
The curing agents permitted are: NaCl, sugar and
nitrate
...
Its main purpose is to low the aw (water activity)
...
Sucrose is chiefly used and glucose is used as a substitute
...
Methods of introduction of curing agents to meat:
15
i
...
iii
...
The dry cure: Dry ingredients are rubbed into the meat
...
The injection cure: A concentrated solution of the ingredients is injected by a needle into arteries of
the meat
...
The direct addition method: The curing agents are added directly to finely ground meats
...
• To aid in preservation
...
Drying of the meat, together with chemicals from the smoke, inhibits microbial growth
during storage
...
8
...
For
example, bologna, polish, frankfurter and other sausages owe their keeping quality to the combined effect of
spicing, curing, smoking, cooking and refrigerating
...
The most often recommended antibiotics are chloretetracycline and chloramphenicol
...
The antibiotic may be fed to the animal over a long period
...
It may be fed to more intensively for a short period before slaughter
...
It may be infused into the carcass or its part of it
...
It may be applied to the surface of meat or mixed with continued meat
...
The storage life of meats could be lengthen by
the means of antibiotics
...
2
...
4
...
6
...
The physical properties of meat: The amount of exposed surface of the flesh influence on the rate of spoilage
...
Availability of O2: Aerobic conditions at the surface of meat are favourable for yeasts, molds and aerobic
bacteria
...
e
...
The method of killing and bleeding: The better sanitary the bleeding, better would be the keeping quality of
meat
...
Spoilage under aerobic conditions
B
...
Spoilage under aerobic conditions: Under aerobic conditions, bacteria may cause the following:
1
...
16
2
...
4
...
6
...
g
...
Lactobacillus and Leuconostoc are basically responsible
...
g
...
Pseudomonas and Achromobacter are
responsible for oxidative rancidity or by yeast
...
g
...
They grow on the surface of meat
...
• Yellow pigments: Produced by the species of Micrococcus or Flavobacterium
...
• Purple ‘stamping ink’ discoloration of surface fat: Caused by Yellow pigmented cocci and
rods
...
Souring is the term applied to
almost any defect that gives the sour odor that may be due to volatile acids e
...
formic acid,
butyric acid, propionic acid
...
Actinomycetes are responsible for
musty or earthy flavor
...
• Actinomycetes may cause musty or earthy flavour
...
Aerobic growth of molds on meat: Aerobic growth of molds may cause –
1
...
3
...
5
...
Sickness: Surface becomes sticky
...
Black spot: It is usually caused by Clostridium herbarum
...
Green patches: It is caused by Penicillium species such as P
...
oxalicum
...
B
...
The terminology used in connection with this spoilage is:
1
...
This could be caused by formic, acetic, butyric, propionic and
higher fatty acids or other organic acids like lactic acid
...
Acid and gas formation
accompany the action of the butyric Clostridium species and the coliform bacteria on carbohydrates
...
• Anaerobic production of fatty acids or lactic acid during ripening
...
2
...
It is usually caused by Clostridium species
...
chiefly in the
genera Pseudomonas and Alcaligens
...
Trimethyl amine in fish and isovalenic acid in butter are described as putrid
odors
...
Taint: This word is implied to any off-taste, off-odor
...
True putrefiers require temperature above those of refrigerator
...
2
...
4
...
Form small intracellular ice crystals
...
Ice crystals do not damage food cells because
too small to rupture the cells
...
2
...
4
...
Form large extracellular ice crystals
...
Ice crystals damage the food cells causing loss of
texture, nutrients, color and flavor on thawing
...
In fish
• Acinatobacter
• Alcaligenes
• E
...
In meat
• Pseudomonas
• Bacillus
• E
...
In milk
• Lactic acid bacteria
4
...
These
changes can be like change in appearance, color, odor, taste etc
...
Factors affecting the growth of microorganisms in milk:
1
...
3
...
Milk sugar: The only sugar naturally present in milk is lactose
...
Lactic acid
bacteria which do have lactase readily break down lactose and use glucose as an energy source
...
Further, some lactic acid bacteria are able to convert galactose to
glucose
...
8 which serves as a good growth medium for
bacteria
...
Moisture: Milk has a high moisture content (typically 87% for cows’ milk) and with respect to available
moisture, is an excellent growth medium
...
Milk acquire some dissolved O2 during milking,
storage and handling
...
18
5
...
7
...
The
temperature of raw milk is nearly room temperature
...
Time: Microorganisms need time to grow and multiply
...
So, if milk is left unpasteurized for a long time, then microbes become to grow
...
Types of microorganisms in milk:
A
...
Temperature characteristic types and
C
...
Biochemical types: It consists of organisms that bring biochemical changes in the milk
...
• Souring of milk: It includes microorganisms that embitter the taste of milk
...
Signs of spoilage: Sour milk, curd formation etc
...
Examples: Bacillus, Proteus, Micrococcus
...
• Gas production: It includes microorganisms that produce acid and gas mainly coliforms; cause
stormy fermentation of milk
...
Examples: Clostridium, Bacillus, Coliform
...
• Ropiness: It includes microorganisms that make the milk highly viscous, sticky and characteristic silklike thread appears
...
It is of two types: surface
ropiness and ropiness throughout the milk
...
• Color changes in milk: It results from prolonged storage of milk
...
Examples:
1
...
3
...
Yellow milk: It is caused by Flavibacterium
...
Yeast may produce red or pink colonies on the
surface of sour milk
...
Brown milk: It is caused by Pseudomonas putrifaciens
...
Examples: Penicillium, Geotrichum
...
B
...
Examples: Flavobacterium, Pseudomonas, Coliforms
...
• Mesophilic bacteria: These grow at temperature between 25 – 400 C
...
o Streptococcus lactis: Malty and caramel taint
...
19
•
•
Thermophilic bacteria: It is defined as heat-loving bacteria which grow at a temperature between 55
– 650 C
...
Changes in milk: Off flavor and odor
...
It can result from faulty cleaning and improper handling and survive at pasteurization
temperature but cannot grow
...
C
...
Diseases can be transmitted either through raw milk, cow or others
...
o Bacillus anthracis causes anthrax in both cow and man
...
Microbial examination of milk: It can be done by the following methods:
A
...
It gives a rough and direct assessment of a viable number of bacteria that is a very simple
method to carry out
...
e
...
↓
Then solid agar media is transferred on sterile plate
...
5 ml of a sample is spread onto the plate
...
Interpretation of the result: More than 300 colonies indicates that the milk is unpotable
...
e
...
B
...
It is used to examine
the presence of coliform bacteria that cause the fermentation of milk by the production of acid and gas
...
Procedure:
Firstly, MacConkey colony fluid medium is taken
...
↓
After that, Durham tube is dipped and incubated for 24 – 48 hours at 35 – 370 C
...
Negative: If there is no acid and gas formation
...
Methylene blue reductase test: It is the quickest method to determine the microbial load
...
A speed of reduction of methylene blue color is directly
proportional to the volume of bacteria present in the milk sample
...
Procedure: A definite quantity of methylene blue is added to 10 mL of milk
...
Interpretation of the result:
De-coloration time
Result
30 min ⸺ 2 hours
Poor quality
2 ⸺ 6 hours
Fair quality
6 ⸺ 8 hours
Good quality
Over 8 hours
Best quality
Shorter the discoloration time, higher is the volume of bacterial flora present in the milk and poor is the quality
and vice versa
...
Resazurin test: It is very similar to the methylene blue reductase test
...
Interpretation of the result:
Positive: Formation of pink color indicates the presence of bacteria that reduce resazurin
...
e
...
E
...
It verifies whether milk is pasteurized or not
...
This enzyme gets inactivated if pasteurization is
performed properly
...
↓
A few drops of sodium biphenyl phosphate is added
...
Interpretation of the result:
Positive: Blue color appears, indicating the presence of phosphatase (milk is pasteurized
appropriately)
...
F
...
It milk is sterilized properly, then all coagulable heat proteins get
precipitated
...
