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Microbial Growth
Requirements for Microbial Growth
• Physical/Environmental requirements

• Chemical buffer – peptones and amino
acids, phosphate salts (non-toxic chemical
that can be add as buffers, also provide essential
growths for bacteria)
-role of chemical buffer is maintaining the pH level
-add chemical buffers to maintain the neutral ph

• pH
• Temperature
• Osmotic pressure
• Chemical requirements
• Oxygen
• Carbon

1
...
0)
- Tomato Juice Agar
2
...
5 – 7
...
Psycrophiles – cold-loving microbes
-optimum growth: 15 o C

2
...
Thermophiles – heat-loving microbes

-too much salt in preparing the food can prevent the
growth of bacteria by destroying the cell of bacteria

Minimum Growth Temperature – lowest temperature
a species can grow

- cannot spoil because it causes plasmolysis to
bacteria

- bacteria can grow in a minimum temperature
Optimum Growth Temperature -temperature in
which a species grow best
-bacteria can also grow best in Optimum Growth
Temperature
Maximum Growth Temperature – highest
temperature at which growth is possible for a
species to grow
-after reaching the Maximum growth temperature,
the rate of growth drops

Food Spoilage Temperature
(refrigeration)
decreases
the
microbial
reproduction rate and not prevent spoilage or not to
kill the microbe

• Require water for growth and are
made up of 80-90% water
• Addition of salts to a solution, to
preserve food
• Extreme halophiles –microbes that are
highly adaptable to high salt concentration, in order
for the to grow
- they are obligate halophiles – need salt for them to
grow

– ex
...
Carbon – function as structural organic molecule,
use as synthesis of cellular components, energy
source
- need by all organic compound that made up the
living cell

a
...
Chemoautotrophs and photoautotrophs – use
carbon from CO2

c
...
Nitrogen – for the synthesis of Protein, RNA,
DNA, ATP
- from ammonium ion or the nitrates
- photosynthesizing cyano-bacteria - uses gaseous
nitrogen from the atmosphere (Nitrogen Fixation)

• Most bacteria decompose proteins
• Some bacteria use NH4+ or NO3
• A few bacteria use N2 in nitrogen
fixation

3
...
Staph, Strep, Enterobacteriaceae



• Inorganic elements required in small
amounts
-function as enzyme cofactor

Facultative Anaerobes

-microorganisms that grow either in aerobic or
anaerobic conditions however greater growth with
the absence of oxygen

Aerotolerant Anaerobes

--microorganisms that can grow in anaerobic
condition however in presence of oxygen they can
still grow

Ex
...
Sulfur
• Synthesize amino acids and vitamins (thiamine,
biotin)

• Important natural sources of sulfur include the
SO4 2- or H2S or AA



Microaerophilic organism

- they are also anaerobic but have a strict
requirement on the presence of oxygen
- can grow only into 2-8 % of oxygen

Ex
...
Phosphorus
• DNA, RNA, ATP, and membranes
• PO43- is a source of phosphorus
-use to synthesize nucleic acids (DNA, RNA,
Protein, ATP)
-main source is from phosphate ion
- test tube is made up of solid agar
1
...
Oxygen


Obligate/Strict Aerobes

-microorganisms that grow only in the presence of
oxygen

Ex
...
aeroginusa,
Bordetella, Franciscella


Neisseria,

Brucella,

Obligate/Strict Anaerobes

2
...
The colonies are found on the bottom of the test
tube, they don’t need air
4
...
Conies are on the middle of the solid agar

Ex
...
Carbon Dioxide
• Capnophilic – increase growth with carbon
dioxide

• Ex
...
Lag phase – period of adjustment for bacteria
-none or little bacterial multiplication
-simplest form

-can last I hour up to several days

-(1) the cell/prokaryotes itself will expand and
elongate, (2) it will divide or separate into equal
parts, (3) each cells will contain the same number of
chromosomes or DNA

-microbes undergoes intense metabolic activity
Example:
Synthesizing
Replication, etc
...
Log phase – also known as Exponential Phase

