1. Sterilization and Disinfection
Presented by
R.Parthasarathy

2. TERMS AND DEFINITIONS
Sterilization
The process by which an article, surface or medium is freed of all
viable microorganisms either in the vegetative or spore state is known as
sterilization.
Disinfection
• The process of destruction of pathogenic microorganisms by direct
exposure to chemical and physical agents are called as disinfection.
• The agents used to achieve these state is called disinfectant.
• Chemical disinfectants which can be safely applied to skin or mucous
membrane and are used to prevent infection by inhibiting the growth of
bacteria are called antiseptics.
Bactericidal agents and germicides
Agents which are able to kill bacteria.
Bacteriostatic agents
Agents which prevents the multiplication of bacteria ( doesn’t kill).

3. Various Agents In Sterilization
PHYSICAL AGENTS CHEMICAL AGENTS
Alcohols:
Sunlight
Ethanol, isopropyl
Aldehydes:
Drying
Formaldehyde, Glutaraldehyde
Dry heat :
Dyes
Hot air oven, Incineration, Flaming
Moist heat:
Boiling, Pasteurization, tyndallisation, Auto Halogens
claving
Filtration Phenolic compounds
Gases
Radiation
Ethylene oxide, Formaldehyde, beta
Ionizing, Non Ionizing
propiolactone(BPL).
Ultrasonic vibration Metallic salts and surface active agents

4. Physical Agents:
Sunlight
•Direct sunlight is a natural method of sterilization of water in tanks, rivers and
lakes.
•Direct sunlight has an active germicidal effect due to the combined effect of
ultraviolet and heat rays.
Drying
•4/5 of the bacterial weight is due to water.
•Therefore drying in air has deleterious effect on many bacteria.
•This is unreliable method, spores are unaffected by drying.
Dry heat
Flaming:
Inoculating loop or wire, the tip of forceps are held in a Bunsen flame till they
become red hot.
Incineration:
This medthod is used to destroy contaminated cloth, animal carcasses and
pathological materials.

5. Physical Agents: cont..
Hot air oven
This method is applicable to metals, glassware, and some heat-
resistant oils and waxes that are immiscible in water.
Conditions
171ºc for at least one hour.
160ºc for at least two hour.
121ºc for at least sixteen hour.
Moist Heat:
Method Uses Comments
Water < 100°c (Pasteurization) For sterilization of serum, vaccines 62°c for 15 min.
and body fluids. 72°c for 30 sec.
Spores are not destroyed.
Water at 100°c For sterilization of glassware's, metal Some spores are not destroyed.
and rubber items.
Arnold steamer: For sterilization of culture media Preserves properties of media.
Stream at atmospheric pressure containing gelatin and sugar.
Autoclave : For sterilization of culture media and 121°c at 15 psi for 15-20 minutes.
Stream below atm pressure laboratory materials. Almost Kills all the bacteria and spores.
Flash autoclaves use 134°C for 3 minutes.

6. Physical Agents: cont..
Filteration:
Filtration helps to remove bacteria from large volumes of
fluid, especially fluid containing heat-labile components such as
sera, solution of sugars and antibiotics.
A pore size of 0.2 m is effective because filters act not only
mechanically but by electrostatic adsorption of particles to their
surface.
The filters are of two types (deep and membrane)

7. Physical Agents: cont..
FILTERS
DEEP FILTERS
Made up of Examples Comments and Uses
Candle filters 1.Diatomaceous earth Berkefeld filters They are available in different porosity.
2.Unglazed porcelain Chamberlain filters Mostly used for the purification of
drinking water and industrial uses.
Asbestos filters Asbestos (magnesium Seitz and Sterimat They have high adsorbing capacity and
silicate) filters tend to alkalinize the filtered fluid.
These are disposable , single use discs
available in different grades.
Asbestos is carcinogenic hence its use
is discouraged.
Sintered glass Fusing finely powdered They are expensive and brittle.
filters glass particles They have low absorptive property.
MEMBRANE Cellulose esters They are routinely used for water
FILTERS Other polymers purification and analysis, sterilization,
sterility testing and solutions of
parenteral use.
Wide range of average pore
diameters(APD) are available but
0.2mm size is widely used.

8. Physical Agents: cont..
RADIATION
Non Ionisizing radiation:
Types Produced by Mode of action Uses Comments
Low energy UV lamps DNA damage Infrared rays: Use of UV light
(Infrared and Sterilization of prepacked is limited by
ultraviolet rays) items such as syringes penetration and
and catheters. hazardous.
Ultraviolet rays:
Used for disinfecting
operation threatres and
laboratories.
Ionisizing radiation:
High energy Cobalt-60 DNA damage For the sterilization of They are
ionizing type based antibiotics, hormones expensive.
(Gamma rays and instruments and other prepacked They are very
high energy disposable items such effective due to
electrons such as as catheters, gloves, high penetrative
X-rays and syringes, infusion sets, power.
cosmic rays) oils, animal feeds, etc.

9. Physical Agents: cont..
Ultrasonic and sonic vibration:
 High frequency sound waves beyond the sensitivity of human ears are
called as ultrasonic waves.
 They have the property to disrupt the cells but the results have been variable.
 Gram negative rods are more sensitive to ultrasonic vibration whereas Gram
positive cocci, spores of fungi and bacteria are resistant to the vibration.
 Ultrasonic devices are used in dental.
 However, most sonic machines are not reliable for routine use.

