Sterilization is the process of removing or destroying all forms of microorganisms like bacteria, fungi and viruses. It uses physical, chemical and mechanical methods to destroy microbes. Physical methods include heat sterilization using moist heat (autoclaving) or dry heat. Radiation sterilization uses gamma rays, x-rays or UV light. Chemical sterilization employs gases like ethylene oxide or liquids like alcohol and phenol. Proper sterilization is essential for disinfecting medical equipment and surgical tools to prevent infection.

1. STERILIZATION

2. WHAT IS
STERILIZATION?
• Sterilization can be defined as a process by which all
viable forms of micro-organisms(such as fungi, bacteria,
viruses) are removed or destroyed.
• Micro organisms are present at everywhere. Since they
cause contamination, infection, and decay, it becomes
necessary to remove or destroy them from materials or
from areas.
• Sterilization procedures used is should be simple but
effective and of relatively short duration.
• It causes denaturation of proteins nucleic acids and
components of cellular membrane.

3. METHODS OF STERILIZATION
(1)Physical
(2)Chemical
(3)Filtration (Mechanical)

4. Physical methods
• •
1) Sunlight
2) Drying
3) Heat:- i) Moist heat
ii) Dry heat
4) Radiation
5) Autoclave

5. 1) Sun light - It is responsible for spontaneous sterilization in natural
conditions.
In tropical countries, the sunlight is more effective in killing germs
due to combination of ultraviolet rays and heat.
By killing bacteria suspended in water, sunlight provides natural
method of disinfection of tanks and lakes.
2) Drying - Moisture is essential for growth of bacteria.
Drying in air has dangerous effect on many bacteria.
However, spores are unaffected.
Therefore, it is not satisfactory method for sterilization.

6. 3) Heat sterilization- it is of two types :
4) Incineration
A)Dry heat sterilization- In dry heat sterilization, dry heat is used for
sterilizing different materials. Heated air or fire is used in this process. As
compared to the moist heat sterilization, the temperature is higher. The
temp. is maintained for almost an hour to kill the most difficult of the
resistant spores.
Dry heat sterilization also have 4 type:- 1) Hot air oven
2) Red hot sterilization
3) Flaming

7. 1) Hot air oven:- Hot air ovens are electrical devices which use dry
heat to sterilize. They were originally developed by pasteur.
 Generally, they can be operated from
50 to 300 °C, using a thermostat to control
the temperature. ... An air circulating fan
helps in uniform distribution of the heat.
2) Red hot sterilization:- Sterilization by holding them in
Bunsen flame till they become red hot. It use for
bacteriological loops, straight wires, tips of
forceps & spatulas

8. 3) Flaming:- This is a method of passing article
over a flame, but not heating it to redness.
Use- scalpels, mouth of test tubes,
flask, glass slide & coverslips
4) Incineration:- Incineration is a waste treatment process that
involves of organic substances contained in waste materials.
This method also burns any organism to ash.
It is used to sterilize medical and other
biohazardous waste before it is discarded
with non-hazardous waste
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9. B) Moist heat sterilization :- Moist heat method is used for heat
sensitive materials and materials through which steam is permeable.
culture media is also sterilized through moist heat sterilization.
It has also 3 types:- 1) Below 100°C 2) Above 100°C 2) At 100°C
1) Below 100°C:- It has also 2 types
i) Pasteurization- Its purpose is to reduce the bacterial
population of a liquid such as a milk & destroy
Organism that may cause spoilage.
Spores are not affected by this method.

10. ii) inspissation:- Heating at 80-85°C for half an
hour daily on three consecutive days.
Serum or egg media are sterilized.
2) At 100°c:- It has also 2 types.
i) Boiling:-Boiling is a very simple method of water disinfection.
Heating water to a high temperature, 100°C, kills most of the
pathogenic organisms, particularly viruses and bacteria causing
waterborne diseases. In order for boiling to
be most effective, the water must boil for at
least 20 minutes.

