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PRIS > Sterilisation and disinfection > Flashcards

Sterilisation and disinfection Flashcards

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1
Q

Why do we sterilise and disinfect?

A
  • Microorganisms in the environment
  • Host microbiome – want to avoid opportunist infection
  • Prevent spoiling of foodstuffs
  • Maintaining clean wounds to encourage proper repair process
  • Prevent infection!
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2
Q

Infection can be introduced into an organism or a system through several routes - what are these?

A
  • systemic
  • oral
  • local
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3
Q

How can infection enter systemically?

A
  • medicine and surgery
  • instruments, dressings, injectables
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4
Q

How can infection enter orally?

A
  • consumption of foodstuffs or medicines
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5
Q

How can infection enter locally?

A
  • application of products such as droplets or inhalers or suppositories
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6
Q

What is sterilisation?

A
  • the killing of ALL forms of microorganisms – including spores
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7
Q

What is disinfection?

A
  • elimination or reduction of vegetative microorganisms – excluding spores
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8
Q

What are two important things in sterilisation and disinfection?

A
  • important to prevent infection
  • preserve the characteristic of the item being sterilised or disinfected
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9
Q

What are the physical methods of sterilisation?

A
  • heat
  • radiation
  • filtration
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10
Q

What two types of heat can be used to sterilise?

A
  • dry heat = red, flaming, incineration, hot air oven
  • moist heat = temp below, above and at 100’C
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11
Q

What two types of radiation can be used to sterilise?

A
  • non ionising = infrared, ultraviolet
  • ionising = x-ray and gamma rays
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12
Q

What different methods of filtration can be used for filtration?

A
  • depth filter
  • membrane filter
  • air filter
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13
Q

What are the types of chemical sterilisation?

A
  • gaseous sterilisation
  • liquid sterilisation
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14
Q

What chemicals are used in gaseous sterilisation?

A
  • ethylene oxide
  • formaldehyde
  • nitrogen dioxide
  • ozone
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15
Q

What chemicals are used in liquid sterilisation?

A
  • hydrogen peroxide
  • glutaraldehyde
  • hypochlorite
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16
Q

Wet heat can be used for sterilisation - what are the 3 types of autoclave can be used?

A
  • bench top autoclaves
  • pressure autoclave
  • wall mounted autoclave
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17
Q

Before putting equipment in an autoclave what should be done?

A
  • equipment should be washed and disinfected to reduce parasitic burden
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18
Q

How does an autoclave function?

A
  1. steam enters the chamber jacket, passing through an operating valve
  2. enters the rear of the chamber behind a baffle plate.
  3. It flows forward and down through the chamber and the load exiting at the front bottom
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19
Q

How is jacket and chamber pressure of an autoclave maintained and what is the minimum pressure?

A
  • a pressure regulator
  • at a minimum of 15psi = the pressure required for the steam to reach 121’C
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20
Q

How is overpressure protection in autoclaves provided?

A
  • by a safety valve
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21
Q

In an autoclave what is the minimum time for pressure to be maintained?

A
  • 15-30 mins
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22
Q

How does a pressure cooker style autoclave work?

A
  • has a heating element and water level
  • held under pressure
  • heater heats up water and creates steam
  • don’t require external water supply making it easier and more accessible and takes up less space
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23
Q

What equipment could you not put in an autoclave?

A
  • sealed equipment such as containers as tram cant reach all of it to sterilise and they will collapse under pressure
  • plastics would melt
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24
Q

How can you monitor an autoclaves performance biologically?

A
  • use of spore forming microorganisms such as bacillus subtilis (requires culture)
  • biological indicator put in with load which changes colour to indicate load has failed
  • used monthly
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25
Q

How can you physically monitor an autoclave?

A
  • the time, temperature, pressure
  • sensors = temp. and pressure
  • probes - every time
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26
Q

How can you chemically monitor an autoclave?

A
  • autoclave tape or brown tubes
  • tapes go inside bag and turn black good indicator but cant tell you how long temp has been at that temperature
  • needs to be used in combination
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27
Q

What happens if something tightly wrapped is put in an autoclave?

A
  • steam may not be allowed to penetrate
28
Q

load pre-infection must be considered why?

A
  • as clean items or media may only require temperatures if 121’C for 15 minutes
  • waste may require 134’C for 30 minutes
29
Q

Why must packing of load in autoclaves need to be considered?

A
  • there needs to be enough space to allow for steam penetration
30
Q

Why must moisture be considered in autoclaves?

A
  • dry air prevents sterilisation at autoclave temperature
31
Q

Why must time be considered when using an autoclave?

A
  • there is a minimum time depending on load pre-infection
  • the higher the infection the longer the time required
32
Q

Why must temperature be considered when using an autoclave?

A
  • there is a minimum temperature to create penetrating steam
  • the higher the load pre-infection = the higher the temp required
33
Q

What can tape tell us about an autoclave?

A
  • tells us stream has reached the back, front, sides and middle
34
Q

What are dry heat ovens used for?

A
  • used for LPS (endotoxins) and some spores
35
Q

How do hot air ovens work?

A
  • Dry heat: at least 160oC for at least two hours, air is generally hotter to allow items to reach desired temperature; some people also use flames for sterilising items.
  • Used for depyrogenation (killing of endotoxin, also known as LPS) at temperatures of around 250’C ±15’C
36
Q

How can oven performance be monitored?