10. Chemical Agents: cont..
Properties of Ideal antiseptics or disinfectants should
 Effective against all microorganisms and have a wide spectrum of
activity.
Have speedy action.
Be effective in presence of organic matter.
Be effective in varying pH(acidic and alkaline medium).
Be active in presence of organic matter.
Be stable.
Also compatible with other antiseptics and disinfectants.
Have high penetrating power.
Not corrode metals.
Not cause local irritation or sensitization.
Not interfere with healing.
Not be toxic if absorbed into circulation.
Be cheap and safe.

11. Chemical Agents: cont..
Factors influencing antiseptics or disinfectants:
Time of action.
Temperature.
Concentration of the substance.
pH of the medium.
Nature of the organisms.
Presence of foreign material.
Mode of action
Protein coagulation.
Disruption of cell membrane.
Removal of free sulphydryl groups which is essential for the functioning of
the enzymes.
Substrate competition.

12. Chemical Agents: cont..
Alcohols
Ethyl alcohol, isopropyl alcohol, and n-propanol exhibit rapid, broad-
spectrum antimicrobial activity against vegetative bacteria, viruses, and
fungi but are not sporicidal.
Activity is optimal when they are diluted to a concentration of 60–90% with
water.
Protein slows its action whereas 1% mineral acid or alkali enhances the
action.
Aldehydes
•Formaldehyde is bactericidal, sporicidal, and virucidal.
•It is active against the amino group in the protein molecule.
•Formaldehyde gas is used for sterilizing instruments and heat sensitive
catheters and for fumigating wards, sick rooms and laboratories.
•Glutaraldehyde is used for low-temperature disinfection and sterilization of
endoscopes and surgical equipment.
•It is normally used as a 2% solution to achieve sporicidal activity.

13. Chemical Agents: cont..
Dyes
Two groups of dyes are there
1.Aniline dyes
eg: brilliant green, malachite green, crystal violet
2.Acridine dyes
eg: proflavine, acriflavine, euflavine and aminacrine.
They are used as skin and wound antiseptics.
They are more active against Gram positive organisms than Gram negative organisms.
Halogens
Iodine is an effective disinfectant that acts by iodinating or oxidizing essential
components of the microbial cell.
Iodine is rapidly bactericidal, fungicidal, tuberculocidal, virucidal, and sporicidal.
2% iodine in 50% alcohol (tincture), which kills more rapidly and effectively than alcohol
alone.
Iodophors (eg, povidone-iodine) are complexes of iodine and a solubilizing agent or
carrier, which acts as a reservoir of the active I2.
The most important types of chlorine-releasing agents are sodium hypochlorite,
chlorine dioxide, and sodium dichloroisocyanurate, which are oxidizing agents that
destroy the cellular activity of proteins

14. Chemical Agents: cont..
Phenolic compounds:
The use of phenolic compounds are introduced by the Lister.
The mode of action is due to their capacity to disrupt the cell membrane.
Phenol(carbolic acid) is a potent protein denaturant and bactericidal agent.
It is used as disinfectants for various hospital purposes.
Cresol and Lysol are active against a wide range of organisms but they are
toxic and corrosive.
They are used to disinfect surgical instruments, contaminated materials and
floors.
Halogenated diphenyl compounds such as hexachlorophene and
chlorhexidine.
Hexachlorophene is toxic and should be handled with care.
Cholrhexidene is nontoxic, hence used as skin antiseptic which is more
effective against Gram positive organisms than Gram negative organisms.

15. Chemical Agents: cont..
Gases:
Ethylene oxide is an inflammable and potentially explosive gas.
By mixing with inert gases like CO2 and N2 to concentration of 10% its
explosive tendency is eliminated.
It is an alkylating agent that inactivates microorganisms by replacing labile
hydrogen atoms on hydroxyl, carboxy, or sulfhydryl groups, particularly of
guanine and adenine in DNA.
Under controlled condition it is used to sterilise materials such as glass,
artificial heart valves, respirators, lung machines, equipments and clothing.
Formaldehyde gas and Betapropiolactone(BPL) are used for fumigation of
operation theatres and other rooms.
BPL is more efficient than formaldehyde gas.

16. Chemical Agents: cont..
Surface active agents
These compounds have two regions in their molecular structures, one a
water-repelling (hydrophobic) group and the other a water-attracting
(hydrophilic) group.
They are classified into four groups; anionic, cationic, nonionic and
amphoteric.
They are mainly used as wetting agents, emulsifiers and detergents.
Cationic detergents, particularly the quaternary ammonium compounds
(“QACs") such as benzalkonium chloride, acetyl trimethyl ammonium
bromide are highly bactericidal.
They are effective against Gram +ve organisms than Gram –ve organisms.
They are more active in alkaline pH.
They are inactive against spores and viruses, tubercle bacilli.
Anionnic detergents Eg; common soap.
Amphoteric or ampholytic compounds or tego compounds are active against
Gram+ve organisms than Gram –ve organisms.
Generally it is not used.

17. Chemical Agents: cont..
Metallic salts
Salts of mercury, copper and silver are used as disinfectant.
Mercuric chloride is highly toxic. Hence organic compounds such as
mercurochrome, phenyl mercury nitrate and thiomersal are used as
antiseptics(less toxic).Copper salts are used as fungicides.
Silver salts in aqueous solution have a limited use.
Testing of Disinfectants
Because of numerous parameters which influence disinfectant activity, there
is no reliable test to determine the efficiency of a disinfectant.
However Phenol is used as standard.

18. Thank you