1. DISINFECTION
by chemicals
basics
Dr.T.V.Rao MD
Dr.T.V.Rao MD 1

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.
Dr.T.V.Rao MD 2

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.
Dr.T.V.Rao MD 3

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)
Dr.T.V.Rao MD 4

5. Factors that influence efficacy of
disinfection/sterilization
 Contact time
 Physico-chemical environment (e.g. pH)
3 Presence of organic material
4 Temperature
5 Type of microorganism
6 Number of microorganisms
7 Material composition
Dr.T.V.Rao MD 5

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
Dr.T.V.Rao MD 6

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.
Dr.T.V.Rao MD 7

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.
Dr.T.V.Rao MD 8

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
Dr.T.V.Rao MD 9

10. Figure 9.1 A plot of microbial death rate
Dr.T.V.Rao MD 10
90% die
1 min
90% die
1 min
Constant percentage
of the extant population
is killed each minute
Time (min)
Number of living microbes

11. Chemical Methods
Many matters, substances and
objects cannot be sterilized with
Physical methods
So Need for Disinfectants
Dr.T.V.Rao MD 11

12. Chemical methods
• Alcohols
• Aldehydes
• Phenols
• Halogens
• Oxidizing agents
• Salts
• Surface active agents
• Dyes
• Vapour phase disinfDer.Tc.V.tRaao nMDts 12

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
Dr.T.V.Rao MD 13

14. Levels of Disinfection
1. High level
disinfectants
2. Intermediate
level
disinfectants
3. low level
disinfectants
Dr.T.V.Rao MD 14

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
Dr.T.V.Rao MD 15

16. Intermediate level disinfectants
• May not effective
against spores
• Includes alcohols,
iodophores and
phenols
• Used for:
– Laryngoscopes
– Fiber optic
endoscopes
Dr.T.V.Rao MD 16

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.
Dr.T.V.Rao MD 17

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.
Dr.T.V.Rao MD 18

19. Aldehydes:
2.
a) Formaldehyde
b) Glutaraldehyde
Dr.T.V.Rao MD 19

20. 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 examination
2) To sterilize bacterial vaccines
3) To prepare toxoid from toxin
4) For killing of bacterial cultures and suspensions
5) For destroying anthrax spores in hair and wool.
Dr.T.V.Rao MD 20

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
Dr.T.V.Rao MD 21

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
Dr.T.V.Rao MD 22

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
Dr.T.V.Rao MD 23

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
Dr.T.V.Rao MD 24

25. Chloroxylenol :
–Eg.dettol
–Less toxic and
less irritant.
–Readily
inactivated by
organic matter
–Inactive against
pseudomonas.
Dr.T.V.Rao MD 25

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.
Dr.T.V.Rao MD 26

27. Halogens:
4.Halogens:
i. Chlorine
ii. Iodine
 Commonly used
disinfectants
 Bactericidal,
sporicidal and
virucidal
Dr.T.V.Rao MD 27

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.
Dr.T.V.Rao MD 28

29. Iodine :
• Used as skin
disinfectant.
• Bactericidal and
moderate
action on
spores.
• Betadine is one
example.
Dr.T.V.Rao MD 29

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
Dr.T.V.Rao MD 30

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.
Dr.T.V.Rao MD 31

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.
Dr.T.V.Rao MD 32

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.
Dr.T.V.Rao MD 33

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 chDlr.To.V.rRaiod MDe. 34

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.
Dr.T.V.Rao MD 35

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.
Dr.T.V.Rao MD 36

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.
Dr.T.V.Rao MD 37

38. Vapour phase disinfectants:
•Formaldehyde
gas
•Ethylene oxide
• Betapropiolactone
Dr.T.V.Rao MD 38

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.
Dr.T.V.Rao MD 39

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.
Dr.T.V.Rao MD 40

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.
Dr.T.V.Rao MD 41

42. • Programme Created by Dr.T.V.Rao MD
for Medical and Paramedical Students in
the Developing World
• Email.com
• doctortvrao@gmail.com
Dr.T.V.Rao MD 42