Physical Methods of Sterilisation

Question 1

Flaming

Answer 1

Inoculation loop or Wire, the tip of Forceps and spatulas are held in a bunsen flame till they are red hot.

Question 2

Incineration

Answer 2

This is an excellent method of destroying materials such as contaminated cloth, animal carcasses and pathological materials.

Question 3

Hot Air Oven (Sterilisation by Dry Heat)

Answer 3

Kills by oxidation effects.
The oven utilizes dry heat to sterilize articles .
Operated between 50oC to 250/300oC.
A holding period of 160oC for 1 hr is desirable.
There is a thermostat controlling the temperature.
Double walled insulation keeps the heat in and conserves energy.

Question 4

Hot Air Oven (uses)

Answer 4

To sterilise Forceps, Scissors, Scalpels, Swabs.

Pharmaceuticals products like Liquid paraffin, dusting powder, fats and grease.

Question 5

Moist heat sterilization

Answer 5

Kills microorganisms by coagulating their proteins

Question 6

Pasteurisation

Answer 6

Process of killing of pathogens in the milk but does not sterilize it .

Milk is heated at 63oC for 30 mins.
(HOLDER METHOD)

At 72oC for 15-20 Sec. Rapid cooling to 13oC
(FLASH PROCESS)

Question 7

Hot water bath

Answer 7

To inactivate non sporing bacteria for the preparation of vaccines - Special vaccine bath at 60oC for one hour is used

Serum or body fluids containing coagulable proteins can be sterilized by heating for 1 hr at 56oC in a water bath for several successive days.

Question 8

Inspissator

Answer 8

Sterilizes by heating at 80-85oC for half an hour for 3 successive days

Used to sterilize media such as Lowenstein-Jensen & Loefller’s serum

Question 9

Boiling (temperature at 100oC)

Answer 9

Kills vegetative forms of bacterial pathogens.
Hepatitis virus: Can survive up to 30 minutes of boiling.
Endospores: Can survive up to 20 hours or more of boiling

Question 10

Steam sterilizer (steam at atmospheric pressure)

Answer 10

Steam is generated using a steamer (Koch/ Arnold)
Consists of a Tin cabinet
Has a conical lid to enable the drainage of condensed steam
Perforated tray above ensures materials are surrounded by steam.
For routine sterilization exposure of 90 mins is used

For media containing sugar and gelatin exposure of 100oC for 20 min for 3 successive days is used
The process is termed as
Tyndallisation /Intermittent Sterilization

Question 11

Autoclave

Answer 11

Autoclave consists of a vertical or a horizontal cylinder.
One end has an opening which is meant for keeping materials to be sterilised.
The lid is provided with a Pressure gauge, to measure the pressure
A safety valve is present to permit the escape of steam from the chamber
Articles to be sterilised are placed in the basket provided
Sterilisation is carried out under pressure at 121º for 15 mnts.