DISINFECTIONby chemicals

basicsDr.T.V.Rao MD

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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.

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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.

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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)

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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

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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

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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.

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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.

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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

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Figure 9.1 A plot of microbial death rate

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90% die

1 min

90% die

1 min

Constant percentageof the extant populationis killed each minute

Time (min)

Nu

mb

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livin

g m

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Chemical Methods

Many matters, substances and objects cannot be sterilized with

Physical methods So Need for Disinfectants

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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

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Levels of Disinfection1. High level

disinfectants2. Intermediate

level disinfectants

3. low level disinfectants

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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

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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.

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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.

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Aldehydes:2.

a) Formaldehydeb) Glutaraldehyde

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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.

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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

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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

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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

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Chloroxylenol :

–Eg.dettol–Less toxic and

less irritant.–Readily

inactivated by organic matter

–Inactive against pseudomonas.

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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.

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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.

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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.

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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.

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Vapour phase disinfectants:

•Formaldehyde gas

•Ethylene oxide• Betapropiolactone

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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.

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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.

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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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