Other sterilisation processes

Question 1

How does dry heat inactivate things?

Answer 1

Oxidation

Question 2

How does moist heat inactivate things?

Answer 2

Hydrolysis

Question 3

What are the uses of Dry heat sterilisation?

Answer 3

Substances that can’t be subjected to moisture
Materials not penetrable by steam (oils, fats, waxes)
Glassware
Metal surgical instruments

Question 4

What are the disadvantages of Dry heat sterilisation?

Answer 4

May take a long time to heat up
Temperature must be higher and for longer than moist heat (160C, 1 hour)
Some objects may oxidise at high temp
Large temp variations can be found within a load (if no fan)

Question 5

What are the uses of Gas sterilisation?

Answer 5

Temperature sensitive materials (e.g plastics, devices with electronics)

Question 6

What are the advantages of Gas sterilisation?

Answer 6

Good alternative for heat/radiation sensitive materials

Some products work at room temp

Question 7

What are the disadvantages of Gas sterilisation?

Answer 7

Slow (not usable if high throughput)
Toxic (requires more complex equiptment, safe usage)
Gas may be absorbed (addition of more gas during process)

Question 8

What are the two gases used in gas sterilisation?

Answer 8

Ethylene oxide and Formaldehyde

Question 9

What are the advantages of Ethylene oxide?

Answer 9

Broad spectrum, non-selective
Bactericidal
Can act at room temp
Low incidence of product deterioration

Question 10

What are the disadvantages of Ethylene oxide?

Answer 10

Expensive
Toxic
Need to store products in a safe area after sterilisation while the gas leaches out
Can be explosive

Question 11

What are the advantages of Formaldehyde?

Answer 11

Broad spectrum, non-selective
Bactericidal
Not flammable or explosive

Question 12

What are the disadvantages of Formaldehyde?

Answer 12

Toxic
Low penetration power
Slow acting
May leave residue of polymers (block pipes)
Leaching of gas afterwards needs to occur

Question 13

What is the most commonly used type of radiation for sterilisation?

Answer 13

Gamma rays.

Goes in order ‘GEXU’

Question 14

What is the main target of radiation sterilisation?

Answer 14

DNA

Question 15

How does radiation cause damage?

Answer 15

Direct: Ionisation
Indirect: Radiolysis of water

Question 16

What are the uses of radiation for sterilisation?

Answer 16

Disposable plastics
Decontaminate raw materials
Radiation-stable ointments

Question 17

What are the main features of Filtration?

Answer 17

Cold process (good for heat-sensitive products)
Fast
Aseptic process (special operation needed)
Not absolute (breakthrough and grow through)

Question 18

What are the mechanisms of filtration?

Answer 18

Sieving (screen filter)
Adsorption
Trapping in filter matrix (depth filter)

Question 19

What are the two types of filter?

Answer 19

Screen filter (absolute, low holding capacity)

Depth filter (not absolute, high holding capacity)

Question 20

Dead-end filtration is…

Answer 20

Fast but ‘filter-cake’ build up

Question 21

Crossflow filtration is…

Answer 21

Slower ‘than dead-end’ but self-cleaning

Question 22

What is breakthrough? (In relation to filtration)

Answer 22

Depth filters are not absolute and have a capacity limit

This means that some microbes/particles may pass through the filter

Question 23

What factors does breakthrough depend on?

Answer 23

Size/conc of contaminant
Volume
Flow rate

Question 24

What are the solutions to breakthrough?

Answer 24

Start with a low bioburden or use filters in a series

Question 25

What is growthrough? (in relation to filtration)

Answer 25

If left in contact with a membrane filter for a long time, bacteria will divide and grow through the filter

Question 26

What is a solution to growthrough?

Answer 26

Limit the time of the filtration (i.e less than 4hrs)