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SCI 305 DISINFECTANTS

Microorganism types
Targets microogorganisms which include:
• Viruses
• Fungi
• Algae
• Bacteria
• Protozoa
• Eggs
• etc
Disinfection prevents diseases such as cholera,
typhoid, diarrhea, hepatitis, amoebiasis

Structure of bacteria

• Fimbriae (sometimes called "attachment pili") are protein
tubes that extend out from the outer membrane in many
members of the Proteobacteria
...
Fimbriae usually function to facilitate
the attachment of a bacterium to a surface (e
...
to form a
biofilm)
• Perhaps the most recognizable extracellular bacterial cell
structures are flagella
...
e
...

• In most bacteria the most numerous intracellular structure
is the ribosome the site of protein synthesis in all living
organisms

Gram positive and gram negative
bacteria
• Danish scientist Hans Christian Gram devised a method to
differentiate two types of bacteria based on the structural
differences in their cell walls
...

• In contrast, Gram-negative bacteria do not retain the violet dye and
are colored red or pink
...

• These bacteria have a wide variety of applications ranging from
medical treatment to industrial use and Swiss cheese production
...
e
...

• Destroys or irreversibly inactivates most
pathogenic microorganisms
• Traditionally include sanitizers, disinfectants,
and sterilants
...


Fractional removal, N/No = Cntm
This is generally simplified to
N/No= Ct
Ct values determined for 99
...
coli

0,009

12

*

Legionella pneumophila

1,05

12

*

Rotavirus

0,006-0,06

5

6-7

Giardia lamblia (cysts)

0,17

25

7
...


Moist Heat
• Moist
heat
denatures
proteins
• Autoclave
: Steam
under
pressure

Figure 7
...
2

Factors in antimicrobial processes
•
•
•
•

Target microorganisms
The media to be treated
The intended use of the media
Presence of interfering materials in the media

Antimicrobial products
• Categories
– 19 % sanitizers
– 80 % disinfectants
– 1% sterilizers

• Selection criteria
–
–
–
–
–

Antimicrobial efficacy
Corrosivity
Chemical hazard
Environmental concerns
Stability

•
•
•

Selection
of
disinfectants
Factors:
The spectrum of organisms to be inactivated
...

The circumstances of use
...
Efficacy against virus will be less if virus is intracellular
...
g
...

pH
...

– Disinfectants containing organic solvents can damage plastic
...
Some may have
toxic or corrosive properties and particular caution must be exercised in choosing powerful
sensitisers such as formaldehyde and glutaraldehyde
...
Consult the manufacturer’s material safety data
sheet
...
Acids
2
...
Aldehydes
4
...
Biguanides
6
...
Oxidizing agents
8
...
Quatenary ammonium compounds

Sites of action of chemical antimicrobial agents
Chemical agents of control have 3 primary sites of action: cell wall & cellular membranes,
proteins and nucleic acids (DNA or RNA)
...

• Acids also change the pH of the environment making it
detrimental to many microorganisms
• Concentrated solutions of acids can be caustic, cause
chemical burns, and can be toxic at high concentrations
in the air
• These characteristics limit their use
• The antimicrobial activity of acids is highly pH dependant
• Acids have a defined but limited use as disinfectants
...

• Acetic acid is typically applied by spraying, misting or
immersing an item in a diluted solution
...
Acetic acid has poor activity in organic
material

Alkalis
• Alkaline agents work by saponifying lipids within the envelopes of
microorganisms
...
Alkalis have good microbicidal properties,
but are very corrosive agents and personal protection precautions
should be observed
• Sodium hydroxide (lye, caustic soda, soda ash) is a strong alkali
used to disinfect buildings but is highly caustic
...
Lye should always be
carefully added to water
...

• Ammonium hydroxide is an effective disinfectant against coccidial
oocysts however strong solutions emit intense and pungent fumes
• This substance is not considered effective against most bacteria
...


Alkalis
• Sodium carbonate (soda ash, washing soda) has been used in a hot
solution (180oF) for disinfecting buildings, which have housed animals
with FMD
• It is more effective as a cleanser than a disinfectant since it lacks efficacy
against some bacteria and most viruses
...

• It can be irritating and requires protective clothing and is harmful to
aquatic life
...

• This has biocidal effects on some bacteria and virus and is sometimes
spread on the ground following depopulation of infected premises and has
also been used to retard putrefaction of buried carcasses after
depopulation
...


