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DISINFECTIONby chemicals
basicsDr.T.V.Rao MD
Dr.T.V.Rao MD 1
Why we need Sterilization
• Microorganisms capable of causing infection are constantly present in the external environment and on the human body.
• Microorganisms are responsible for contamination and infection.
• The aim of sterilisation is to remove or destroy them from materials or from surfaces.
Dr.T.V.Rao MD 2
Uses of sterilisation
1. Sterilisation of materials, instruments used in surgical and diagnostic procedures.
2. Sterilisation of Media and reagents used in the microbiology laboratory.
3. Food and drug manufacturing to ensure safety from contaminating organisms.
Dr.T.V.Rao MD 3
How can microorganisms be killed?
1 Denaturation of proteins (e.g. wet heat, ethylene oxide)
2 Oxidation (e.g. dry heat, hydrogen peroxide)3 Filtration4 Interruption of DNA synthesis/repair (e.g.
radiation)5 Interference with protein synthesis (e.g. bleach)6 Disruption of cell membranes (e.g. phenols)
Dr.T.V.Rao MD 4
Factors that influence efficacy of disinfection/sterilization
1 Contact time2 Physico-chemical environment (e.g. pH)3 Presence of organic material4 Temperature5 Type of microorganism6 Number of microorganisms7 Material composition
Dr.T.V.Rao MD 5
Relative Resistance of Microbial Forms
Highest resistance Moderate resistance Least resistance
bacterial endospore (Bacillus & Clostridium)
protozoan cystsome fungal sporessome naked virusvegetative bacteria that have higher resistance ( M. tuberculosis, S.aureus, Pseudomonas)
most bacterial vegetative cellsordinary fungal spores & hypaeenveloped virusYeastsTrophozoites
Dr.T.V.Rao MD 6
Definitions: Sterilisation :
– It is a process by which an article, surface or medium is made free of all microorganisms either in vegetative or spore form.
Disinfection :– Destruction of all pathogens or organisms capable
of producing infections but not necessarily spores.– All organisms may not be killed but the number is
reduced to a level that is no longer harmful to health.
Dr.T.V.Rao MD 7
Antiseptics :
Antiseptics :– Chemical disinfectants which can safely applied to
living tissues and are used to prevent infection by inhibiting the growth of microorganisms.
Asepsis :– Technique by which the occurrence of infection
into an uninfected tissue is prevented.
Dr.T.V.Rao MD 8
Ideal sterilization/disinfection process
• Highly efficacious• Fast• Good penetrability• Compatible with all materials• Non-toxic• Effective despite presence of organic material• Difficult to make significant mistakes in process• Easily monitored
Dr.T.V.Rao MD 9
Figure 9.1 A plot of microbial death rate
Dr.T.V.Rao MD 10
90% die
1 min
90% die
1 min
Constant percentageof the extant populationis killed each minute
Time (min)
Nu
mb
er
of
livin
g m
icro
bes
Chemical Methods
Many matters, substances and objects cannot be sterilized with
Physical methods So Need for Disinfectants
Dr.T.V.Rao MD 11
Chemical methods • Alcohols• Aldehydes• Phenols• Halogens• Oxidizing agents• Salts• Surface active agents• Dyes• Vapour phase disinfectantsDr.T.V.Rao MD 12
Chemical agents • A variety of chemical agents are used as
antiseptics and disinfectants.• Factors influencing the potency of a disinfectant:
• Concentration• Time of action• pH • Temperature• Nature of organism• Presence of organic matter
Dr.T.V.Rao MD 13
Levels of Disinfection1. High level
disinfectants2. Intermediate
level disinfectants
3. low level disinfectants
Dr.T.V.Rao MD 14
High level disinfectants:
• Glutaraldehyde, Hydrogen peroxide, peracitic acid and chlorine compounds.
• Effectiveness may be equal to that of sterilisation.• Used for:
• Endoscopes• Cystoscopies• Surgical instruments with plastic components
Dr.T.V.Rao MD 15
Intermediate level disinfectants
• May not effective against spores
• Includes alcohols, iodophores and phenols
• Used for:– Laryngoscopes– Fiber optic
endoscopes
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Low level disinfectants:
– Many organisms can survive on exposure to these disinfectants.
– Used for items which come in contact with the patients but they do not penetrate into tissues.
– Stethoscopes, ECG electrodes etc.
Dr.T.V.Rao MD 17
Alcohols :
– Ethyl alcohol and Isopropyl alcohol are commonly used.
– Act by denaturing of bacterial proteins.– No sporicidal and virucidal activity.– Used as skin antiseptics.– Isopropyl alcohol is preferred to Ethyl
alcohol as it is better fat solvent, more bactericidal and less volatile.
Dr.T.V.Rao MD 18
Aldehydes:2.
a) Formaldehydeb) Glutaraldehyde
Dr.T.V.Rao MD 19
Formaldehyde: Bactericidal, sporicidal and virucidal Used in both aqueous solution and gaseous forms A 10% aqueous solution is routinely used. Uses:
1) preservation of tissues for pathological examination2) To sterilize bacterial vaccines3) To prepare toxoid from toxin4) For killing of bacterial cultures and suspensions5) For destroying anthrax spores in hair and wool.