22
↓
Then a few drops of ammonium sulfate is added
...
Interpretation of the result:
Positive: If turbidity appears, milk is not sterilized properly
...
G
...
It counts both viable and non-viable cells
...
01 mL of raw milk is taken in glass slide (hemocytometer) and then air dried
...
↓
Bacterial clumps is counted in a colony counter
...
Bitter flavour: This results from proteolysis, fermentation of lactose, lipolysis
...
Burnt or caramel flavour: This is caused by Streptococcus lactis
...
coli
• Fruit flavour is caused by Pseudomonas fragi
• Potato like flavour is caused by Pseudomonas mucidolens
...
Yellow milk: It is caused by Flavibacterium
...
Yeast may produce red or pink colonies on the surface of sour
milk
...
Cheese production:
Cheese production is the largest dairy industry in the world
...
Types: Broadly two types:
1
...
Unripened cheese: Cottage cheese with low fat, cream cheese with high fat
...
g
...
g
...
Production process
All cheese are irreversibly made from casein of milk that is
produced after separating the whey (liquid protein of milk)
...
g
...
The production process of cheese is discussed hereunder:
1
...
3
...
Acidification of milk: By employing lactic acid bacteria
(Streptococcus lactis, Lactobacillus lactis) the sugar of milk
(lactose) can be converted to lactic acid
...
6 and thus acidifies milk
...
e
...
Casein mainly
consists of three components – insoluble α and ꞵ-caseins
and a κ casein that keeps them in soluble state
...
Consequently,
α and ꞵ-caseins and the degraded products of κ casein combine to form a coagulum (curd)
...
Separation of curd from whey: When the temperature of the coagulum is raised to around 400C, the coagulum
(curd) and whey (fluid portion) get separated
...
Ripening of cheese: The flavour of raw cheese (with rubber texture) such as cheddar is bland
...
The procedures adopted for ripening (or maturation) are highly
variable depending on the type of cheese to be prepared
...
Alternatively, they may be inoculated with certain fungi (e
...
Penicillium
roquefortii)
...
Mild hydrolysis of fats (or cheese), usually carried out by
lipases or Aspergillus niger or Mucor maihai results in butyric acid formation with characteristic flavour
...
While L
...
thermophilus results in the
formation of lactic acid to give acid flavour
...
Yogurt is very delicious and in fact, frozen yoghurt is becoming popular
as an alternative to ice cream
...
2
...
Adjustment of milk composition and blending ingredients: Milk composition may be adjusted to achieve
desired fat and solids content
...
Pasteurization of milk: Milk is pasteurized at 850 C for 30 minutes or at 950 C for 10 minutes
...
Homogenization: The blend is homogenized (2,000 – 2,500 psi) to mix all ingredients thoroughly and improve
yogurt consistency
...
5
...
7
...
Cooling milk: The milk is cooled to 420 C to bring the yogurt to the ideal growth temperature for the starter
culture
...
Holding: The milk is held at 420 C until a pH of 4
...
Cooling: The yogurt is then cooled to 70 C to stop the fermentation
...
25
3
...
Food poisoning
is a foodborne disease characterized by symptoms:
•
•
•
•
Nausea
Vomiting
Abdominal cramping and
Diarrhea that occur suddenly (within 48 hours) after consuming a contaminated food or drink
...
All food
poisonings are foodborne diseases, but all foodborne diseases are not food poisoning
...
These
symptoms may affect one person or a group of persons who ate the same thing (called an outbreak)
...
Foodborne infections vs intoxication:
1
...
3
...
Cause
Invasion or
multiplication
Incubation
period
Destruction
6
...
Foodborne infections
This is the foodborne illness caused by
the entrance of microorganisms into
body
through
ingestion
of
contaminated food/drinks and their
reactions of the body to their presence
and metabolites
...
Hours to days
Foodborne intoxication
This is the foodborne illness caused by
presence of toxins in food
...
Cannot be destroyed by cooking or freezing
(exception is toxin produced by C
...
Inadequate cooking, improper handling
temperatures
...
Foodborne disease
Foodborne disease is any disease resulting from
contamination of food by pathogenic bacteria,
viruses or parasites as well as chemicals or
natural toxins such as poisonous mushrooms
...
3
...
5
...
Usually one person gets affected
...
1
...
3
...
5
...
Caused by toxins (these toxins can be produced
by microorganisms, can occur naturally in the
food or can be a contaminant)
...
Not self-limited
...
Classification of food borne diseases: On the basis of mode of illnesses, food borne diseases can be divided into the
following types:
A
...
A toxin has to be present in the contaminated food
...
Examples:
1
...
Botulism
3
...
Infection: Illness occurs as a result of the consumption of the food and water contaminated with
enteropathogenic bacteria or viruses
...
Viable cells, even if present in small numbers, have the potential
to establish and multiply in the digestive tract to cause illness
...
Salmonellosis
2
...
Yersiniosis
4
...
coli
5
...
coli colitis
6
...
Shigellosis
8
...
Vibrio vulnificus infection
10
...
Viral infections
C
...
Generally, the bacterial cells either sporulate or die and release toxins
to produce the symptoms
...
Clostridium perfringens gastroenteritis
2
...
E
...
Cholera
[Fundamental Food Microbiology by Bibek Ray]
Sequence of events in a foodborne disease:
Initially, there has to be a source of pathogen
↓
Next, the pathogen has to contaminate a food
...
↓
For bacterial pathogens (and toxicogenic molds) the contaminated food has to support growth and be exposed
for a certain period of time at a suitable temperature to enable the pathogens to grow
...
coli O157:H7), growth may not be necessary to cause a foodborne infection
...
• For bacterial infection, viable cells of a pathogen need to be consumed in sufficient numbers, which
vary greatly with pathogens, to survive stomach acidity, establish in the digestive tract and cause
illness
...
27
Host invasion:
UNIVERSAL requirements
There are several hurdles that an intestinal pathogen must overcome in order to cause illness:
1
...
3
...
5
...
Some pathogens are aided
in this process by the protective effect of food and some survive acidity by the use of their adaptive acid
tolerance mechanisms
...
The mucous
layer that covers the intestinal mucosa is regarded as being the first line of defense encountered by enteric
pathogens
...
With a pathogen such as C
...
It must possess the capacity to defend itself against host defense mechanisms such as gut – associated lymphoid
tissue
...
This is the gist of competitive
exclusion in that the harmless biota, once attached to all available sites on the intestinal walls, will exclude
pathogens
...
Once attached, the organisms need to be able to either elaborate toxic products (e
...
Vibrio cholerae non 01) or
cross the epithelial wall and enter pathogenic or somatic cells (e
...
L
...
28
Food related diseases caused by Bacillus species
B
...
2
...
4
...
6
...
Temperature for growth: Optimum 300 C, minimum 100 C, maximum 500 C
...
9 – 9
...
7 – 3
...
Its spores possess a resistance to heat typical of other mesophiles
...
• In a study of raw meats, meat products and product additives, B
...
6% of 534,
18
...
1% of 609 samples respectively, with levels of 102 – 104 /g
...
cereus must be ingested to develop sings and symptoms
...
2
...
4
...
6
...
It has a molecular weight of 55kDa and apparently plays no role in the foodborne gastroenteritis syndromes
...
A
...
Emetic syndrome
They are discussed below:
A
...
2
...
Toxin involved: Enterotoxin which is heat labile and sensitive to trypsin and pepsin
...
The toxin responsible for diarrheal syndrome are formed in the
small intestine of the host
...
3
...
4
...
5
...
6
...
Duration of illness is generally
12 – 24 hours
...
Emetic syndrome:
Characteristics:
1
...
It is heat stable at 1260 C for 90 minutes
...
Structure of the toxin: The compound is named cereulide
...
6
...
2
...
3
...
4
...
5 to 5 hours
...
5
...
Using the S
...
The 5-HT3 receptor antagonist,
ondansetron, also abolished Cereulide-induced vomiting in Suncus
...
