The document outlines various physical methods of sterilization that eliminate microorganisms through processes like drying, dry heat, moist heat, filtration, and radiation. Key techniques include drying, flaming, incineration, pasteurization, boiling, autoclaving, and different filtration methods, each effective under specific conditions for different materials. Additionally, the document discusses the use of non-ionizing and ionizing radiation for sterilization, highlighting their mechanisms and applications.

1. PHYSICAL METHOD OF
STERILIZATION
SWETHA. S
BP231507
I M.SC., MICROBIOLOGY

2. STERILIZATION
• Sterilization is the process of killing of microorganisms.
• It refers to the process that removes, kills or deactivates all forms of life and other biological agents
present in or on a specific surface, object or fluid.
• It was carried out by two methods.
1) Physical method
2) Chemical method

3. 1) PHYSICAL METHOD OF STERILIZATION
(a) DRYING
* Moisture is essential for the growth of bacteria. Four – fifth of the weight of the bacterial cell is
due to bacteria.
* Drying in has a deleterious effect on many bacteria.
* Spores are unaffected by drying.

4. (b) DRY HEAT
i) Flaming
* In Flaming, inoculation loops, tips of forceps and spatulas are held in a Bunsen burner flame till they
become red hot.
Sterilization of Inoculation loop by Flaming

5. ii) Incineration
* Incineration is an excellent method for safely destroying materials such as contaminated cloth,
animal carcasses and pathological materials.
* The equipment used for the Incineration process is Incinerator.
Laboratory Incinerator

6. iii) Hot air oven
* Sterilization by Hot air oven is the most widely used method for sterilization by Dry heat.
* Hot air oven is used to sterilize glasswares, forceps, scissors, scalpels, glass syringes and swabs.
* “Temperature required for sterilization is inversely proportional to Time” is the principle of Hot air
oven.
* During the sterilization of materials in Hot air oven, the sterilization time was reduced when the
sterilization temperature was increased.
* Temperature and duration for Hot air oven sterilization is
▪ 140 °C for 11/2 hours
▪ 160 °C for 1 hours
▪ 180 °C for 1/2 hours
* Sterilization by Hot air oven kills the microorganisms by denaturation of proteins.

7. (c) MOIST HEAT
i) Pasteurization
* Pasteurization is the fractional sterilization process of milk.
* Pasteurization technique was introduced by Louis Pasteur.
* During Pasteurization, all the spore forming bacteria and heat resistant bacteria were killed.
* Pasteurization was carried out by two methods.
1. Holder method (63 °C for 30 minutes)
2. Flash method (72 °C for 15 - 20 seconds)
Milk Pasteurization Plant in Industries

8. ii) Boiling
* Vegetative bacteria are killed almost immediately at 90 – 100 °C, but spore forming bacteria required
prolonged period of boiling.
* Boiling is not recommended for the sterilization of instruments.
* Boiling is usually preferred for cooking the food materials.
Boiling of Water

9. iii) Tyndallization
* Tyndallization is a process dating from the nineteenth century for sterilizing substances, usually
food, named after its inventor, scientist John Tyndall.
* It is still occasionally used.
* Tyndallization can be used to destroy the spores.
* Tyndallization essentially consists of heating the substance to boiling point (or just a little below
boiling point) and holding it there for 15 minutes, three days in succession.

10. iv) Autoclave
* An autoclave is a pressure chamber used to carry out the sterilization under pressure (Moist heat).
* The mechanism of the autoclave is similar to the pressure cooker.
* Autoclave works under the principal of Boyl’s Law – “When volume is constant, temperature is
directly proportional to time”.
* Temperature and duration for Autoclave sterilization is 121 °C or 15 lbs for 20 minutes.
* Sterilization by autoclaving kills the microorganisms by coagulation of proteins.
Autoclave

11. (d) FILTRATION
* Filtration helps to remove the bacteria from heat liable substances such as serum, sugar solutions or
antibiotics used for the preparation of culture medium.
* Four types of filtrations are commonly used for the sterilization process. They are
i. Candle filters
ii. Asbestos filters
iii. Sintered glass filters
iv. Membrane filters

12. i) Candle filters
* Candle filters are manufactured in different grades of porosity.
* They have been widely used widely for the purification of water for drinking and industrial process.
* They are of two types:
1. Unglazed ceramic filters (e.g) Chamberland filter and Doulton filter
2. Diatomaceous earth filters (e.g.) Berkefeld filter and Mandler filter
ii) Asbestos filter
* Asbestos filters are disposable, single – use discs.
* They have high absorbing capacity and tend to alkalinize filtered liquids.
* Examples of Asbestos filter include Seitz filters and Sterimat filters.

13. iii) Sintered glass filter
* Sintered filters are prepared by heat fusing finely powdered glass particles of graded size.
* They have low absorptive property and can be cleaned easily but are brittle and expensive.
iv) Membrane filters
* Membrane filters are made up of cellulose esters or other polymers have largely replaced other types
of filters.
* Membrane filters are routinely used in water purification and analysis, sterilization and sterility
testing and for preparation of solutions for parental use.

14. (e) RADIATION
* Two types of radiations are used for sterilization. They are
a) Non – ionizing radiation
b) Ionizing radiation
i) Non – ionizing radiation
* Infra red and Ultraviolet rays are the non – ionizing low energy type.
* Infra red radiation is used for rapid mass sterilization of prepacked items such as syringes and
catheters.
* Ultraviolet radiation is used for disinfecting enclosed areas such as entry ways, operation theaters and
laboratories.

15. ii) Ionizing radiation
* X – rays, Gamma rays and Cosmic rays are high energy ionizing type.
* Ionizing radiations are lethal to DNA and other vital constituents.
* They have high penetrative power.
* Ionizing radiations are used to sterilize plastics, swabs, catheters, animal feeds, cardboards, oils,
greases, fabrics and metal foils.

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