A
  • Biological – Use of spore-forming microorganisms such as Bacillus subtilis (requires culture)
  • Physical – time, temperature and pressure
    Sensors – temperature & pressure
  • Indicator tape – specific for dry heat ovens
37
Q

What are other heat methods (non-sterilisation)?

A
  • boiling 100’C
  • pasteurisation
38
Q

What does boiling at 100’C do?

A
  • endospores not killed (still useful for decontamination, it depends on the circumstances)
39
Q

What is pasteurisation?

A
  • Slow - 63-66°C x 30 minutes
  • Rapid - 73°C x 15 seconds in series
  • Kills M. bovis and B. abortus and many other zoonotic pathogens
40
Q

What radiation can be used for sterilisation?

A
  • UV irradiation
  • electron beam
  • x-rays
  • gamma irradiation = cobalt 60 = caesium 137
41
Q

How does UV irradiation work?

A
  • usually provided by UV lamps, used for surface disinfection, very effective for large areas, has poor penetration
42
Q

How does an electron beam work?

A
  • produced by electron beam accelerators, avoids the use of radioactivity and it is kinder to materials such as polymers. Reduced penetration compared to γ-irradiation
43
Q

How does x-ray work?

A
  • similar to electron beam, relatively new
44
Q

How does gamma irradiation work?

A
  • usually provided by 60Co source but also 137Cs used, deep penetration but can modify certain materials such as polymers, used for sterilization of bones, and other materials in surgery, also large scale sterilization of plastics
45
Q

What is membrane filtration?
What can the pores range from?
Why is it usually used?

A
  • Polymer films/membranes with microscopic pores
  • can range from 0.1 μm, 0.22 μm, 0.45 μm, etc – 0.22
  • usually used as most bacteria wont pass through this – viruses can though as they are smaller
46
Q

What size filter pore is required to screen out Yeats?

A

= 0.45 - 1.2 um

47
Q

What size filter pore is required to screen out bacteria?

A

= 0.2 um

48
Q

What size pore is required to screen pout viruses and mycoplasmas?

A

= 0.01 - 0.1
- expensive

49
Q

When do we use filters?

A
  • Filters are used for heat sensitive products, most are hydrophobic, for small volumes (laboratory) and large volumes (industrial purposes, example = filtered milk)
50
Q

What are disadvantages to using filters?

A
  • Some disadvantages such as saturation (clogging) and product retention, especially important when used for small quantities
51
Q

When are depth filters used?

A
  • Clarifying bulk products
  • Reducing bio-burden and filtering viruses (nanofiltration)
  • Reducing endotoxin (positively charged filters, similar to chromatography)
52
Q

Filtration alone is not considered sufficient when sterilisation by other means in the final container is possible.
If product cannot be sterilised in the final container, solutions or liquids can be filtered: How?

A
  • Through a filter of nominal pore size of 0.22 micron or less
  • Into a previously sterilised container
53
Q

Such filters can remove most bacteria and moulds but not what?

A
  • all viruses or mycoplasmas
54
Q

What consideration should be given to complementing the filtration process?

A
  • complementing the filtration process with some degree of heat treatment
55
Q

If it is not possible to use heat (terminal sterilisation) it is recommended to use what?

A
  • a second filtration
56
Q

Formalin can be used to chemically sterilise - what is it and what is it used for? and what should be considered?

A
  • 10% solution (made from stock solution at 43%)
  • used for fixing tissues, requires minimum contact time to ensure penetration of the solution into the tissue
    – thickness of tissue is an important consideration – works by crosslinking proteins
57
Q

What other chemicals can be used to sterilise?

A
  • Glutaraldehyde
  • 70% ethanol
  • acetone
58
Q

How can the use of chemicals be validated and what needs to be determined?

A
  • The ability of these chemicals to sterilise a sample/surface/material has to be properly validated against the microorganism of interest
  • minimum contact time needs to be determined
59
Q

Ethylene oxide gas (ETO can be used for chemical sterilisation - what percentages could this be used at?

A
  • CH2.O.CH2 - could be used as 100% or 12/88 (8.5% ETO and 91.5% CO2)
60
Q

When is ethylene oxide gas used?

A
  • Industrial sterilization for items that cannot be sterilised by irradiation or moist heat, such a polymers
  • Approximately 50% of medical devices in the USA are sterilised with ETO
61
Q

Why is ethylene oxide gas dangerous?

A
  • is carcinogenic, teratogenic, mutagenic and can induce spontaneous abortion, is volatile and explosive
62
Q

How is ETO believed to work?

A
  • its believed to work by alkylation of protein and DNA
63
Q

When is disinfection used?

A
  • Cleansing a wound or a room (surface/object)
  • Removal of dirt and potentially infectious organisms from an area/object
64
Q

Antiseptics have to be sufficiently stringent why?

A
  • to clean dirt and kill microorganisms but non-toxic to tissues
65
Q

What needs to be considered in both sterilisation and disinfectant?

A
  • dose
  • contact time
  • i.e. the amount and time of the agent/method applied to ensure microorganisms are inactivated or killed

PRIS (16 decks)

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