Using rat liver mitochondria, Mahler et al showed
that emetic toxin inhibited electron transport and uncoupled oxidative phosphorylation
...
Many European countries report ifs implication as food borne disease
...
2
...
4
...
Chilling foods rapidly in small quantities
...
Practice personal hygiene
...
Reheating left over foods to 71
...
Food related diseases caused by Staphylococcus species
The staphylococcal food poisoning or food intoxication syndrome was first studied in 1894 by J
...
Some authors
refer to food associated illness of this type as food intoxication rather than food poisoning
...
2
...
4
...
6
...
Appear in grape like clusters due to incomplete three planer divisions
...
Produce golden yellow colony in solid media (e
...
nutrient agar)
...
e
...
Colonies are pin head sized and surrounded by β hemolysis
...
aureus contains three main components:
• The peptidoglycan comprising repeating units of N-acetyl glucosamine β-1,4 glucosamine linked to
N-acetyl muramic acid
...
• Protein A which is covalently linked to the peptidoglycan and particularly is characterized by its ability
to bind to Fc component of the immunoglobulin in plasma causing autoagglutination
...
Catalase positive, ferment mannitol and can grow in media containing high salt concentration (10-20% NaCl)
...
Toxin:
S
...
The most important toxins are called
Staphylococcal enterotoxins (SEs)
...
In
addition, the SEC has three antigenically distinct subtypes: SEC1, SEC2, SEC3 and SEG have a virulent form called
SEGv
...
SEs
are a heterogenous group of water soluble single chain globular proteins with molecular weight of about 26 – 35 kDa
...
30
Properties of SEs:
1
...
3
...
5
...
7
...
The SEs are generally heat resistant and a heat denatured enterotoxin can be renatured by prolonged storage
or in presence of urea
...
In mushroom, they are stable at 1210 C for 28 minutes
...
It is a 27
...
SEB is a 31
...
SEB
is also resistant to gastrointestinal proteolytic enzymes such as chymotrypsin and trypsin
...
SED (24 kDa) is the second most serotypes responsible for food poisoning
...
The genes for enterotoxin production are located either in a bacteriophage, chromosome or in plasmids
...
The sed and sej genes are co-localized and the same strain always produces these two
toxins (SED and SEJ) together
...
There are five staphylococcal PAI: SaPI-1, SaPI-2, SaPI-3, SaPI-4 and SaPI-bov
...
Production of enterotoxins is not restricted to S
...
Enterotoxins are expressed differentially and the toxin production depends on the growth phase of
bacteria, bacterial density, pH and CO2 levels
...
Foods involved:
•
•
•
•
•
•
•
•
•
Creamy food prepared with milk
Deli foods
Custard (pudding)
Salad dressing
Meats
Hams
Fish
Shellfish and
Milk products
Generally, the enterotoxins are produced at 10 – 460 C
...
Disease or Pathogenicity
1
...
aureus
...
aureus grows in carbohydrate and protein foods
(for example, egg salad, cream pastry)
...
As the enterotoxin is preformed in foods, the incubation period is short
...
aureus in carbohydrate and protein containing foods
↓
Enterotoxin is produced
...
31
↓
Enterotoxin acts as a super antigen and stimulates the release of IL-1 and IL-2 from macrophage and helper T
cells within GIT
...
Clinical features:
1
...
Vomiting
3
...
Rapid convalescence
...
There is no fever
...
Microscopic examination:
Gram staining: Gram positive cocci arranged in grape like irregular clusters
...
Isolation and identification from culture: Culture is done in –
• Blood agar media
• Nutrient agar media
• 5 – 10% NaCl agar
Finding:
• S
...
• S
...
saprophyticus typically yield white colonies that are non-hemolytic
...
2
...
4
...
aureus
Positive
Positive
Positive
Can ferment
S
...
saprophyticus
Positive
Negative
Negative
Cannot ferment
C
...
epidermidis is sensitive, whereas S
...
D
...
Detection of anti-teichoic antibody may
be done
...
Prevention of contamination of food with staphylococci which may be achieved by –
• Adding general methods of sanitation
• By using ingredients free from contamination e
...
pasteurized milk rather than raw milk
...
2
...
Killing staphylococci in food by –
• Pasteurization of food such as custard filled puffs
• Heating for 30 minutes at 191 – 2180 C oven temperature
...
2
...
4
...
6
...
8
...
It is a motile, spore forming Gram-positive rod and spores are located sub-terminally
...
The totulinum neurotoxin is produced at temperatures as low as 3 – 150 C
...
pH: >4
...
Spores are highly resistant to heat and the decimal reduction time is 0
...
8 minutes at 110 – 1210 C
...
9 – 4
...
Foods involved:
•
•
•
•
•
•
•
•
Home-canned vegetables: Beans, peppers, carrots, corn, asparagus, potatoes and fish are implicated in
outbreaks
...
Yogurt
Cream cheese
Canned chilly
Jarred peanuts
Condiments: Sautéed onions, garlic in oil, commercial cheese sauce
...
33
Condiment: A condiment is a spice, sauce, or preparation that is added to food, typically after cooking, to
impart a specific flavor, to enhance the flavor, or to complement the dish
...
When these foods are canned or vacuumpacked without adequate sterilization, spores survive and germinate in the anaerobic environment
...
Toxins:
Types:
A
...
Type A: Commonly cause human botulism in western part of USA
...
2
...
3
...
4
...
5
...
It is found in soil, sea and lake mud
...
6
...
7
...
It is isolated from soil in Argentina
...
On the basis of proteolytic activity:
1
...
2
...
The proteolytic activity of type G is slower than that for type A and its toxin requires trypsin potentiation
...
ii
...
iv
...
Group II: Contains type B, E and F
...
Group IV: Contains serological type G
...
botulinum causes the disease called botulism
...
Toxin is responsible for the disease
...
Lethal
dose of human is about 1 – 2 µg/kg
...
The toxin is rather a neurotoxin which inhibits release of acetylcholine at the synapse resulting in lack of
muscle contraction and paralysis
...
Clinical features:
1
...
Symptoms begin 18-24 hours after ingestion of the toxic food
...
This leads to the following symptoms:
• Visual disturbances e
...
double vision
...
• Speech difficulty
...
• Death occurs from respiratory paralysis or cardiac arrest
...
There is no fever
...
The patient remains fully conscious until shortly before death
...
Types: 4 special clinical forms occur:
1
...
Spore
germination may take place in colon but Clostridia are unable to survive because of the resident microflora
...
Oral administration of toxin is lethal in adult
humans
...
botulinum in the food
...
botulinum in the food
...
↓
The toxin reaches in neuromuscular junction target via the bloodstream
...
Gastrointestinal symptoms (e
...
nausea, dry mouth, diarrhea) are not
regularly prominent
...
• The damage to the synapse once the toxin has bound is permanent, and recovery requires growth
of presynaptic axons and formation of new synapses
...
Wound botulism: Spore contaminate a wound, germinate and produce toxin at the site
...
g
...
The incubation period for wound botulism is 4 – 14
days
...
↓
Anaerobic environment created by tissue destruction and the growth of aerobic bacteria help
germination and growth of Clostridium
...
3
...
The organism is apparently on weaning or with dietary supplements, especially
honey
...
In infant, the spores germinate in the intestinal tract and the
vegetative cells colonize in the gut
...
Symptoms are very similar to adult botulism; however, nausea and vomiting are
absent
...
e
...
Constipation, tachycardia and dry mouth are due to blockage of
parasympathetic nerve impulses
...
Overall mortality rate is 5%
...
4
...
Hidden botulism is neither food related, wound associated nor drug use related
...
Antibiotic treatment due to other
illnesses may disturb natural microflora balance in the gut, thus allowing Clostridium to colonize and produce
toxins
...
C
...
barati produces toxin F which is responsible for hidden botulism in adults
...
e
...
Hidden botulism is diagnosed by
isolation and identification of the Clostridium cells from feces
...
Trivalent antitoxin (types A, B and E): Obtained from horse serum
...
