A detail introduction and notes on Sterilization and different types of its methods

1. By :- Siddharth Kumar Sahu

2. • Sterilization and Terminologies
• Thermal Resistance of Micro-organism.
• Methods of sterilization
• Dry Heat Sterilization.
• Moist Heat Sterilization
• Radiation Sterilization.
• Filtration Sterilization.
• Chemical Method of sterilization.
• Gaseous Sterilization.

3. • Sterilization can be defined as any process that effectively kills or
eliminates transmissible agents (such as fungi, bacteria, viruses and
prions) from a surface, equipment, foods, medications, or biological
culture medium.
OR
• Sterilization refers to any process that eliminates, removes, kills, or
deactivates all forms of life and other biological agents like prions
present in a specific surface, object or fluid, for example food or
biological culture media.
OR in short.....
• It is a process of complete destruction of all microorganisms present in a
system and the products free from living organisms are called Sterile

4.  Disinfection: it is a process that eliminates many or all pathogenic
microorganisms, except bacterial spores.
o Different disinfectants have different target ranges, not all
disinfectants can kill all microorganisms.
 Antiseptic: not a disinfectant. It is a substance or product which
prevent the growth of microorganisms by inhibiting their activity
without destroying them.
 Sanitization: A process that reduces the level of micro organisms
count on eating and drinking utensils.

5.  Decontamination: Decontamination removes pathogenic
microorganisms from objects so they are safe to handle, use,
or discard.
 Aseptic: Free from contamination caused by harmful bacteria,
viruses, or other microorganisms; surgically sterile or sterilized.
 Aseptic processing is a processing technique where
thermally sterilized liquid products (typically food
or pharmaceutical) are packaged into previously sterilized
containers under sterile conditions to produce shelf-stable
products that do not need refrigeration.

6. • Heat(thermal) is lethal to microorganisms, but each species has
its own particular heat tolerance. And resistant of heat is varies
according to the method of sterilization.
• Before selecting any method for sterilization , first know the
condition & method that must be lethal to microorganisms &
spores. So, following points should be note…
1. Thermal Death Time
2. Death Rate of Microorganisms
3. Decimal Reduction Time ( D Value)

7. • It is defined as the time required to kill a specific micro-
organisms at a given temperature under specific
condition.
• Thermal death time depends on factors like-
I. Temprature
II. pH
III. Presence of Bactericide
IV. No. of Microorganisms
V. Resistance to Heat.
The rate at which a given microbe dies from treatment is
constant, but the time required to kill all organisms present
increases with population size or density.

8. • In this method of final death rate of microorganism is to plot
graph between survivor against time of exposure.
• It is defined as time (in minutes) required to reduce the number
of viable microorganisms by 90%. A ‘D-value’ is denoted with the
capital letter "D".
• The order of death of microorganisms can be calculated by
following eq.
K = 1/t (log No – log N)
• Where, K = Constant
t = time of exposure in minute
No = Number of viable organism in the beginning
N = Number of viable organism at the end.

9. Physical
Method
Chemical
Method
Mechanic
al Method
Sterilizatio
n Methods
Dry Heat Sterilization
Moist Heat Sterilization
Radiation Sterilization
Liquid Material
Gaseous Material
Sintered Glass Filters
Sintered Metal Filters
Membrane Filters

11. • Heat Sterilization -
• Dry Heat Sterilization. E.g.- Hot Air Oven.
• Moist Heat Sterilization. E.g.- Autoclave.
• Radiation Sterilization. E.g.- Electromagnetic Rays
• Filtration Sterilization. E.g.- Membrane, Sintered Glass.
Heat Sterilization
• It involving destruction of enzymes and other essential cell
constituents.
• This method of sterilization can be applied only to the thermo-
stable products, and this process is more effective in hydrated
state(moist).
• It can be used for moisture-sensitive materials for which dry
heat (160-180°C) sterilization is applied.
• For moisture-resistant materials for which moist heat(121-

12. Hot Air Oven-
• Dry heat sterilization is usually carried out in a hot air oven, which
consists of the following:
I. An insulated chamber surrounded by an outer case containing
electric
II. heaters.
III. A fan
IV. Shelves/trays
V. Temprature control knob
VI. Thermometer
VII. Door locking controls.

13. • Different temperature-time relations for holding time are
• 60 minutes at 160°C, 40 minutes at 170°C and
• 20 minutes at 180°C.
• Increasing temperature by 10 degrees, shortens the sterilizing time by 50
percent.
• The heat is transferred to the article by radiation, conduction and convection.
o Operation-
• (i) Articles to be sterilized are first wrapped or enclosed in containers of
cardboard, paper or aluminium.
• (ii) Then, the materials are arranged to ensure uninterrupted air flow.
• (iii) Oven may be pre-heated for materials with poor heat conductivity.
• (iv) The temperature is allowed to fall to 40°C, prior to removal of sterilized

14. o Precautions- Glass materials must be wrapped with clean
cloth or filter papers and should not be placed at the floor of
the oven as it receives direct heat.
o Advantages- It is used for sterilisation of oily & powders
materials and suitable for equipment's such as glass-wares,
syringes.
o Disadvantages- It is not suitable for plastic, rubber goods
because those materials exposed to a very high temperature
for a long time.
• This method is not suitable for surgical dressings.