-cell form small initial outgrowth called bud

– maximum multiplication in growth of bacteria’s

-the bud enlarges and approach the parent cell
size

-metabolically active

-after reaching the parent cell size it separates
to parent cell/bud out

-most susceptible phase of antibiotics since it will
interfere the growth process of microbes

Example: yeast

3
...
Death phase – decline/degradation process
- more microbial death than number of new cells

Culture Media
-use in the laboratory to grow a microorganism
specifically the bacteria

• Culture medium – nutrient material prepared for

-after heating the agar, transfer it to the culture
media immediately
- 50 OC does not injure the bacteria
-in test tube: slant (held in an angle until agar will
solidify; makes a larger surfaces area for growth of
bacteria’s, deep ( solidify vertically)

the growth microorganism in the laboratory

• Inoculum – introduction of microbes into the
culture medium to initiate the growth

Chemically Defined Media

• Culture – microbes grow and multiply in the culture

- culture media with an exact chemical composition

medium

• Provide energy sources, as well as sources of
carbon, nitrogen, sulfur, phosphorus, and any
organic growth factors the organism is unable to
synthesize
...


Example: Chemohetrotrophs E
...
– incubator (37 oC)

Culture Medium
Agar
• Liquefies at 100 degrees celsius, solidify at 50
degrees celsius
• Usually contained in test tubes or petri dishes
-most common
-solidifying agent
-remain solid in longer period of time
-made from marine alga
-complex polysaccharides
-thickeners for foods such as jellies and ice cream

-use for autotrophic, heterotrophic and fungi

• Made up of nutrients such as yeasts (b vit
...
6)
- use to isolate fungi that grows most bacteria at this
pH 5
...
5 % sodium chloride – role is it
discourages the growth of competing bacteria and
select favor

-fourth streak/ the last streak – pure culture or
sample give distinct or visible colonies, can see an
individual colony

• MacConkey agar (bile salts and crystal violet)
– distinguish between lactose fermenters and
no fermenters (violet)

-Easier to watch in a microscope

- red and pink colonies
-non lactose fermenters are the colorless/yellow
colonies
-usually gram negative bacteria while the nonlactose are the gram positive bacteria
-use to distinguish the different salmonella species

-streaking to see visible colonies

Preserving Bacterial Cultures
• Deep-freezing
- Process in which a pure culture of microbes is
placed in a suspending liquid and quick frozen
at temperatures ranging from -50 to -95 degrees
celsius
...


-it can culture even after deep freezing up to several
years

• Lyophilization (freeze-drying)

- usually made into liquid and put in a testube
-use to detect water sample

- Suspension of microbes is quickly frozen at
temperatures ranging from -54 to -72 degrees
celsius and water is removed by a high vacuum
- the product here is a dry powder/substance; it
removes moisture on the substance

- need to hydrate in order the culture to be alive
again

(incubate to allow the growth of bacteria in both
methods)

-hydrate to a suitable liquid nutrient medium

-after promoting the growth of bacteria, we count na
the colonies hahaha

Direct Measurements of Microbial
Growth
1
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Plate Count

- transfer 1 ml of inoculum in the sample to another
sample in the test tube(dilute to several test tube) ; it
allows the growth or to be visible the amount of
microorganism on the test tube
-purpose is to ensure that some colonies counts will
be within the range

-simply count the visible colony that are seen
-colony counter – count colony per squre

2
...
Inoculate Petri plates from serial dilutions

- end inoculum can be transferred to petri dish, there
are 2 methods:

- use for water samples

1
...
Spread plate Method

-useful for growth of bacteria in a liquid differential
medium to identify the microbes (Ex
...
5 ml; 1 test tube is positive

1
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Direct Microscopic Count

- if little can pass through the light to the bacterial
suspension therefore less light can reach the
detector
-more turbid the solution - higher absorbance value
-10- 100 million cells per ml need to make the
suspension turbid, enough to read in the
spectrophotometry

2
...
Dry weight – use in filamentous bacteria and
molds
- remove the bacteria in a culture, let it dry and after
weigh it
-by weighing you can determine the number of
bacteria



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