Respiratory support, particularly mechanical ventilation (most important)
...
Antibiotics in wound botulism
...
2
...
4
...
Heating food at 1000 C for 10 minutes before eating destroys the toxin
...
botulinum toxin
...
Clostridium perfringens
Distribution of Clostridium perfringens
The food poisoning strains of C
...
C
...
Because it is a spore former, it can withstand the adverse environmental conditions of
drying, heating and certain toxic compounds
...
2
...
perfringens is a Gram-positive, rod-shaped, spore forming anaerobic but somewhat aerotolerant bacteria
...
The clear zone is produced by
perfringolysin O (theta-toxin) and the hazy outer zone is by phospholipase C (alpha toxin)
...
C
...
4
...
5
...
5 – 8
...
6
...
97 and 0
...
93 with glycerol employing a fluid thioglycollate base
...
Foods involved:
•
•
•
•
Dishes: Prepared in one day and eaten in the next
...
Fish plate
Cold chicken
Toxins:
a
...
perfringens
...
Alpha toxin: It is the most important toxin produced by all stains of C
...
The largest
volumes of alpha toxin are provided by C
...
• The alpha toxin is a lecithinase, a phospholipase C, which in the presence of Ca 2+ and
Mg2+ ions, breaks down lecithin into phosphoribosyl choline and diglyceride
...
• It lethal, dermonecrotic and hemolytic
...
The toxin lyses erythrocytes, leukocytes, platelets and endothelial
cells
...
The toxin is relatively heat stable and is partially inactivated
by boiling for 5 minutes
...
2
...
3
...
This toxin increases
vascular permeability of the wall of gastrointestinal tract
...
b
...
Iota toxin: The iota toxin is a lethal toxin, which produces necrotic lesions and increases vascular
permeability
...
1
...
red blood cells
...
Theta toxin: Theta toxin is an oxygen-labile hemolysin and is a cytolytic toxin
...
Kappa toxin: Kappa toxin is a collagenase
...
Lambda toxin: Lambda toxin is a proteinase and gelatinase
...
Mu toxin: Mu toxin is a hyaluronidase
...
Nu toxin: Nu toxin is a deoxyribonuclease
...
perfringens
...
The toxin is produced during the stage of sporulation of vegetative cells to form spores, which is
stimulated by alkaline environments of the small intestine
...
This causes disruption in transport of ions in the ileum and jejunum and
alters permeability of the membrane
...
Disease:
1
...
3
...
perfringens causes infection, not intoxication
...
Raw foods or ingredients
may be contaminated with spores
...
Also, room temperature storage after cooking allows vegetative cells to grow and multiply
...
↓
The cytotoxic effect of CPE (Clostridium perfringens enterotoxin) starts with binding of the toxin to the 21 kDa
claudin receptor of tight junction (TJ) proteins and the complex then binds to a 45 – 50 kDa membrane protein
forming a complex of 90 kDa referred to as CPE complex
...
CPE also modulates
the architecture of epithelial tight junctions (TJ) by forming a complex with TJ protein occludin and forms a
large complex of 200 kDa
...
↓
As a result, CPE alters the paracellular membrane permeability and contribute to the onset of diarrhea
...
↓
These changes affect the fluid and electrolyte transport, decrease the intestinal absorptive capacity and increase
the stool mass
...
CPE at high concentration (10 μg ml⸺1) induces necrosis (oncosis), which may
contribute to the inflammatory process that is evident during infection
...
Necrotic enteritis is
primarily caused by certain strains of C
...
The necrotizing β toxin acts on autonomic nervous system causing arterial constriction leading
37
to mucosal necrosis
...
Additionally, the α toxin with the phospholipase and sphingomyelinase
activity is also responsible for necrotizing effects
...
Conditions necessary for an outbreak: The following conditions are necessary for an outbreak:
1
...
3
...
5
...
perfringens
...
The food is inadequately cooled and favourable temperature and enough time is allowed for appreciable
growth
...
The cells sporulate in vivo and elaborate the enterotoxin
...
2
...
4
...
Holding hot foods above 600 C
...
Food related diseases caused by E
...
Gram staining property: E
...
2
...
• Most strains are fimbricated or piliated
...
3
...
E
...
5
...
Oxidase negative
7
...
coli
...
Specific serotypes are associated with certain diseases e
...
O55 and O111 cause outbreaks of neonatal diarrhea
...
coli (in short)
1
...
3
...
5
...
• Heat labile toxin (LT)
• Heat stable toxin (ST)
• Verotoxin
Pili: They help the bacteria to adhere to the site of infection
...
Endotoxin
Verotoxn: Shigella-like toxin (SLT)
...
coli:
1
...
The reservoir of E
...
The source of E
...
3
...
coli that causes neonatal meningitis is the mother’s birth canal; the infection is acquired duing
birth
...
In contrast, the E
...
5
...
coli O157 is cattle and the organism is acquired in undercooked
meat
...
coli
...
The genus specific somatic O polysaccharide
b
...
Lipid A
E
...
H or flagellar antigen
b
...
K or capsular antigen and
d
...
b
...
H or flagellar antigen: The H antigens are heat and alcohol labile proteins present on the flagella
...
All of the H antigens are present
as monophasic, but very rarely as diphasic
...
O or somatic antigens: O antigens occur on the surface of the outer membranes and are determined by specific
sugar sequences on the cell surface
...
It is
heat stable, resistant to boiling up to 2 hours and 30 minutes
...
up to 173) O antigens
have been described
...
• The o antigen also sows cross reaction with individual E
...
The O antigens are detected by
agglutination with specific antibodies
...
• K antigen encloses the O antigen and may interfere with detection of the O antigens
...
• K antigens may also contribute to virulence by inhibiting phagocytosis
...
A total of 103 K antigens have been recognized
...
E
...
39
d
...
A number of
filamentous protein structures resembling fimbriae have been described in E
...
These are K88, K99 antigens
in E
...
coli
(ETEC) causing diarrhea in humans
...
Antigenic typing: The serotyping of E
...
E
...
Each O group is then
further divided into subgroups on the basis of K antigens
...
The antigenic pattern of a strains is recorded depending on the number of the particular antigen it carries
(e
...
E
...
Different serotypes of E
...
• The normal colon strains belong to the early O groups (1, 2, 3, 4, etc
...
Diseases caused by E
...
coli causes diseases both within and outside the enteric tract
...
Urinary tract infections (UTI): Cystitis, pyelonephritis (by certain O serotype)
2
...
• Neonatal meningitis
...
• Biliary tract infection
...
Intestinal tract infections: Diarrhea, dysentery
...
coli: Diarrhea causing E
...
Enteropathogenic E
...
Enterotoxigenic E
...
Enteroinvasive E
...
Enterohemorrhagic E
...
coli (VTEC)
E
...
coli (EAEC)
F
...
coli (DAEC)
They are discussed below:
A
...
coli (EPEC):
Disease: Diarrhea in infants
...
Reservoir of infection: Infant cases and adult carriers
...
Infecting dose: Low for infants and very high for adults (108 to 1010 bacteria)
...
The
combination of these actions is called the attachment and effacing (A/E) lesion
...
B
...
coli (ETEC):
Diseases:
1
...
Diarrhea in infants in developing countries
40
Mode of infection: Transmission is by consumption of food and water contaminated by infected human or
convalescent carriers
...
Pathogenesis:
Adherence of ETEC to epithelial cells of the small bowel by pili
↓
Some strains of ETEC produce a heat labile exotoxin (LT)
↓
LT has two subunits: A (for action) and B (for binding)
↓
B subunit binds to the ganglioside receptor of the brush border of the intestinal epithelium
...
↓
Some strains of ETEC produce the heat stable enterotoxin (STa)
...
This stimulates fluid secretion
...
C
...
coli (EIEC): EIEC strains are closely resemble Shigellae in many ways:
• They are non-motile
...
