Sterilisation & Disinfection

Question 1

Define sterilisation

Answer 1

The complete destruction of all living organisms from a surface, item or liquid

Question 2

Describe the different moist heat methods of sterilisation

Answer 2

• Autoclave: water is boiled under pressure of 15lb per square inch so boiling occurs at 120 degrees
• Boiling: endospores are not killed
• Tyndilisation: repeated steaming at 100 degrees on 3 consecutive days = time consuming

Question 3

Describe dry heat methods of sterilisation

Answer 3

Hot air oven or open flame

Question 4

Describe radiation methods of sterilisation

Answer 4

• UV destroys viruses, bacteria + DNA and used to decontaminate theatres
• alpha-radiation from cobalt-60 is used to sterilise heat liable materials = dangerous!!

Question 5

Describe the filtration method of decontamination (not quite sterilisation)

Answer 5

Used to remove bacteria from a solution (i.e. Liquids for injection)
Some viruses may pass through

Question 6

Describe chemical methods of sterilisation

Answer 6

• 10% formalin + water = formaldehyde
  V. Powerful oxidising agent and steriliser
• 10% Ethylene oxide gas
  Industrial sterilisation of plastic

Question 7

Describe the ways to test the effectiveness of an autoclave

Answer 7

• Autoclave tape: becomes stripy
  …however will change from kettle steam
• Browns tubes + indicator strips: change colour
  (Browns tubes from red –> green + indicator strips from yellow –> blue) when correct temperature is reached
  …still doesn’t tell us if microorganisms have been killed
• Bacillus stearothermophilus strips: added to grow medium, bacterial growth indicates the autoclave isn’t working

Question 8

What are antiseptics?

Answer 8

Disinfectants that are non-toxic enough to be applied to living tissue