microbiology

1. ASSIGNMENT PRESENTATION OF
MICROBIOLOGY
TOPIC- STERILIZATION
BY
CHEMICAL MEANS

2. STERILIZATION BY CHEMICAL MEANS
• Chemical agents are used on living tissues (as
antiseptics) and on inanimate objects (as
disinfectants).
• Few chemical agents achieve sterility.
• Careful attention should be paid to the properties and
concentration of the disinfectant to be used.
• The presence of organic matter, degree of contact
with microorganism and temperature should also be
considered.

3. DISINFECTION
• Disinfection is a process which is effective principally on non-acid fast vegetative
organism. Disinfectants are chemical agents that may kill vegetative bacteria ,fungi
and viruses and occasionally , spores by the destruction of proteins,lipid or nucleic
acids in the cell or its cytoplasmic membrane.
The European committee for the standardisation of Disinfectants define disinfection
as the “selective elimination of certain undesirable organism in order to
prevent their transmission, achieved by action on their structure or
metabolism , irrespective of their functional state”.
Disinfectants are used in clinical practice to decontaminate surfaces that have been
in contact with body fluids, tissues or mucosa, pathalogical specimens or
microbiological cultures. They may be used for medical devices where sterility is
not required, i.e. when there is no risk of implanting spores into sterile tissues. They
are also used when items or surface are too large to be processed in a disinfector or
are heat labile, or otherwise too fragile to withstand the washing process.

4. Properties of an ideal disinfectant
• An ideal disinfectant should:
• Be fast acting even in the presence of organic substances, such as those in body
fluid; (resistant to inactivation)
• Be effective against all types of infectious agents without destroying tissues or
acting as a poison if ingested; (broadly active)
• Easily penetrate material to be disinfected without damaging or discoloring the
material; (not poisonous or otherwise harmful)
• Be easy to prepare & stable even when exposed to light, heat or other
environmental factors; (penetrating; not damaging to non-living materials)
• Be inexpensive & easy to obtain & use.(stable; easily prepared)
• Not have an unpleasant odor.(not unpleasant to work with).

5. Factors influencing the activity of disinfectants
• The concentration of the chemical agent.
• The temperature at which the agent is being used. Generally, the lower the
temperature, the lower the effectiveness.
• The kinds of microorganisms present . Endospore producers such as Bacillus
species, Clostridium species, and acid –fast bacteria like Mycobacterium
tuberculosis, are harder to eliminate.
• The number of microorganisms present. The more microorgsanisms, present , the
harder is to disinfect.
• The nature of the material bearing the microorganisms . Organic materials such as
dirt & excreta interferes with some agents.
• The pH of solution should be optimum..

6. Evaluation of a disinfectant
• Phenol coefficient: This value expresses the capacity of a disinfectant to
kill bacteria when compared with phenol. It is the highest dilution of the
disinfectant divided by the highest dilution of phenol, which will kill the
test organism in 10 min but not in 5 min under standard condition . The
disinfectant is generally recommended for us at five times this
concentration . Species strain of Salmonella Typhi or Staphylococcus
aureus is used as the test organism.
• Use-dilution test: The survival of bacteria (Salmonella choleraesuis,
Staphylococcus aureus, & Pseudomonas aeruginosa) in the manufacturer’s
recommended dilution of a disinfectant is determined.
• Disk-dilution method: A disk of filter paper is soaked with a chemical and
placed on an inoculated agar plate, a clear zone of inhibition indicates
effectivenes.

7. Modes of action
• Protein denaturation
• Membrane disruption
• Nucleic acid damage
• Inhibition of metabolism

8. Types of disinfectants
• Phenol & phenol derivatives: Phenol (5-10%) was the first disinfectant commonly
used. However, because of its toxicity and odor, phenol derivatives are now
generally used. These include orthophenylphenol hexachlorophene , triclosam,
hexylresoreinol, & chlorhexidine. These agents kill more bacteria , most fungi, and
some viruses, but are usually infective againt endospore. They alter membrane
permeability & denature proteins.
• Soaps & detergents: Soaps are only mildly microbicidal. Their use aids in the
mechanical removal of microorganisms by breaking up the only film on the skin
(emulsification) and reducing the surface tension of water so it spreads & penetrates
more readily. Some cosmetic soap contains added antiseptics to increase
antimicrobial activities.
• Alcohols: 70% solution of ethyl or isopropyl alcohol are effective in killing
vegetative bacteria , enveloped viruses, and fungi . However they are usually
infective against endospores & non-enveloped viruses. Once they evaporate, their
cidal activity will cease. Alcohols denature membranes & are often combined with
other disinfectants , such as iodine, mercurials, and cationic detergents for increased
effectiveness.