These strains show cross reactivity with O antigen of Shigellae
...
coli strains were named
earlier Shigella alkalescens under the alkalescens-Disper Group (resembling Shigella flexneri except in
fermenting dulcitol and forming alkali in litmus milk) and Shigella dispar (late lactose fermenter like Shigella
sonnei but indole positive)
...
The EIEC strains have
the ability to invade and destroy the colonic epithelium, producing a disease characterized initially by
watery diarrhea
...
coli to invade cells is determined by a large plasmid, which codes for
outer membrane antigens called the virulence marker antigens (VMA)
...
This continuous process of epithelial cell destruction with inflammatory
infiltration leads to the development of ulcers in intestine
...
D
...
coli (EHEC) or verotoxin producing E
...
Bloody diarrhea
2
...
Hemolytic uremic syndrome
Reservoir and source of infection: Gut of herbivores
...
Ingestion of undercooked hamburger, often at fast-food restaurants, unpasteurized juices and fresh
vegetables
...
Direct contact with animals e
...
visits to farms and petting zoos, have resulted in bloody diarrhea
caused by O157:H7 strains
...
Pathogenesis: Shiga toxin acts by removing an adenine from the large (28S) rRNA, thereby stopping protein
synthesis
...
E
...
coli (EAEC): EAEC strains are so called because they show a typical ‘stacked brick’
arrangement on Hep-2 cells or glass due to their autoagglutination
...
These EAEC strains
secrete a low molecular weight, heat stable enterotoxin called enteroaggregative heat stable enterotoxin-1
(EAST-1)
...
This layer of biofilm traps the bacteria in epithelium of the small intestine
...
These strains are associated
with persistent, watery diarrhea with dehydration in infants, especially in developing countries
...
Diffusely adherent E
...
These strains are identified by their ability to adhere to cultured cells
...
Pathogenesis of UTI caused by E
...
coli is the most common cause of UTI and accounts for approximately 90%
of first UTI in young women
...
E
...
Urinary catheters or obstruction
to urine outflow (enlarged prostate) allow the bacteria more time to multiply and cause injury
...
coli preferentially cause UTI
...
↓
The motility of E
...
↓
Once established, LPS, α-hemolysin and cytotoxic necrotizing factor (CNF) cause injury
...
Laboratory diagnosis of UTI or diarrhea caused by E
...
Immunological tests and some others tests are also helpful
...
Specimen collection:
• Freshly passed stool
• Rectal swab
• Urine
B
...
Finding: Gram-negative rods are found
...
Isolation and identification from culture:
1
...
EMB agar media: E
...
D
...
E
...
coli O157:H7 does not ferment sorbitol, which serves as an important criterion that distinguishes it
from other strains of E
...
• For ETEC, EPEC, VTEC done in reference lab
...
Demonstration of toxins of diarrheagenic E
...
coli can be made by demonstration of the bacilli in feces by culture
...
↓
The fecal samples are inoculated directly on MacConkey and blood agar media
...
coli is present as commensals in the intestine, hence is detected even in normal stool; it is
essential to perform various diagnostic tests in order to consider it as diarrheagenic pathogenic E
...
These strains are identified by:
• Serotyping
• Animal inoculation
• Cytopathic effects in cell cultures
• Molecular methods
Food related diseases caused by Salmonella species
Characteristics
1
...
3
...
5
...
7
...
They are Gram negative and motile rod-shaped organisms
...
The primary habitat of Salmonella species is the intestinal tract of animals such as birds, reptiles, farm animals,
humans and occasionally insects
...
As intestinal forms, the organisms are excreted in feces from which they may be transmitted by insects and
other living creatures to a large number of places
...
7 ⸺ 45
...
pH: 4
...
93 – 0
...
06-11
...
The
following sources are important:
•
•
Water: Contamination with feces often results in explosive epidemics
...
Some outbreaks are traceable to the source of supply
...
Dried or frozen eggs: From infected fowl or contaminated during processing
...
Recreational drugs: Marijuana and other drugs
...
g
...
Household pets: Turtles, dogs, cats etc
...
typhi, it may be as few as 103)
...
Gastroenteritis is inflammation of the stomach and intestines, typically resulting from
bacterial toxins or viral infection and causing vomiting and diarrhoea
...
↓
M cells and dendritic cells located in the lamia propia ingest luminal microbiota to maintain homeostasis; a
process which allows Salmonella to cross the epithelial barrier
...
SILTs are composed of isolated lymphoid follicles (ILF) that contain B cells and M cells
...
↓
In the lamia propia, Salmonellae are engulfed by resident dendritic cells or macrophages and replicate inside
host cells or induce apoptosis
...
↓
Massive neutrophil infiltration occurs within 1 – 3 h of infection
...
↓
LPS-invaded inflammation is seen during invasion
...
Inflammation and damage to mucosal cells cause diarrhea and fluid loss
...
Conditions necessary for outbreaks:
44
1
...
3
...
Bacterial count must be high
...
Prevention of outbreak: The main particles involved in the prevention of outbreak are 1
...
3
...
5
...
7
...
Destruction of the organism in food by heat by cooking or pasteurization
...
Prevention of growth of Salmonella in foods by adequate refrigeration or by other means
...
Food handlers should be kept away from food
...
Inspection of animals and meat at the time packing should be done
...
2
...
4
...
V
...
They measure 1 – 3 μm in length
and 0
...
8 μm in diameter
...
S shaped or spiral forms may be seen due to two or more cells lying
end to end
...
In a stained film of mucous flakes from a case of cholera, the
vibrios are typically arranged in parallel rows, described by Koch as the ‘fish in stream’ appearance
...
They show typical darting type motility
and appear as a ‘swarm of gnats’ when examined under the microscope
...
Virulence factors: Virulence factors of V
...
Cholera toxin
2
...
Adhesin factor or accessory colonization factor
4
...
Neuraminidase and
6
...
2
...
Cholera toxin: Cholera toxin is an exotoxin and the most important virulence factor produced by V
...
It is also known as choleragen or cholera enterotoxin; it is structurally and functionally similar to the heat
labile enterotoxin of E
...
It contains two subunits – A and B
...
Cholera toxin has the following
biological functions:
• It inhibits the absorption capacity and activates the excretory chloride transport in the intestinal
enterocytes, eventually leading to loss of NaCl in the intestinal lumen
...
The diarrheic fluid is osmotic in nature but contains much more of
potassium and bicarbonate
...
• It also increases skin capillary permeability
...
Toxin coregulated pilus: The pili help in adherence of V
...
Adhesion factor or accessory colonization factor: These also help in adhesion of bacteria to the intestinal
mucosa
...
5
...
Hemagglutination protease: This enzyme, formerly known as cholera lectin is both agglutinin and zincdependent protease
...
It includes
intestinal inflammation and also helps in releasing free vibrios from the bound mucosa to the intestinal lumen
...
cholerae
...
Foods involved:
•
•
•
•
Seafood
Fish
Shellfish
Bivalve shellfish such as clams, oysters etc
...
For colonization to occur, large number of bacteria (approximately 1 billion)
must be ingested because the organism is particularly sensitive to stomach acid
...
cholerae is transmitted by ingestion of faecally contaminated water or food
...
↓
Secretion of bacterial enzyme mucinase
↓
Mucinase dissolves the protective glycoprotein coating over the intestinal cells
...
↓
After adhering, the organism secretes an enterotoxin called choleragen, which consists of an A (active) subunit
and a B (binding) subunit
...
↓
Increased secretion of Cl⸺ and H2O from the cells
...
↓
Morbidity and death are due to dehydration and electrolyte imbalance
...
Q
...
The organisms secrete an enterotoxin called choleragen which increases secretion
of Cl⸺ and H2O from the cells
...
This is why, the diarrhea in cholera is watery and non-bloody
...
The organism has been characterized as Vibrio cholerae O139 Bengal
...
The epidemic has continued to spread and Vibrio cholerae O139 Bengal
has affected at least 11 countries in Southern Asia
...
During an epidemic, a clinical judgement is
made and there is little need for the laboratory
...
cholerae by microscopic examination
...
Biochemical and serological tests are also helpful
...