11. ii) Tyndallization:- Exposure at 100°C for 20-45
minutes for 3 successive days. Used for sterilizing
sugars, gelatin, & serum containing media.
3) Above 100°C:-
Autoclave:-
 Autoclaving is the most reliable method for sterilization.
Autoclave use pressurized steam to destroy microorganism, and are
the most dependable system available for the decontamination of
laboratory waste & the sterilization of glass wares, media, & reagents.

12. For efficient heat transfer, steam must flush the air out of the
autoclave chamber.
Generally the conditions employed are temperature up to 121-134°
for 15-20 minutes under 15 lbs pressure.
The condition based on the type of the
material used for sterilization.

13. Autoclave
principle:
• The autoclave works on the
principle of moist heat
sterilization where steam
under pressure is used to
sterilize the material present
inside the chamber.
• The high pressure increases
the boiling point of water and
thus helps achieve a higher
temperature for sterilization.

14. Autoclave
principle:
• Water usually boils at 100°C under normal atmospheric pressure (760 mm of Hg).
• When this steam comes in contact on the surface, it kills the microbes by giving off latent heat.
• The condensed liquid ensures the moist killing of the microbes.
• The pressure inside the chamber is then restored back tot eh ambient pressure while the
components inside remain hot for some time.
• Types of autoclave:
• Pressure cooker type/ Laboratory bench autoclaves (N-type)
• These, as domestic pressure cookers, are still in use in many parts of the world.
• The more modern type has a metal chamber with a secure metal lid that can be fastened and sealed
with a rubber gasket.
• It has an air and steam discharge tap, pressure gauge, and safety valve. There is an electric
immersion heater in the bottom of the chamber.
• Gravity displacement type autoclave
• This is the common type of autoclave used in laboratories.
• In this type of autoclave, the steam is created inside the chamber via the heating unit, which then
moves around the chamber for sterilization.
• This type of autoclave is comparatively cheaper than other types.

15. Positive pressure displacement type (B-type)
•In this type of autoclave, the steam is generated in a separate steam
generator which is then passed into the autoclave.
•This autoclave is faster as the steam can be generated within seconds.
•This type of autoclave is an improvement over the gravity displacement
type.
Negative pressure displacement type (S-type)
•This is another type of autoclave which contains both the steam generator
as well as a vacuum generator.
•Here, the vacuum generator pulls out all the air from inside the autoclave
while the steam generator creates steam.
•The steam is then passed into the autoclave.
•This is the most recommended type of autoclave as it is very accurate and
achieves a high sterility assurance level.
•This is also the most expensive type of autoclave.

16. Uses of autoclave
• They are used to decontaminate specific
biological waste and sterilize media,
instruments, and labware.
• Regulated medical waste that might
contain bacteria, viruses, and other biological
materials are recommended to be inactivated
by autoclaving before disposal.
• In medical labs, autoclaves are used to
sterilize medical equipment, glassware,
surgical equipment, and medical wastes.
• Similarly, autoclaves are used for the
sterilization of culture media, autoclavable
containers, plastic tubes, and pipette tips.

17. 4) Radiation sterilization:-
It has 2 types.
• Non-ionizing(Hot sterilization):-
• Infrared rays- used for rapid mass
sterilization of prepacked items such as
syringe, catheters( a thin tube that is put
into the body in order to remove liquids)
• U.v. rays- used for disinfecting enclosed
area such as entry ways, operation theatres
& labs.
• Wl = 230-280nm,typically 254nm.

