Define Sterilization : 

Definition : Sterilization is the killing or removal of all microorganisms including bacterial spores which are highly resistant.

Method of sterilization:

Physical methods :

A) Heat:

1. Dry heat:

• Red heat
• Flaming
• Hot air oven
• Incineration

2. Moist heat :

At 100° C

• Boiling
• Steming
• Tyndalization

Above 100° C

• Autoclave

Below 100° C

• Pasteurization
• Vaccine bath
• Water bath
• Inspissator

B) Radiation:

• X-rays
• u-rays

C) Filtration :

• Berkefeld type
• Chamberland type.
• Seitz type.
• Membrane filters.

Chemical methods :

1. Phenol
2. Cresol
3. Dettol
4. Acids & alkalis
5. Halogens
6. Formaldehyde
7. Gluteraldehyde
8. Detergents.

Importance of sterilization:

1. To prevent infection to the patient.
2. To prevent nosocomial infection.
3. To prevent infection to the doctors and medical staffs.
4. To prevent infection to the microbiologists and medical students.

How post-operative infection can be prevented by sterilization :

1. Unnecessary drainage should be avoided.
2. Isolation of septic patients.
3. Isolation of patients prone to infection.
4. Non touch technique of stitch removal.
5. Dressing with sterile technique.
6. Prophylactic antibiotic if needed.

Define autoclave :

Definition :  Autoclave is a method of sterilization by moist heat in which substance are sterilized at 121° C for 15 minutes.

Principle of autoclave :

1. At atmospheric pressure, water boils at 100° C.
2. With the rise of pressure, the boiling point of water also rises.
3. Steam under pressure unmixed with air has more temperature than that mixed with air.
4. Steam under pressure has more penetrating power. This is due to fact that steam condenses water on contact with materials.
5. During condensation of steam to water, a large amount of latent heat is liberated, thus increasing the efficacy of sterilization.

Autoclave Mechanism of action:

1. Materials are kept inside.
2. Close the lid
3. Set the safety valve at the desired pressure.
4. Heat the autoclave. Air is forced out and eventually steam ensures out through the tap.
5. Close the tap
6. Then temparature 121°C is obtained by giving desired pressure.
7. Keep it for 15 minutes.
8. Stop heating
9. Cool the autoclave
10. Open the stopcock slowly to allow air to enter the autoclave.

Checking of autoclave:

1. Spores of bacillus stearothermophilus if killed the function of autoclave is proper.
2. Automatic monitoring system.