Specimen collection:
• Stool
• Vomit
• Rectal swab
First day:
B
...
• Hanging drop preparation: Typical motility (a fish in steam appearance)
...
C
...
• TCBS agar: Large yellow colored colony
...
• MacConkey agar: Colorless colonies, because lactose is fermented slowly
...
Biochemical tests: The organism is oxidase positive, which distinguishes it from members of the
Enterobacteriaceae
...
Serological tests:
• Slide agglutination test (mostly used): Diagnosis can be confirmed by agglutination of the organism
by polyvalent O1 and non-O1 antiserum
...
Food related diseases caused by Campylobacter jejuni
Characteristics:
1
...
3
...
5
...
7
...
9
...
The one of primary importance in foods is C
...
In
addition to C
...
coli, C
...
C
...
Can grow at 420 C
...
It is microaerophilic
...
It is oxidase and catalase positive and can reduce nitrates
...
jejuni differs from C
...
It is resistant to cephalothin
...
jejuni has the distinction of being the first foodborne
...
This organism is also found in vegetables, shellfish and water
...
Unpasteurized milk
...
Vegetables
Shellfish
47
Transmission:
•
There is a low level of transmission between flocks
...
The consensus seems to be that this organism
is not transmitted through the hatchery, but instead to broiler chicks by vermin
...
In addition to poultry, the other primary source of this organism is raw milk
...
Human to human transmission also occurs, but is very rare
...
jejuni produce a heat labile enterotoxin that shares some common properties with
the enterotoxins of V
...
coli (LT)
...
jejuni enteritis appear to be caused in part by the
invasive abilities of the organism
...
Infective dose: 500 – 10,000 organisms (dose often correlates with the intensity of the attack)
...
jejuni: Following three mechanisms have been postulated in the pathogenesis of
intestinal disease caused by C
...
2
...
Adherence and production of heat labile enterotoxins: C
...
Adherence to epithelial cells and/or mucus at these sites is possibly facilitated by flagella
...
PEB1 is a superficial antigen that has been
found to be a major adhesion protein, which is found among C
...
Furthermore, C
...
Invasion and proliferation of bacteria within the intestinal epithelium: C
...
The organism produces diffuse,
bloody, edematous and exudative enteritis
...
It is also
associated with crypt abscesses in the epithelial glands and ulceration of the mucosal epithelium
...
Invasion of intestinal mucosa and proliferation: C
...
This results in extraintestinal infections, such as cholecystitis,
mesentery adenitis, urinary tract infection and meningitis
...
Characteristics:
1
...
3
...
5
...
Campylobacter enteritis is considered to be the leading foodborne
illness in the United States and its prevalence is compared to that of Salmonella and E
...
Prevention:
1
...
V
...
enterocolitica and C
...
Campylobacteriosis can be avoided by not eating undercooked or unpasteurized foods of animal origin,
especially milk
...
2
...
4
...
6
...
8
...
10
...
12
...
Food stored at improper temperature
...
Not washing hands before eating or preparing food
...
Eating raw shellfish
...
Ingestion of expired food
...
Not washing food thoroughly before preparation
...
Unpasteurized foods
...
Among all illnesses caused by food
borne pathogens, recent estimates of as 67% have been attributed to viruses alone, and an upward trend in the
transmission of viruses by food and water has been recently acknowledged
...
It is often called the ‘stomach flu’
...
2
...
4
...
6
...
8
...
They are discussed below:
Hepatitis A virus
Characteristics:
1
...
3
...
5
...
Family: Picornaviridae
Heat stable (600 C for 1 hour) and acid stable (pH 1 for 2 hours)
Inactivated in food heating to >850 C for 1 minute and disinfecting surface by sodium hypochlofite (1:100)
It is destroyed by
• Autoclave (1210 C for 20 minute)
• Boiling in water for 5 minutes
• Dry heat (hot air oven)
• 1800 C for 1 hour
• UVL (1 minute at 1
...
49
Transmission and epidemiology:
1
...
3
...
5
...
Incubation period: 15 to 50 days
...
Children are the most frequently infected group and outbreaks occur in special living situations such as summer
camps and boiling schools
...
Pathogenesis: The pathogenesis of HAV infection is not completely understood
...
↓
Replicates in the GIT
...
↓
Infects hepatocytes of liver
...
↓
The infection is cleared, the damage is repaired and no chronic infection ensues
...
1 to 3 weeks later IgG antibody is produced, which provides lifelong
protection
...
2
...
4
...
6
...
Fever, anorexia, nausea, vomiting and jaundice are typical
...
Most cases resolve spontaneously in 2 to 4 weeks
...
No chronic hepatitis or chronic carrier state occurs, and there is no predisposition to hepatocellular carcinoma
...
It detects current infection
...
A four-fold rise in anti HAV IgG antibody titer detects current infection
...
Prevention of hepatitis A virus infection:
A
...
Notification
...
Complete bed rest
...
Disinfection of feces and fomites
...
Control of transmission:
1
...
2
...
3
...
4
...
C
...
• Passive immunization: Human immunoglobulin is indicated to induce passive immunity in-
50
1
...
3
...
Close personal contacts of patients with HAV
...
Doses- 0
...
Hepatitis E virus
Characteristics:
1
...
3
...
It is an RNA virus
...
Animal strains of HEV are common throughout the world and is found in rodents, pigs,
sheep and cattle
...
Mode of transmission: Fecal – oral by taking contaminated foods and drinks
...
Hepatitis E is a major concern in developing countries
...
Mechanism: HEV usually causes an acute, self-limiting disease similar to HAV
...
The virus is transmitted by fecal oral route
...
↓
Portal circulation
...
↓
Cytotoxic T cells attack virus infected hepatocytes and cause the damage to the hepatocytes
...
Clinical manifestations: HEV infections manifest with similar symptoms to other forms of acute viral hepatitis and
range in severity
...
Control of reservoir: It is done by1
...
2
...
3
...
B
...
Hand washing after toilet
...
Hand washing before eating
...
Sanitary disposal of excreta
...
Purification of community water supply
...
2
...
It is an RNA virus
...
Genera: Enterovirus
51
4
...
1 ppm Cl, but higher degree of heat or higher
concentration of Cl is needed when present in food
...
Transmission: By eating contaminated milk, beverages, prepared food and water
...
2
...
By vaccination
By taking pasteurized milk
Avoiding contamination of water or drinks or foods
...
2
...
They are round viruses with a ragged outline
...
The genome does not contain any virion polymerase
...
It is spread by contact with infected person, taking contaminated
food or water or by touching contaminated surfaces
...
Disease: Gastroenteritis in adults
...
Aerosolised vomitus
has also been implicated as a transmission mode
...
It is
accompanied by low-grade fever, abdominal cramps and myalgia
...
Norovirus
gastroenteritis is short-lived and typically lasts for 24 – 48 hours
...
↓
Replicates in the cytoplasm with release of viral particles on cell destruction
↓
Intestinal epithelium appears to remain intact
...
↓
Intestinal inflammation
↓
Gastroenteritis
↓
During acute infection, there is transient malabsorption of D-xylose, fat and lactose, which could be related to
shortened microvilli and decreased brush border enzyme activity
...
2
...
4
...
The best way to prevent norovirus is to practice hand washing and general cleanliness
...
By cooking oysters and other shellfish thoroughly before eating them
...
By cleaning and disinfecting contaminated surfaces
...
2
...
4
...
Family: Reoviridae
There are five species (A – E) plus two tentative species (F and G)
...
But adults
and older children can also become infected with rotavirus
...
Disease: Rotavirus diarrhea
Symptoms: Once a person has been exposed to rotavirus, it takes about 2 days for symptoms to appear
...
Vomiting and watery diarrhea may last from 3 to 8 days
...
A common complication is dehydration caused
by a loss of bloody fluids, with resulting electrolyte imbalance
...
Vaccinated and unvaccinated children may develop rotavirus disease more than once because there are many different
types of rotaviruses and because neither vaccine nor natural infection provides full immunity from future infections
...
