bds second year

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Disinfection

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Disclaimer
• Some of the contents of this subject has been
sourced from web sources and books
• REFERENCES
- Textbook of Microbiology. Ananthnarayan &
Paniker. 9th edition
- www.google.com
The Content is only for educational purpose

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Intended learning Objectives
• To enumerate the compounds used as
disinfectants
• To explain the mechanism of action
• To list the limitations of disinfectants
• Mention the methods for testing of disinfectant

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CONTENTS
• Definition & Properties
• Phenols
• Alcohol
• Oxidizing agents
• Dyes
• Aldehydes
• Testing of disinfectants

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Disinfectants
Chemical agents used for the purpose of
disinfection

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Properties
• Generally toxic & skin irritants
• More effective against Gram positive bacteria
• Concentration dependant
• Expiry date
• Inactivation due to organic substances
• Reduced activity along with cleaning agents

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Phenols
• Phenol (1%), Cresol, hexa chlorophene,
chlorhexidine
• Cell membrane damage & precipitation of
proteins
• Phenol
– Acts on vegetative forms of bacteria, TB, certain fungi
– Excellent disinfectant for faeces, blood, pus, linen
– Corrosive nature

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Phenol derivatives
• Cresol
– More germicidal but corrosive to tissue
– Cleaning floors, instruments, glassware
– Does not inactivate HBV, HIV
• Hexachlorophene
– Used in germicidal soaps
• Chlorhexidine
– Highly effective against Gram positive & Gram
negative
– Skin antiseptic, bladder irrigant

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Alcohols
• Ethyl alcohol (70%), Isopropyl alcohol,
methylated spirit
• Acts by denaturation of proteins
• Used as skin antiseptics
• Active against both Gram positive & Gram
negative
• No action against spores / viruses
• Methylated spirit can be used for cleaning
cabinets, incubators – active against fungal
spores

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Oxidizing agents
• Halogens, H2O2, Potassium permanganate
• Inactivation of sulphydryl groups in enzymes
• Chlorine
– Disinfection of water, dairy equipments, sanitary
utensils
– Very effective against gram positive, gram negative, TB,
HBV, HIV even in presence of serum
– Corrosive to metals, textiles

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• Iodine
– Commonly used skin antiseptic in medical practice
– Skin irritant – hence should be cleaned with
alcohol
• H2O2
– Weak disinfectant used for wound antisepsis
• KMnO4
– Powerful oxidizing agent used in treatment of
urethritis
– Active against bacteria & viruses

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Dyes
Aniline dyes Acridine dyes
• Crystal violet, Gentian violet,
malachite green
• Gram postive
• Inhibited by organic material
• Binds to phosphate
• Used in microbiology
• Proflavin, Acriflavin
• Gram positive & gram negative
• Not affected by presence of
organic matter
• Binds to DNA
• Dressing wounds

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Aldehydes
• Formaldehyde (10%), Gluteraldehyde (2%)
• Denaturation of proteins
• Formaldehyde is most effective sterilant – kills all
living forms including spores
– Room sterilization – OT
– Corrosive to rubber
• Gluteraldehyde used for sterilization of
endoscopes

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Metallic salts & surface active agents
• Salts of silver, copper mercury
– Fungicidal but bacteriostatic
• Wetting agents, detergents & emulsifiers
– Disruption of cell membrane
– Cationic, nonionic, amphoteric
– Cetavlon / cetrimide

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Testing of disinfectants
• Ridael walker test
• Chick martin test
• Kelsy sykes test
• In use test
• Principle – indicator bacteria + exposure to
disinfectant for specified time period with or
without organic matter

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Summary
• Chemical that are used to kill microorganisms in
their vegetative state
• They belong to alcohols, alkali, halogens, dyes etc
• They can be used for skin disinfection as well as
inanimate surface disinfection
• There are few tests to asses the quality of
disinfectants