This document summarizes sterilization and disinfection methods. It discusses sterilization as a process that eliminates all microorganisms, while disinfection only eliminates pathogens. Physical sterilization methods include heat, radiation, and filtration. Heat sterilization can be achieved through dry heat or moist heat above 100°C using an autoclave. Chemical disinfectants include alcohols, aldehydes, phenols, and halogens. An ideal disinfectant is broad-spectrum, fast-acting, stable, non-toxic, and inexpensive. Factors like concentration, temperature, and organic matter influence disinfectant potency.

1. STERILISATION AND
DISINFECTION
DR. AISHWARYA MARBATE

2.  Sterilisation: a process by which article, surface or
medium is made free of all microorganisms either
in the vegetative or spore form.
 Disinfection: means the destruction of all
pathogens or organisms capable of producing
infections but not necessarily spores.

3.  Antiseptics: chemical disinfectants which can
safely be applied to living tissues and are used to
prevent infection by inhibiting the growth of
microorganisms.
 Asepsis: The technique by which , the occurrence
of infection into an uninfected tissue is prevented.

4. Uses of Sterilisation/Disinfection
1. Sterilisation of materials, instruments
used in surgical and diagnostic
procedures. 2. For media and reagents
used in the microbiology laboratory.
3. In food and drug manufacturing to
ensure safety from contaminating
organisms.

5. METHODS OF STERILISATION
A. Physical
methods
1. Sunlight
2. Heat /
(a ) Dry heat
(b) Moist heat
3. Ozone
4. Filtration
5. Radiation
B. Chemical Methods
1. Alcohols
2 . Aldehydes
3. Phenols
4 . Halogens
5 . Oxidising agents
6. Salts
7 . Surface active agents
8. Dyes
9 . Vapour phase disinfectan

6. HEAT
Principle:
(i) Dry heat kills the organisms by
denaturation of bacterial protein,
oxidative damage and by the toxic
effect of elevated levels of
electrolytes.
(ii) Moist heat kills the microorganisms
by denaturation and coagulation of
proteins.

7. Factors influencing :
(i) Nature of heat: Dry heat or moist
heat
(ii) Temperature and duration
(iii) Characteristic of microorganisms
and spores present
(iv) Type of material

8. DRY HEAT STERILISATION
(i) Red heat- inoculating wire loops, tips
of forceps and needles
(ii) Flaming- Glass slides, scalpels and
mouths of culture
(iii) Incineration-By this method,
infective material is reduced to ashes by
burning. Soiled dressing, bedding and
pathological material.

9. (iv) Hot air oven-The oven is electrically
heated and is fitted with a fan to ensure
adequate and even distribution of hot air
in the chamber.

10.  Most widely used method.
 160 degreeC for 2 hrs
 USES- 1) Glasswares like glass syringes,
petridishes, flasks, pipettes and test tubes
(ii) Surgical instruments like scalpels
(iii) Chemicals such as liquid paraffin, fats,
sulphonamides powders.

11.  Precautions
(i) not be overloaded .
(ii) free circulation of air.
(iii) Material to be sterilised should be perfectly dry .
( vi) Rubber or any inflammable material should not
be kept inside the
( vii) The oven must be allowed for two hours
before opening the doors, since the glasswares
may crack by sudden cooling

12. MOIST HEAT STERILISATION
(i) At a temperature below 100°C
(ii) At a temperature of 100°C
(iii) At a temperature above 100°C

13. Below 100°C
1. Pasteurisation of milk: Two types of method,
holder method (63°C for 30 minutes) and
flash method (72°C for 20 seconds followed
by cooling quickly to l3°C or lower).
2. Inspissation: by heating at 80-85°C
temperature for half an hour daily on three
consecutive days
3. Vaccine bath: Bacterial vaccines are
sterilised in special vaccine baths at 60°C
for one hour.

14. At 100°C
1. Boiling: Boiling for 10 to 30 minutes may
kill most of the vegetative forms but not
spores.
2. Tyndallisation- Steam at 100°C for 2o
mins on three successive days
3. Steam steriliser: 100°C for 90 mins

16. Above 100°C (under pressure)
 At normal pressure water boils at
100°C but when pressure inside a
closed vessel increases, the
temperature at which water boils also
increases. This principle has been
applied in autoclave and pressure
cooker .

17. AUTOCLAVE
 Principle:
Steam above 100°C or saturated steam
has better killing power than dry heat.
Bacteria are more susceptible to moist
heat as bacterial protein coagulates
rapidly. Saturated steam can penetrate
porous material easily.

19. Components:
 Autoclave is a modified pressure cooker or
boiler.
 A vertical or horizontal cylinder of gunmetal
or stainless steel in 'a supporting iron case.
 The lid is fastened by screw clamps and
rendered air tight by an asbestos washer.
 The lid bears a discharge tap for air and
steam, a pressure gauge and a safety valve.
 Heating is done by electricity.

21.  Sterilisation conditions
 Temperature - 121 °C
 Chamber pressure - 15 lb per square
inch
 Holding time - 15 minutes

22.  Uses
(i) To sterilise culture media rubber
material, gowns, dressing, gloves etc.
(ii) It is particularly useful for materials
which cannot withstand the higher
temperature of hot air oven .
(iii) For all glass syringes, hot air oven is
a better sterilising method.

23.  Sterilisation control :
(i) Thermocouple
(ii) Bacterial spores: Spores of bacillus stearo-
thermophilus are used as the test organism .
This organism has an optimum growth
temperature of 55- 60 °C and its spores are
killed in 12 minutes at 121 °C.
(iii) Chemical indicators
(iv) Autoclave tapes

24. FILTRATION
 This method of sterilisation is useful for
substances which get damaged by heat
process.
 Uses:
(i) sterilise sera, sugars and antibiotic
solutions.
(ii) Separation of toxins and bacteriophages
from bacteria.
(iii) To obtain bacteria free filtrates
(iv) Sterilisation of hydatid fluid.
(v) Purification of water.

25.  Limitation: retains bacteria but allows
viruses and mycoplasms to pass
 Types:
(i) Candle filters
(ii) Asbestos disc fliters e.g. Seitz filter
(iii) Sintered glass filte
(iv) Membrane filters
(v) Air filters
(vi) Syringe filters

26. B. Chemical Methods
 An ideal antiseptic or disinfectant should
(i) have wide spectrum of activity and be effective
against all microorganisms including bacteria (both
vegetative and spore forms), viruses, protozoa and
fungi,
(ii) act in the presence of organic matters,
(iii) have high Penetration power and quick action,
(iv) be stable and effective in acidic as well as in
alkaline
conditions,
(v) not corrode metals,
(vi) be compatible with other disinfectants,
( vii) not cause local irritation,
( viii) not be toxic if absorbed into circulation,
(ix) be safe and easy to use, and
(x) be easily available and cheap .

27.  The following factors influence the potency of
a disinfectant :
(i) concentration
(ii) time of action
(iii) pH
(iv) temperature
(v) nature of organism and
( vi) presence of organic matter

28.  Disinfectants can be divided into three
groups:
1) High level disinfectants.
 e.g glutaraldehyde, hydrogen peroxide
paracetic acid and chlorine compounds.
2) Intermediate level disinfectants.
E.g alcohols, iodophores and phenolic
compounds
3) Low level disinfectants.

30. THANK YOU