Transmission: Rotavirus is highly contagious and can be spread by contaminated hands, objects (toys, surfaces), food
and water
...
Thus exposing food and unaffected
persons to the virus
...
It does not cause infection in mucosa of the stomach and large intestine
...
↓
Non-structural protein 4 (NSP4) of the rotavirus may act as a viral enterotoxin, which causes secretion of fluids
by stimulating a signal transduction pathway
...
↓
The resulting diarrhea is due to impaired sodium and glucose absorption, as damaged cells on the villi are
replaced by non-absorbing immature crypt cells
...
↓
53
The damaged cells are released into the lumen of intestine, releasing large quantities of viruses in the diarrheic
stool
...
Hence, the rotavirus produces watery
diarrhea similar to that seen in cholera
...
2
...
Rotavirus vaccine are very effective in preventing rotavirus gastroenteritis
...
• RotaTeq® (RV5), which is given in 3 doses at ages 2 months, 4 months and 6 months
...
• Both rotavirus vaccines are given orally, but they differ in the number of doses given
...
Adenovirus
Adenovirus causes vomiting and diarrhea sometimes accompanied by respiratory tract syndromes (coughing) in young
children
...
Astrovirus
Astrovirus causes gastrointestinal symptoms
...
In children under 4 years, symptoms usually appear within 1 to 3 days of infection
...
Symptoms are the same as for Rotavirus; vomiting for up to 48 hours which is generally
followed by 24 hours of diarrhea
...
54
4
...
Not all of these procedures are readily adaptable to all foods, however
...
A
...
All microbial cells are counted
...
Direct microscopic count and
b
...
Direct microscopic count (DMC): With this method, the results are obtained sooner than with most
other procedures because no incubation period is needed for the cells to metabolize and multiply
...
↓
A counting chamber is used usually, but for food, most often a portion (0
...
↓
For products, such as eggs or cream, xylene or another suitable solvent is added prior to
staining to remove the fat from the material
...
↓
Several stains are done
...
The
number of fields to be examined and counted is inverse to the number of cells and clumps
observed in each field
...
The diameter (d) is measured with a stage micrometer to the nearest 0
...
Since the field is a circle, the area can be calculated: A = πr2
↓
The average number of cells or clumps per field is calculated and divided by the area of the
field to obtain the number per mm2
...
The resultant
number is then multiplied by the dilution factor which, in the case of liquid food (milk) is 100
(0
...
01 ml of a 1:10 dilution)
...
The DMC is a rapid method because an estimate of the bacterial load can be obtained in a
short time
...
Little work is required
...
The test is not too difficult
...
Very little apparatus or equipment is needed except for a microscope
...
The prepared slide can be stored and maintained as a permanent record
...
Some idea as to the type of organism (cocci or rods) is obtained
...
Counts represent organisms in the original product (if it has been treated, such as heat)
...
Preservatives can be added to the sample for holding prior to analysis, for shipment or to
hold for further study, so that organisms do not multiply
...
Only a small amount of sample is needed, which is of value if the product is expensive
...
Electronic particle count: The electronic counter is based on the principle that cells are poor electrical
conductors as compared to an electrolyte solution
...
↓
Each cell passing through the aperture displaces an equal volume of the electrolyte solution
and causes a momentary increased impedance to the flow of electric current
...
These pulses are amplified and counted
...
↓
Since background particles, such as those that occur in foods, also would produce pulses as
they pass the aperture, or could clog the aperture, the particles must be removed
...
Viable counts: Several methods exist to estimate the number of viable microorganisms in foods
...
a
...
The procedure is relatively simple
...
The type of agar used for
the SPC is non-inhibitory and nutritious, unless specific microbial types are to be determined
...
↓
56
The medium and inoculum should be mixed thoroughly to distribute the cells uniformly
...
↓
The temperature and time of incubation will vary depending upon the type of cells that are
being determined (psychrotrophs, mesophiles or thermophiles)
...
↓
During the incubation period, growth and multiplication of cells will occur until a visible
colony is formed
...
↓
The number of colonies are multiplied by the dilution factor and reported as the number of
colony-forming units (CFU) per gram of food
...
Plate count (surface):
In this system, the sterile melted and cooled agar is poured in sterile petri plates
...
The incubation dries the surface of
the agar so that when plated, the organisms do not coalesce
...
↓
Aliquots of dilutions are added to the dry surface and uniformly spread over the agar by
means of a sterile glass rod, bent into the shape of a hockey stick
...
↓
In the plate loop system, a calibrated loop is fitted into the barrel of a repeating syringe
...
↓
With the drop plate method, 0
...
5 to 2
...
Six to eight drops are placed on an agar
surface in a petri plate, with no further manual spreading
...
↓
Automated devices e
...
spiral palter for distributing the samples over the agar surface can also
be used
...
By
varying the amount of inoculum, the equivalent of three dilutions can be plated on one agar
surface
...
Also, the colonies can be counted manually with
the use of a spiral grid system
...
Roll tube: The basic idea of the role tube is the same as for the pour plate method, except that screwcapped test tubes or bottles are used in place of petri plates
...
↓
When the melted agar is cooled to 420 C to 450 C, 0
...
↓
The roll tubes are inoculated upside down so that any water that condenses collects below
the inoculated agar and does not smear the colonies
...
↓
Multiplying the colony count by the dilution factor yields the number of microorganisms per
gram of food
...
Burri strip or slant: The Burri slant method is a simple test for the evaluation of plant sanitation
...
Test tubes can be used, but the oval tube gives a larger surface for the growth of colonies
...
↓
After incubation at 32 – 370 C for 24 hours in a horizontal position, the surface is examined
for microbial growth
...
e
...
This system is a more rapid method than
the plate count, since only 3 to 8 hours of incubation are used
...
The little plate, slide plate and
microplate methods give results comparable those for the plate count
...
1 ml of milk is mixed with about 2 ml of nutrient agar
...
↓
After incubation for 3 to 8 hours in a moist chamber, the slides were air-dried, flame-fixed
and stained for counting
...
f
...
Prefiltering is done to remove food particles that might clog the membrane filters
...
↓
The retained microorganisms are cultured by aseptically transferring the filter onto a nutrient
agar or one that is selective, differential or both
...
↓
58
After incubation for 24 to 48 hours, the colonies can be counted similarly to the APC
...
1% toluidine blue
...
Reportedly, this reading is related to the number of
cells on the filter
...
Tube dilution: The tube dilution method is essentially the aseptic inoculation of a series of tubes of
sterile nutrient broth with a series of dilutions of the food
...
↓
If no turbidity is evident, it is assumed that no microorganisms were present or were able to
multiply
...
↓
If the tube with the 1:100 dilution showed growth and the tube with 1:1000 had no growth,
there were between 100 and 1,000 organisms in the food
...
It gives only an estimate of the range of bacteria that are present
...
Most probable number (MPN): MPN analysis is a statistical method
...
The method is based on the fact that the greater the number of bacteria, the more dilution is needed
to reduce the density to the point at which no bacteria are left to grow in the tubes in a dilution series
...
The pattern of (+) and (–) scores
are then interpreted with appropriate statistical table to obtain the MPN of microorganisms per
volume of sample
...
Presumptive test
2
...
Completed test
They are discussed below:
1
...
3
...
If the presumptive test is negative, no further testing is performed and the
water source is considered microbiologically safe
...
Confirmed test: Some microorganisms other than coliforms also produce acid and gas from
lactose fermentation
...
Completed test: Since some of the positive results from the confirmatory test may be false, it is
desirable to do completed tests
...
Types of analysis
Total coliforms (incubated at
350C)
Fecal coliforms (incubated at
44
...
20C
Fecal streptococci (incubated
at 350C)
Medium
Lactose
or
lauryl
tryptose broth
EC medium
Positive reaction
Gas and/or acid
Azide dextrose broth
Growth
Gas and/or acid
Advantages:
1
...
2
...
3
...
4
...
It is an effective method of analyzing several samples such as sediments, sludge, mud, etc
...
