Sterilisation

Question 1

Define Sterilisation and Disinfection

Answer 1

Sterilisation: removal of all viable micro-organisms inlcuding bacterial and fungal spores.

Disinfection: removal or killing of disease causing microorgansism; does not remove spores.

Question 2

The difference between bactericidal and bacteriostatic?

Answer 2

Bactercidal- kills bacteria

Bacteriostatic - inhibits growth of bacteria

Question 3

What is the difference between Antiseptic and Asepsis?

Answer 3

Antiseptic - substance used on/or in living tissue for inhibiting or destroying micro-organisms.

Asepsis - prevention of access of micro-organsisms to materials.

Question 4

What are the types of dry heat sterilisation?

Answer 4

a) Hot air oven —Temp. 160C –180C for 1 hour - main means of dry heat sterilisation.

b) Flaming— direct exposure for a few seconds in a gas or spirit flame

c) Red heat—holding inoculating wires, forceps and spatulas until red hot

d) lncineration— total destruction by burning

e) Infra-Red Radiation— Infra-Red rays are directed from an electrically heated element onto the objects to be sterilized.
* >200C by Infra-Red radiation in vacuo is employed in sterilisation of surgical instruments.

Question 5

What are the types of moist heat sterilisation?

Answer 5

Moist heat sterilisation includes boiling, live steam and steam under pressure.
It is cheaper, quicker and more efficient.

1. Autoclaving:
   - Uses saturated steam under pressure
   - Sterilisation ensured at 121C for 15mins at 15lbs pressure.
   - Kills microorganisms including spores
   - Widely used to sterilise surgical supplies and bacteriological culture media.

Question 6

What are the autoclave controls (ways of ensuring that sterilisation is being done thoroughly)?

Answer 6

1. Tenperature record
2. Thermocouple
3. Indicators
   a) Chemical - sterilizing agent has penetrated package and has reached instrument. Do not guarantee sterilisation but helps detect procedural errors like overloaded steriliser and Incorrect packaging.
   Eg. Bowie Dick Autoclave Tape
   Browne’s Tubes (A small glass tube containing a red heat-sensitive dye. Dye changes to green after a defined period of time at a certain temperature but is not proof of sterilization).

b) Biological - spore strips eg. Bacillus stearothermophillus spores are hlghly resistant to heat and steam. If the autoclave can kill these tough spores, it can be assumed that all other microorganisms have been destroyed.

Question 7

What is the Pasteurisation method of disinfection?

Answer 7

• Ensures the destruction of non-spore forming organisms.
  Eg. Mycobacteria (mycobacteria bovis)/
  Coxiella burnetti may survive.

Two methods:
1. Holder method: Heating to 63C-66C for long duration (30mins), then rapidly cooling. Inactivates bacteria and viruses.

2. Flash method: Rapidly heating a liquid product to a specific temperature (72C) for a very short duration (20s), then quickly cooling it down. This process effectively destroys pathogenic microorganisms.

Question 8

The Boiling disinfection technique

Answer 8

Vegetative organisms killed at 100C for 10mins.
Does not ensure sterility.
Used for treatment of bowl and instruments for wards and theatres.