•
•
•
•

•

•
•
•
•
•

Alcohols
Include ethanol, isopropanol
Alcohols are broad spectrum antimicrobial agents
denaturing proteins, causing membrane damage and cell lysis
Alcohols are used for surface disinfection, topical antiseptic and hand
sanitizing lotions
...
Ethanol, isopropanol
Denature proteins, dissolve lipids

Table 7
...
Lysol
Bisphenols
...
7

Phenols

Phenols
• Broad spectrum disinfectants
• Function by denaturing proteins and inactivating membrane-bound
enzymes to alter the cell wall permeability of microorganisms
...

• Most commonly used agents are formaldehyde and
gluteraldehyde
– Formalin (37% formaldehyde in water); 2% use level for disinfection
– Glutaldehyde for medical equipment; 2% use levels; Ph dependent

• Effective against bacteria, fungi, viruses, mycobacteria and spores
• Non-corrosive to metals, rubber, plastic and cement
• Highly irritating, toxic to humans or animals with contact or
inhalation, and are potentially carcinogenic
– therefore their use is limited

• Personal protective equipment (i
...
, nitrile gloves, fluid resistant
gowns, eye protection) should be worn when using these
chemicals
...

• Commercial chlorine bleach contains 5
...

• Hypochlorites should never be mixed with
acids or ammonia as this will result in the
release of toxic chlorine

Sodium hypochlorite solutions

Iodine
• Iodine Compounds are broad spectrum and considered effective for a
variety of bacteria, mycobacteria, fungi and viruses
• Function by denaturing proteins to interfere with the enzymatic systems
of microorganisms
• Often formulated with soaps and considered relatively safe
• Concentrated iodine compounds can be irritating to the skin, can stain
clothes or damage rubber and some metals
• Iodine agents are inactivated by QACs and organic debris
• Iodophors are iodine complexes that have increased solubility and
sustained release of iodine
...


Oxidizing Agents
• Oxidizing agents are broad spectrum, peroxide
based compounds that function by denaturing
the proteins and lipids of microorganisms
• Peroxygen compounds vary in their
microbiocidal range, but are considered
effective on hard surfaces and equipment
...

• Its activity against mycobacteria is limited
• Peracetic acid: is a strong oxidizing agent
• a formulation of hydrogen peroxide and acetic
acid
• It is considered bactericidal, fungicidal, sporicidal
and virucidal
• It is also effective against mycobacteria and algae
and has some activity in the presence of organic
material
...


guanides

Quaternary Ammonium Compounds
QUATS/QAC
• Cationic detergents that are attracted to the negatively charged surfaces
of microorganisms, where they irreversibly bind phospholipids in the cell
membrane and denature proteins impairing permeability
• Low level disinfectant
• Highly effective against Gram positive bacteria, and have good efficacy
against Gram-negative bacteria, fungi and enveloped viruses
...
5
...
e
...
gonorrhoeae
Thimerosal (mercury-containing compound) used
to preserve vaccines…problems?
Copper controls algal growth in reservoirs, fish
tanks, swimming pools, and water storage tanks;
interferes with chlorophyll

KIRBY BAUER DISK DIFFUSION METHOD
•
•
•
•
•
•
•
•
•
•
•
•
•

An In-vitro method
Selected standard test strains e
...
E
...

Prepare a solution of 0
...

Prepare Mueller Hinton agar in a plate and first sterilize at 121 oC for 15 minutes
...

Using a sterilized paper punch, make 6mm diameter discs from a Whatman No
...

Impregnate the disks with 10μl of the anti-microbial
Use commercial anti-microbial such as Chloramphenicol and Nystatin as the positive
control and the dluent DMSO as the negative control
Using a sterile forcep, place the discs at equal distance in a circular pattern on the
surface of the Mueller Hinton agar ensuring that each disk is indicated with a label
...

2
...


Metal rings dipped in test bacteria are dried
Dried cultures placed in 500mg/ml disinfectant for
min at 20°C
Rings transferred to culture media to
determine whether bacteria survived
treatment
4
...
00 to 7
...
The
microplates were then incubated at 37oC for 24 hours
under aerobic conditions
...


Evaluating a disinfectant by
Disk-diffusion method

Figure 7
...
Such disinfectants
are capable of steriliza tion when the contact time is relatively long (e
...
,
6 to 10 hours)
...
g
...
These chemical germicides
are potent sporicides and, in the United States, are classified by the FDA
as sterilant/dis infectants
...

• Intermediate-Level Disinfection This procedure kills vegetative
microorganisms, inc luding Mycobacterium tuberculosis , all fungi, and
inactivates most viruses
...
" They are used
commonly in laboratories for disinfection of laboratory benches and as
part of detergent germicides used for housekeeping purposes
...
tuberculosis, some fungi, and inactivates some viruses
...
"



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