18. Benefits of UV Light for Sterilization
• UV light sterilization is an environmentally friendly method of killing bacteria, mold,
fungi, and viruses without the use of harmful chemicals and does not produce
corrosive materials or disinfection by-products (DBPs). There are many industries
where surface disinfection without the use of chemicals is critical and UV light
sterilization can provide a safe, effective solution. UV disinfection and sterilization
systems are proven to be:
• Highly effective
• Cost-efficient
• Low maintenance
• Chemical free
• UV lamps used are used in a multitude of industries and applications, providing vital
solutions to improve the health and wellness of people in residential, commercial and
industrial settings. It is used to disinfect the air of transmissible agents, fungi, bacteria,
viruses, dust mites and spores.

19. UV
Sterilization
Improves
Health in
Many
Industries
• Food Industry – UV lamps are used for irradiation. Ultraviolet
light sterilization kills viruses, bacteria, yeast and fungi in
seconds, and can also extend shelf life and nutritional value.
Food applications include packaging materials, conveyor
belts.
• Industrial Air Purification – UV lamps are used to remove
harmful or toxic chemicals produced in many industries and
to reduce or eliminate VOCs and industrial exhausts
containing solvents.
• Water Sterilization – UV light sterilization is highly effective
at eliminating many harmful pathogens from water and kills
some bacteria that chlorine does not. UV water disinfection
systems are utilized to purify drinking water,
• Surface Sterilization – UV lamps are used in many
environments such as restaurants to sterilize kitchen
equipment and surfaces, hospitals to sterilize medical
equipment, food buffets and many other environments where
surface sterilization improves public health.

20. • Ionizing(Cold sterilization):-
• Gamma rays & X-rays:- Used for
sterilizing plastics, syringes, swabs, animal
feeds, oils, greases, fabric & metal foils
• Advantages of radiation sterilization:-
clean & dry process,
ensure full exposure of object from all
direction.
• Disadvantages:- posses
threat to human,
lengthy process, requires
very qualified person

22. Chemical methods
1) Gaseous sterilization:- i) Ethylene oxide
ii) Formaldehyde gas
2) Liquid sterilization:- i) Alcohol
ii) Phenol

23. 1) Gaseous sterilization
• i. Ethylene oxide:- EtO sterilization is mainly use to sterilize
medical & pharmaceutical products that can not support
conventional high temperature steam sterilization- such as
devices that incorporate electronic components, plastic
packaging or plastic container.
• This method uses automatic device filled with ethylene oxide
gas
• at temperature below 100°C to sterilize complex & delicate
material.
• EtO destroys microorganism by chemically reacting with
nucleic acid.

24.  Advantages :- Fully automatic, high efficiency, 100% result
Disadvantages:-Complex and time consuming process,
carcinogenic safety concern
ii. Formaldehyde gas:-Another low temperature method for
sterilizing heat sensitive items is formaldehyde sterilization.
Formaldehyde is an organic chemical compound which is a by-
product of the metabolism of many organisms and is commonly
found in fresh air, rainwater, foods, industrial products and fabrics.
It is considered even more dangerous than EtO and is therefore
less commonly used for sterilization.

25. Formaldehyde sterilization is used where sterilization by steam
or high temperature is not possible.
Formaldehyde is soluble in water and its inactivation power is
greatly improved by the presence of humidity. It is most
commonly used as a disinfectant, but sometimes formaldehyde
is used as a sterilizing agent. The process is known as low
temperature steam and formaldehyde (LTSF)

26. Advantages:- Very reactive molecule, Faster cycle time
compared to EtO, cost per cycle is lower than EtO, after
sterilization most loads are available for immediate use
Disadvantages:- The vapour is extremely irritating to the
eyes, weak penetrating power compared to EtO, operates on
a higher temperature than EtO, formaldehyde residue can
remain on the sterilized goods if the rinsing phase is not
100% efficient. This can be harmful for the patients