15. • Moist heat may be used in three forms to acts by coagulation
and denaturation of proteins and to achieve microbial
inactivation.
• At temperature below 100°C. e.g. Pasteurization.
• At temperature 100°C. e.g. Boiling.
• At temperature above 100°C. e.g. Autoclave.
Autoclaving-
• It works on the principle of Steam Under Pressure and used
to generate high temperature needed for sterilization.
• The use of steam in the range of 121-134°C Temprature.

16. • Two type of cylinder are used. They are Horizontal
Autoclaves and Vertical Autoclaves. The combination of
Different Temprature and atmospheric pressure are used
for destroy the micro- organism and sterilize the material.
o For Autoclaving, Different Sterilization Conditions
Are:
Sr. No. Temprature
(in Degree
Celsius)
Time Required
(in min.)
Pressure
(lbs/sq.inch)
1 100 ℃ 90 0
2 110 ℃ 60 5
3 116 ℃ 30-40 10
4 121 ℃ 15-20 15
5 126 ℃ 10 20
6 135 ℃ 3 30

17. o Operation-
• Ensure that there should be sufficient water in the autoclave to
produce the steam.
• When water started boils, atmospheric pressure also increases, but if
pressure is raised, the temperature at which the water boils also
increases.
• The steam pressure starts raising & it comes to the desired pressure
i.e. 15 lbs/sq.inch with corresponding temperature 121°C and it will
take 15-20 minute. Allow to cool to about 40℃ before opening the
vent.
• The stages of operation of autoclaves include air removal, steam
admission and sterilization cycle includes:
• heating up,
• holding/exposure, and

18. o Advantages- It is used for sterilisation of surgical
dressings & surgical instruments. & It has more
penetrative power than dry air.
o Disadvantages- Drenching and wetting or articles may
occur, not suitable for powders & oils., takes long time to
cool.
Fig. Vertical Autoclave Fig. Horizontal Autoclave

19. • The major target of Radiations sterilization is microbial DNA.
• Two types of radiation are used:-
I. Ionizing. e.g. X-rays, Gamma.
II. Non-Ionizing. e.g. Infra-red, Ultraviolet.
o Ionizing rays (Cold sterilization) are high-energy rays with good penetrative
power.
• It employed to sterilize articles like syringes, glass- wares, fabrics gloves,
dressing packs, foods and pharmaceuticals.
o Non-ionizing rays (Hot sterilization) are low energy rays with poor
penetrative power. It control closed environment with UV lamp.
• It employed to disinfect hospital wards, operation theatres, virus laboratories,
corridors.

20. • Filtration process does not destroy but removes the micro-organisms. It is used
for both the clarification and sterilization of liquids and gases.
• It used to remove particles from solutions that can't be autoclaved and used to
remove microbes from heat labile liquids such as serum, antibiotic solutions,
sugar solutions etc.
o Different types of filters are:
1) Earthenware filters
2) Asbestos filters
3) Sintered glass filters
4) Membrane filters (for sterility testing)
o Air Filters: Air can be filtered using HEPA (High Efficiency Particle Air) filters. It is
usually used in biological safety cabinets.
o HEPA filters are at least 99.97% efficient for removing particles >0.3 μm in

21. o Chemical agents (disinfectant) are two types:
I. Liquid
i. Alcohol (Ethyl alcohol, Isopropyl alcohol, Tri-chlorobutanol)
ii. Halogen (Iodine, Chlorine)
II. Gases
• Ethylene Oxide
• Formaldehyde
Alcohol
o Mode of action: Alcohols dehydrate cells, disrupt membranes
and cause coagulation of protein/ involved in denaturation of
bacterial proteins.
• Alcohols are mainly used as sanitizing agent (disinfecting +
antiseptic) agent and an efficient at optimum conditions.

22. Halogen
o Mode of action: They are oxidizing agents and cause
damage by oxidation of essential enzymes.
• Examples: Chlorine compounds (chlorine, bleach,
hypochlorite) and iodine compounds (tincture iodine).
Gaseous Sterilization
• Gaseous sterilization involves the process of exposing
equipment or devices to different gases in a closed
heated or pressurized chamber.
• The most common gases used for sterilization include
ethylene oxide, ozone, nitrogen and chlorine dioxides.
• The chemically reactive gases ethylene oxide and
formaldehyde posses broad spectrum biocidal activity.

23. o R. M. Mehta, A textbook of “Pharmaceutics-1”, Sixth
Edition Reprint 2018, Vallabh Prakashan, Page No.
224-252.
o www.google.com
• https://www.researchgate.net/publication/3158044
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• www.microrao.com ‘Sterilization and Disinfection’.
o www.slideshare.com
• Mr. R.R. Patil, Sterilisation.
• Ch.Vamsi Anil Krishna, Sterilization.