Other sterilisation processes Flashcards
How does dry heat inactivate things?
Oxidation
How does moist heat inactivate things?
Hydrolysis
What are the uses of Dry heat sterilisation?
Substances that can’t be subjected to moisture
Materials not penetrable by steam (oils, fats, waxes)
Glassware
Metal surgical instruments
What are the disadvantages of Dry heat sterilisation?
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)
What are the uses of Gas sterilisation?
Temperature sensitive materials (e.g plastics, devices with electronics)
What are the advantages of Gas sterilisation?
Good alternative for heat/radiation sensitive materials
Some products work at room temp
What are the disadvantages of Gas sterilisation?
Slow (not usable if high throughput)
Toxic (requires more complex equiptment, safe usage)
Gas may be absorbed (addition of more gas during process)
What are the two gases used in gas sterilisation?
Ethylene oxide and Formaldehyde
What are the advantages of Ethylene oxide?
Broad spectrum, non-selective
Bactericidal
Can act at room temp
Low incidence of product deterioration
What are the disadvantages of Ethylene oxide?
Expensive
Toxic
Need to store products in a safe area after sterilisation while the gas leaches out
Can be explosive
What are the advantages of Formaldehyde?
Broad spectrum, non-selective
Bactericidal
Not flammable or explosive
What are the disadvantages of Formaldehyde?
Toxic
Low penetration power
Slow acting
May leave residue of polymers (block pipes)
Leaching of gas afterwards needs to occur
What is the most commonly used type of radiation for sterilisation?
Gamma rays.
Goes in order ‘GEXU’
What is the main target of radiation sterilisation?
DNA
How does radiation cause damage?
Direct: Ionisation
Indirect: Radiolysis of water
What are the uses of radiation for sterilisation?
Disposable plastics
Decontaminate raw materials
Radiation-stable ointments
What are the main features of Filtration?
Cold process (good for heat-sensitive products) Fast Aseptic process (special operation needed) Not absolute (breakthrough and grow through)
What are the mechanisms of filtration?
Sieving (screen filter)
Adsorption
Trapping in filter matrix (depth filter)
What are the two types of filter?
Screen filter (absolute, low holding capacity)
Depth filter (not absolute, high holding capacity)
Dead-end filtration is…
Fast but ‘filter-cake’ build up
Crossflow filtration is…
Slower ‘than dead-end’ but self-cleaning
What is breakthrough? (In relation to filtration)
Depth filters are not absolute and have a capacity limit
This means that some microbes/particles may pass through the filter
What factors does breakthrough depend on?
Size/conc of contaminant
Volume
Flow rate
What are the solutions to breakthrough?
Start with a low bioburden or use filters in a series
What is growthrough? (in relation to filtration)
If left in contact with a membrane filter for a long time, bacteria will divide and grow through the filter
What is a solution to growthrough?
Limit the time of the filtration (i.e less than 4hrs)