It takes a long time to get the results
2
...
Requires more hardware (glassware) and media
4
...
The metabolic products that are produced can be determined and
used to estimate microbial populations or the quality of the food
...
This involves an oxidation-reduction reaction; the energy substance becomes oxidized, while
another compound is reduced
...
When a compound loses an electron, it becomes oxidized, and another compound which
accepts this electron is reduced
...
Since these reactions consist of electron transfers, they can be measured electrically with a
potentiometer and are expressed by the electrical unit, the volt
...
Besides being determined potentiometrically, the redox potential can be determined with indicators or dyes
...
If such a compound is added to a
substrate containing metabolizing bacteria, electrons may be transferred to the indicator, and its color will be
altered
...
The reduction time is inversely proportional
to the number of cells present
...
The reductase tests usually are
called dye reduction tests, apparently because the dye methylene blue is used
...
During reduction, methylene blue becomes colorless
...
Also, it has been suggested as a means to predict the sterility of
heated food and to estimate the number of bacteria in ground beef
...
The blue color goes through various shades of
purple and mauve to pink
...
This color change to pink is not reversibly by atmospheric O2
...
The resazurin test is a simple, relatively
rapid, inexpensive system to determine the quality of fresh scallop meat and frozen shrimps
...
The TTC is colorless in the oxidized state but forms
intensely colored pink to red pigments (formazans) when reduced
...
This indicator can be used to distinguish bacterial
colonies from food particles in an SPC
...
The food industry relies on these organoleptic testes to determine certain quality attributes of
foods
...
Chemical indicators can be used to evaluate the quality of food in a more objective manner
...
These changes may be desirable or
undesirable, depending upon the food, the microorganisms that are present, and the end products of the
reaction
...
61
The main reactions occurring in foods are catalyzed by enzymes
...
Some chemical reactions, such as oxidation, occur in foods without
specific enzymes to catalyze them
...
The type and amount of metabolic products formed depends upon the kind of food, (protein, carbohydrate or
fat), the type of microorganisms (proteolytic, saccharolytic or lipolytic), the availability of O 2 (aerobicoxidation, decay, or oxidative rancidity; anaerobic fermentation, putrefaction, or hydrolytic rancidity), the
temperature (psychrotrophic, mesophilic or thermophilic organisms) and the types of inhibitors that might be
present
...
As the pH is varied,
the water binding capacity of protein changes
...
The fluorescence of liquid egg is related to mustiness and growth of certain bacteria, while pyoverdine, a
fluorescent pigment produced by pseudomonads, has been determined in frozen whole egg and on poultry
carcasses
...
If carbohydrates are present and fermented, the pH will tend to decline
...
0 with 0
...
If
more than 2
...
Extract release volume (ERV): A meat deteriorates, there is an increase in the amount of water
retained and a degree in ERV
...
Regardless of the microbial quality of the meat, the maximum ERV occurred at pH 5
...
Adenosine triphosphate (ATP): During metabolism, cells form high energy phosphate bonds stored in ATP
...
When an animal dies and the muscle glycogen is utilized by anaerobic glycolysis, the amount of ATP
decreases
...
In starved cells, the
ATP falls to low levels before the loss of viability is evident
...
The method for determining ATP is based on the firefly reaction
...
Crude
extracts from the firefly, when reacted with adenosine diphosphate (ADP), have caused light emission
...
For the assay, it is necessary to eliminate the non-bacterial ATP and then to release the bacterial ATP to react
with the luciferin-luciferase system
...
Another method is the centrifuging and/or filtration of a food to separate the bacterial cells from food
cells
...
The ATP system is relatively simple and rapid
...
Measurement of gas production: When organisms metabolize compounds, CO2 is produced as a metabolic
product and O2 is consumed
...
The detection time of 14CO2 is proportional to the logarithm of
the original inoculum
...
LAL assay: Limulus Amoebocyte Lysate (LAL) forms a gel in the presence of small amounts of
endotoxin from Gram-negative bacteria
...
[Basic Food Microbiology, 2nd edition
By George J
...
2
...
4
...
To determine how the food stuffs become contaminated
...
To determine how such growth could take place
...
Publicity regarding the outbreak, educating people regarding its causes, transmission and prevention
...
2
...
For an investigation, at times, cooperation is needed between epidemiologist, health officer,
physicians, nurses, veterinarians, sanitarians, sanitary engineers, laboratory technicians and statisticians
...
• Collects specimen from suspected foods, from patients or food handlers and send them to laboratory
...
• Prepares appropriate reports and made them available to team leader and laboratory group
...
Laboratory group: Laboratory group performs microbiological and chemical tests as needed, records the
findings and send them to team leader
...
2
...
4
...
6
...
8
...
10
...
Sterile containers
Sampling devices for sampling
A thermometer
A spirit lamp
Sterile swabs in diluent
Sterile wrapping paper
Tape for sealing the samples
Sterile paper towels
Ice
An insulated chest for conveying samples
Forms for recording data
The laboratory should be informed beforehand so that they can be prepared for performing necessary microbiological
and chemical tests on receipt of samples
...
The filed investigation:
Criteria:
1
...
3
...
Prompt reporting of an outbreak to the health department is most important to make the investigation
successful
...
Prompt initiation of investigation is also important because samples may be available for short time
...
Gathering information: A complete inspection is made immediately of the place where foods were prepared
and consumed and the results are recorded on appropriate forms
...
5
...
The time of taking particular food, whether become or not
...
All the data should be summarized in a second form and by means of these suspected food should be located
...
2
...
4
...
Samples of all leftover foods should be collected aseptically
...
All samples should be taken in closed, sterile container and should be sealed with date and time of sealing with
name of person who collected and sealed the sample
...
In case of possibility of legal actions, the samples should be collected, labeled and sealed in presence of witness
...
2
...
4
...
Specimens may be obtained from patients with food illness or from handlers, sometimes for the purpose of
finding the causative organism of the outbreak and to ascertain the ultimate source of the pathogen
...
Cultures from the nose, throat and skin lesions of food handlers are made to test for Staphylococcus able to
produce enterotoxin
...
Tests might be done to find out carriers among
food handlers or to identify the cause of illness in patient
...
g
...
Vomits may be tested when chemical poisoning is suspected
...
The more complete the information is, the better the laboratory can select the type of examination to be used
...
Firstly, microscopic or Gram stained
smear of liquid or from sediment of homogenized, centrifuged food is done
...
Other tests are according to necessary
...
The results of field and laboratory investigations, if complete, can lead to incrimination of the guilty food and
location of the ultimate source of the cause of food borne disease outbreak
...
When an outbreak is small as within a family, the location of the food responsible may be fairly simple
...
When the number of involved persons in an outbreak is fairly large, it is difficult to obtain complete and
accurate data
...
An aid to finding to offending food is a comparison of percentage of persons who ate each food without
becoming ill with the presence of those who become ill
...
5
...
6
...
7
...
8
...
9
...
10
...
11
...
12
...
Preventive measures: The general principles of prevention of food borne outbreaks are:
1
...
65
2
...
4
...
To eliminate opportunities for growth of pathogens, toxigenic or infective agents in foods: This is done
by adjustment of composition, prompt consumption after preparation of perishable foods if they must be held
for any considerable time
...
To reject suspected food
To educate the public better concerning the causes and prevention of food borne illnesses and dangers
involved
Title: Blueprint Food Microbiology
Description: This document contains elaborate study materials of Food Microbiology course for both Bachelor's and Masters level. All the topics covered those taught at various prestigious institutions all over the world. It covers all the books listed in the “Booklist” section. The most easy-to-understand topics are selected from various textbooks and screenshots from those books are added as well. Total page: 66.
Description: This document contains elaborate study materials of Food Microbiology course for both Bachelor's and Masters level. All the topics covered those taught at various prestigious institutions all over the world. It covers all the books listed in the “Booklist” section. The most easy-to-understand topics are selected from various textbooks and screenshots from those books are added as well. Total page: 66.