9. • Acid & alkali: Acids & alkalies alter membrane permeability and denature
proteins & other molecules. Salts of organic acids , such as calcium propionate ,
potassium sorbate & methylparaben ae commonly used as food preservatives.
Undecylenic acid is used for dermatophyte infections of the skin. An example of
an alkali is dye. (sodium hydroxide).
• Heavy metals: Heavy metals, such as mercury ,silver & copper, denature proteins
. Mercury compounds (mercurohrome, metaphor, merthiolate) are nly
bacteriostatic and are not effective against endospores. Silver nitrate (1%) is
sometimes put in the eyes of newborns to prevent gonococcal opthalamia. Copper
sulphate is used to combat fungal diseases of plants & is also a common algicide.
Selinium sulfide kills fungi & their spores.
• Chlorine: Chlorine gas reacts with water to form hypochlorite ions, which in turn
denature microbial enzymes. Chlorine is used in the chlorination of drinking water,
swimming pools , and sewage. Sodium hypochlorite & chloramines ( chlorine plus
ammonia) are used to santize glassware, eating utensils , dairy & food processing
equipment, and hemodialysis system.

10. In some instances the site of action is dependent upon the concentration of the disinfectant.
SITE OF
ACTION
Alcohols chlorine Formald
ehyde
glutaral
dehyde
Metal
salts
Iodine Phenols Quatern
ary
compou
nds
Cell wall +
Cytopls-
mic
membra
ne
+ + +
Proteins
denatur
ation
+ + + +
Nucleic
acids
+
Enzymes + + +

11. • Iodine & iodophores: Iodine also denatures microbial protein & is usually
dissolved in an alcohol solution to produce a tincture. Iodophores are a combination
of iodine & anionic detergent that reduces surface tension & slowly releases the
iodine .Iodophores are less irritating than iodine & do not stain . They are generally
effective against vegetative bacteria, Mycobacterium tuberculosis , fungi some
viruses & some endospores.
• Aldehydes: Aldehydes , such as formaldehyde and glutaraldehyde, denature
microbial proteins. Formalin (37% aqueous solution of formaldehyde gas) is
extremely active & kills most forms of microbial life. It is used in embalming,
preserving biological specimens , and in preparing vaccines . A 10 hour exposure to
a 2% glutaraldehyde solution can be used for cold sterilization of materials.
• Oxidizing agents : This group include hydrogen peroxide & potassium
permanganate, which are antiseptic. These are less stable. These act by causing per
oxidation of cell membraane.
• Biguanides compounds : Chlorhexidine damages plasma membranes of vegetative
cells. It is bactericidal in high dilution, but viruses ,spores & mycobacteria are
relatively resistant.

12. CHEMICAL AGENT RECOMMENDED USE LIMITATIONS
Phenol & phenolics General disinfectant Microbial effectiveness
limited ,I rritating,corrosive
Alcohols-ethyl & isopropyl Skin & thermometer
antiseptic
Antiseptic
Iodine Disinfect skin Irritating to mucous
membrane
Chlorine Water disinfection Inactivated by organic
material ;pH dependent for
effectiveness;
objectionable taste &
odour
Silver nitrate Treating burns Possible irritation
Mercurial Skin disinfection Slow-acting toxic
Ammonium compounds Skin disinfection Non-sporicidal
Formaldehyde Fumigation Poor permeation
Glutaraldehyde Fumigation Limited stability

13. Gaseous chemosterlizers
• Chemical sterilization is a popular method for sterilizing heat sensitive solid
objects . This method kills by exposing organism to a toxic chemical . Ethylene
oxide , ethanol, mercuric chloride, hypochlorites are the common chemical agents
used for sterilization.
• Ethylene oxide: It is the gas most frequently used for sterilization . It penetrates
most materials and kills all microorganism by protein denaturation (alkylates
proteins and block the amino groups). It is used to sterilize wrapped disposable
plastic ware. Exposure to this gas is for 5-8 hours at 38 degree celsius or 3-4 hours
at 54 degree celsius . Since it is explosive , it is usually mixed with inert gases such
as freon or carbon dioxide.

14. CHEMICAL FOOD PRESERVATIVES
• SO2, sorbic acid, benzoic acid & propinoic acid inhibit fungal metabolism and are
used as food preservatives.
• Nitrate and nitrite salts prevent germination of Clostridium endospores in meats.
• ANTIBIOTICS
Nisin and natamycin are antibiotics used to preserve foods, especially cheese.