27. 2) Liquid sterilization
water.
i) Alcohol:- Alcohols are effective disinfectants for many reasons.
They evaporate quickly, without leaving a residue. They are capable
of dissolving lipids, which makes them effective against lipid-wrapped
viral cells such as HIV and hepatitis A. They are inexpensive and
relatively easy to handle, although their vapors are flammable.
Ethanol and isopropyl alcohol are both members of the alcohol
family and have similar disinfectant properties. Ethanol is the type of
alcohol present in alcoholic beverages. Isopropyl alcohol is also
known as isopropanol, 2-propanol or rubbing alcohol. When used as
disinfectants, both are typically at a concentration of 70 percent in

28. ii) Phenols:- Phenol is one of the oldest antiseptic agents.
phenols acts by damaging cell membrane thus releasing cell
contents & causing lysis.
phenols is commonly found in mouth washes, scrub soaps, &
surface disinfectants.
phenols are used for decontamination of the hospital
environment, including laboratory surfaces, & non critical
medical items.
Examples:-

29. Filtration (Mechanical) methods
Filtration sterilization used for heat sensitive materials to sterilize.
Filtration process does not destroy but removes the microorganisms.
Filtration allows for the exclusion of organisms based upon size.
Procedure:- The solution to be sterilized is passed through the filter
and collected in the sterile receiver by the application of positive
pressure to the nonsterile compartment or negative pressure to the
sterile slide.

30. Mode of action
• The filters are thought to function by one or usually a combination of the following:
• Sieving or screening
• Entrapment
• Electrostatic attraction
• When a particle is larger than the pore size of the filter the particle is retained on the filter-
this known as sieving or screening

31. Entrapment occurs when a particle smaller than the size of the pore
enters into the pore channel and lodges onto the curves of the
channel while passing through it.
In Electrostatic attraction Particles are attracted & absorbed at the
surface of the filter bed which is oppositely charged.
There are 4 types of filters:-
1. Membrane filters
2. Sintered or Fritted glass filters
3. Seitz filters
4. Ceramic filters

32. 1) Membrane filters:- They are made of cellulose-derivative (acetate or
nitrate). They are very fine. They are fixed in some suitable holders.
• Nominal pore size is 0.22 ± 0.02mm or less
is required.
• The membranes are brittle when dry. In
this condition they can be
• stored for years together. They become very
tough when dipped in water.
• They are suitable for sterilizing aqueous
and oily solutions but not
• for organic solvents such as alcohol,
chloroform etc.

33.  They are sterilized by autoclaving or by ethylene oxide gas.
They can not be sterilized by dry heat as they decompose
above 130°C.
 Membrane filters are generally blocked by dirt particles and
organisms. Pre-filtration (through glass-fibre paper prefilter)
reduces the risks of membrane filter.
Examples:- i) MF-Milipore - it is a mixture of cellulose esters
ii) Sartorius regular – it is made of cellulose nitrate

35. 2) Sintered (or Fritted) glass filters:-
 Borosilicate glass is finely powdered in a ball-mill and the particles
of required size are separated.
 This is packed into disc mounted and heated till the particles get
fused. The disc thus made have pore size of 2 mm and are used
for filtration.
 They are cleaned with the help of sulfuric acid.

36. 3) Seitz filters:-
 It consists of two parts.
 Lower part filled with a perforated plate over which
compressed asbestos pad is placed.
 Upper part has a valve through which pressure can be
applied.
 Both parts joined together by winged nuts.
 The main advantage of this filter is that no
risk of contamination & easy to use.
 For viscous solution they are more suitable.

37. • 4) Ceramic filters:-
• Ceramic water filters are an inexpensive and
effective type of water filter, that rely on the
small pore size of ceramic material to filter dirt,
debris, and bacteria out.
• However, filters are typically not effective
against viruses since they are small enough to
pass through to the "clean" side of the filter.
• Ceramic filtration does not remove chemical
contaminants.
• However, some manufacturers (especially of
ceramic candle filters) incorporate a high-
performance activated carbon core inside the
ceramic filter that reduces organic and
metallic contaminants.

38. The two most common types of ceramic water filter are pot-type
and candle-type filters.

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