This document discusses sterilization and disinfection using chemicals. It begins by explaining why sterilization is needed to remove or destroy microorganisms that can cause infection. It then discusses various chemical methods used for sterilization and disinfection, including alcohols, aldehydes, phenols, halogens, oxidizing agents, salts, and others. It provides details on specific chemicals like formaldehyde, glutaraldehyde, chlorhexidine, iodine, and hydrogen peroxide. It also covers factors that influence the efficacy of disinfection like contact time, temperature, and type of microorganism. The document aims to provide information on proper sterilization and disinfection using chemical methods.

1. DISINFECTION
by chemicals
basics
Dr.T.V.Rao MD
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2. 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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3. 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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4. How can microorganisms
be killed?
 Denaturation of proteins (e.g. wet heat, ethylene
oxide)
 Oxidation (e.g. dry heat, hydrogen peroxide)
 Filtration
 Interruption of DNA synthesis/repair (e.g.
radiation)
 Interference with protein synthesis (e.g. bleach)
 Disruption of cell membranes (e.g. phenols)
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5. Factors that influence efficacy of
disinfection/sterilization


3
4
5
6
7
Contact time
Physico-chemical environment (e.g. pH)
Presence of organic material
Temperature
Type of microorganism
Number of microorganisms
Material composition
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6. Relative Resistance of Microbial
Forms
Highest resistance
Moderate resistance
Least resistance
bacterial endospore
(Bacillus & Clostridium)
protozoan cyst
some fungal spores
some naked virus
vegetative bacteria that
have higher resistance
( M. tuberculosis, S.aureus,
Pseudomonas)
most bacterial vegetative cells
ordinary fungal spores & hypae
enveloped virus
Yeasts
Trophozoites
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7. 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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8. 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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9. 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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10. Number of living microbes
Figure 9.1 A plot of microbial death rate
Constant percentage
of the extant population
is killed each minute
90% die
1 min
90% die
1 min
Time (min)
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11. Chemical Methods
Many matters, substances and
objects cannot be sterilized with
Physical methods
So Need for Disinfectants
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12. Chemical methods
•
•
•
•
•
•
•
•
•
Alcohols
Aldehydes
Phenols
Halogens
Oxidizing agents
Salts
Surface active agents
Dyes
Vapour phase disinfectants
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13. 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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14. Levels of Disinfection
1. High level
disinfectants
2. Intermediate
level
disinfectants
3. low level
disinfectants
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15. 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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16. Intermediate level disinfectants
•
•
•
May not effective
against spores
Includes alcohols,
iodophores and
phenols
Used for:
– Laryngoscopes
– Fiber optic
endoscopes
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17. 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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18. 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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19. Aldehydes:
2.
a) Formaldehyde
b) Glutaraldehyde
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20. Formaldehyde:




Bactericidal, sporicidal and virucidal
Used in both aqueous solution and gaseous forms
A 10% aqueous solution is routinely used.
Uses:
1)
2)
3)
4)
5)
preservation of tissues for pathological examination
To sterilize bacterial vaccines
To prepare toxoid from toxin
For killing of bacterial cultures and suspensions
For destroying anthrax spores in hair and wool.
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21. 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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22. 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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23. Cresols :
•
•
•
Lysol is a solution of
cresols in soap.
Active against a wide
range of organisms.
uses:
1. For sterilisation of
infected glass ware
2. Cleaning of floors
3. Disinfection of excreta
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24. 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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25. Chloroxylenol :
–Eg.dettol
–Less toxic and
less irritant.
–Readily
inactivated by
organic matter
–Inactive against
pseudomonas.
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26. 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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27. Halogens:
4.Halogens:
i. Chlorine
ii. Iodine
 Commonly used
disinfectants
 Bactericidal,
sporicidal and
virucidal
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28. 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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29. Iodine :
• Used as skin
disinfectant.
• Bactericidal and
moderate
action on
spores.
• Betadine is one
example.
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30. 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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31. 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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32. 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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33. 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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34. :
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.
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35. 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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36. 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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37. 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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38. Vapour phase disinfectants:
• Formaldehyde
gas
• Ethylene oxide
• Betapropiolactone
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39. 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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40. 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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41. 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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