Dr.T.V.Rao MD 20
Glutaraldehyde :
• Effective against bacteria , fungi and viruses.• Less toxic and irritant to eyes and skin than
formaldehyde• Used as 2% buffered solution• Available commercially as CIDEX• Uses:
1. For sterilisation of cystoscopes, endoscopes and bronchoscopes
2. For sterilisation of plastic endotracheal tubes, face masks, rubber anesthetic tubes
Dr.T.V.Rao MD 21
Phenols:• Lister,the father of antiseptic surgery, first introduced
the use of phenol ( Carbolic acid) in surgery (1867).• Produced by distillation of coal tar between
temperatures of 170°C and 270°C.• Bactericidal action due to cell membrane damage.• Commonly used Phenol derivatives are
1. cresol 2. chlorhexidine 3. chloroxylenol 4. hexachlorophanes
Dr.T.V.Rao MD 22
Cresols :
• Lysol is a solution of cresols in soap.
• Active against a wide range of organisms.
• uses:1. For sterilisation of
infected glass ware2. Cleaning of floors3. Disinfection of excreta
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Chlorhexidine:
–Eg.Savlon – (Chlorhexidine and Cetrimide)
–More active against Gram positive than Gram negative
–Good fungicidal activity.–No action on spores and little activity
against viruses
Dr.T.V.Rao MD 24
Chloroxylenol :
–Eg.dettol–Less toxic and
less irritant.–Readily
inactivated by organic matter
–Inactive against pseudomonas.
Dr.T.V.Rao MD 25
Hexachlorophanes:
:• More active against Gram positive than Gram
negative bacteria.• Bacteriostatic at high dilutions.• Applied on skin as prophylaxis against
staphylococcal infections.• Potentially toxic and should be used with care.
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Halogens:
4.Halogens:i. Chlorine ii. Iodine
Commonly used disinfectants
Bactericidal, sporicidal and virucidal
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Chlorine : In the form of
Bleaching powder, Sodium hypochlorite Chloramine
Disinfection is due to release of free chlorine. Reacts with water to form hypochlorus acid . Bactericidal, viricidal, fungicidal and sporicidal. Used in water supplies, swimming pools, food
and dairy industries.
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Iodine :
• Used as skin disinfectant.
• Bactericidal and moderate action on spores.
• Betadine is one example.
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5.Oxidising agents:
Hydrogen peroxide• Effective at concentration of 3-6%• Kills spores at 10- 25%• Used to disinfect
»Contact lenses»Surgical prostheses»Plastic implants
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Salts:
• Salts of heavy metals have toxic effect on bacteria.
• Salts of copper, silver and mercury are used as disinfectants.
• Act by coagulation of bacterial proteins.• Mercuric chloride, once used as disinfectant is
highly toxic.• Thimersol and mercurochrome are less toxic • Copper salts are used as fungicides.
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Surface active agents:
• Substances which alter energy relationships at interfaces , producing a reduction of surface tension, are known as surface active agents or surfactants.– Anionic– cationic– nonionic – amphoteric compounds.
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The anionic compounds::
• e.g.:- common soaps, • Have strong detergent but weak
antimicrobial properties . • These agents are most active at acidic ph. • Effective against Gram positive
organisms but are relatively ineffective against Gram negative species.
Dr.T.V.Rao MD 33
Cationic surfactants::
• Quaternary ammonium compounds are the most important cationic surfactants.
• These compounds are bactericidal for a wide range of organisms, gram positive species are more susceptible.
• The common cationic compounds are acetyl trimethyl ammonium bromide (cetavalon or Cetrimide) and benzalkonium chloride.Dr.T.V.Rao MD 34
Amphoteric compounds:
Known as ‘Tego’ compounds possess detergent properties of anionic and antimicrobial activity of cationic compounds.
• They are active against a wide range of Gram positive and Gram negative organisms and some viruses.
Dr.T.V.Rao MD 35
Dyes ::• Two groups of dyes have been used extensively as
skin and wound antiseptics– aniline dyes – acridine dyes
• Both are bacteriostatic in high dilution but have low bactericidal action.
• Aniline dyes include crystal violet, brilliant green and malachite green.
• They are more active against Gram positive bacteria than Gram negative bacteria.
Dr.T.V.Rao MD 36
Dyes :
• Acridine dyes include acriflavine , euflavine, proflavine and aminacrine.
• They are more active against Gram positive bacteria than Gram negative bacteria.
• Gentian violet and acriflavine are two widely used dyes for skin disinfection especially in Gram positive bacterial infections.
Dr.T.V.Rao MD 37
Vapour phase disinfectants:
•Formaldehyde gas
•Ethylene oxide• Betapropiolactone
Dr.T.V.Rao MD 38
Formaldehyde gas:
• Used for fumigation of operation theatres, wards and laboratories etc.
• It is generated by adding 150 gm of KMnO4 to 280 ml of formalin for 1000 cu. Feet of room volume.
• The doors should be sealed and left unopened for 48 hours.
• The gas is toxic and irritant when inhaled.• After completion of sterilisation the irritant vapors
are nullified by exposure to ammonia vapor.
Dr.T.V.Rao MD 39
Ethylene oxide:
• It is a colorless liquid with a boiling point of 10.7°C.• Effective against all types of organisms including
viruses and spores.• It has a potential toxicity to human beings, including
mutagenicity and carcinogenicity .• It is highly inflammable.• Used for sterilizing plastic and rubber articles,
respirators, heart lung machines, sutures, dental equipment's etc.
Dr.T.V.Rao MD 40
Betapropiolactone :
• Condensation product of ketane and formaldehyde.
• It has a boiling point of 163°C.• Used in 0.2%.• Effective against all types of organisms
including viruses.• More efficient for fumigation than
formaldehyde.• Used for inactivation of vaccines.
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• Programme Created by Dr.T.V.Rao MD for Medical and Paramedical Students in
the Developing World • Email.com
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