Flashcards in PA20024 Albert Bolhius Stuff! Deck (34)
What is the only steam suitable for autoclaving (moist heat sterilisation?)
Dry saturated steam!
This sits on the phase boundary between superheated steam (too dry, not enough moisture) and supersaturated steam (too wet, not hot enough)
What is latent heat?
When this heats exchanged it results in a change in physical state, no temperature change occurs, you cant see any temperature change eg converting from liquid to gas releases a lot of latent heat, known as super latent heat.
Latent heat can penetrate the surface of bacteria therefore is required to be released in moist heat sterilisation, that's why we use dry saturated steam as this is the only steam that releases this (as well as sensible heat)
What is sensible heat?
When this heat is exchanged, a change in temperature occurs. Ie heating up a liquid so that it's more likely to turn into a gas involves sensible heat. You can see the temperature increase.
Why is moist heat sterilisation better than dry heat sterilisation?
Moist heat uses dry saturated steam, which penetrates and damages bacteria using its latent heat and by hydration, it's a more rapid heat transfer and therefore takes less time.
Dry heat sterilisation does not use steam, involves oxidation which is less effective at inactivating bacterial spores than hydrolysis, and it is much slower heat transfer, you have to heat for a lot longer.
How much latent heat must be released in order to have enough energy transfer to kill bacteria?
946 BTU/lb latent heat
At 121 degrees, 15 PSIG, steam contains about 5 X more latent heat than sensible heat. What is so important about latent heat?
When the dry saturated steam comes into contact with the bacteria that is cooler, it will condense on the surface of the bacteria and release later heat into it which penetrates it, letting in more and more steam, a vacuum is then created which kills the bacteria.
Why is condensation of steam good for killing bacteria?
When the steam condenses there's more contact with the steam and microbe surface.
Steam gets sucked into the microbe through PORINS, more penetration.
You only get condensation with dry saturated steam
What type of sterilisation involves the use of autoclaving?
Moist heat sterilisation
In dry heat sterilisation, inactivation of microbes is principally by _____. In moist heat sterilisation, inactivation of microbes is principally by_______.
Dry heat: oxidation. Think: no water, only hot air, air=O2
Moist heat: hydrolysis. Think: water involved; OH, hydrolysis
What does the BP suggest as temperature and time for dry heat sterilisation?
160 degrees for 1 hour
(normally 150-180 degrees for 30 mins- 2 hours)
What's better about fan assisted ovens?
Temperature variation is under a lot More control than in a non fan assisted oven
What are the two gases used for gas sterilisation?
Formaldehyde (low temperature steam formaldehyde: LTSF)
What do you need to watch out for when using ethylene oxide gas to sterilise?
It's explosive if used over 3.6% concentration in the presence of AIR
Therefore we need to minimise the amount of air, ethylene oxide must be used in vacuum conditions, a special oven that sucks out all air.
Ethylene oxide is also toxic, and can leach out of products after sterilisation
Why do you need to control humidity when using ethylene oxide?
If organisms are in their dried out state then they're more resistant, therefore humidity needs to be controlled so it doesn't get too dry, humidity should be 30-70%, this is critical
What are the set amounts, temp and time for sterilisation by ethylene oxide?
900mg/L at 54 degrees for 3 hours
Or 450mg/L at 30 degrees for 16 hours
What are the set amounts, and temp for sterilisation by LTSF (formaldehyde)?
15-100mg/L at 70-75 degrees
(requires higher temps than ethylene oxide which can be used at room temps)
LTSF also has a longer cycle time than ethylene oxide
What do gamma ray sterilisers use as their radioactive source?
This needs to be used in a reinforced concrete building, and it should be stored under water when not in use, very radioactive.
What's the dose specified by the BP for radiation use to sterilise?
When using radiation as the sterilisation process, what will the units of your D value be in?
It will be a Dose of radiation, so usually kGy
What is radiation used to sterilise?
If you are we're using filtration with high temperature, which type of filter would you use?
This has thermal stability
What is breakthrough when applied to the process of filtration?
The number of bacteria after filtration, ie the number of bacteria that have managed to sneakily squeeze through the filter pores some how.
Larger pore size, higher bio burden, and large volume of filtrate all increase the likelihood of breakthrough occurring!
What is growthrough with regards to filtration?
This is when bacteria start to divide and grow through the filter membrane if a filtrate is left in contact with a membrane for too long.
To stop this occurring, minimise the time of the filtration process... The EP limits it to 4 hours.
What's the only practical way to sterilise liquids?
You can't use heat, radiation or gases
Could potentially use high intensity light (UV light) if transparent
How do we test air for contamination?
Use settle plates and air samplers
How do we test surfaces for contamination ?
Use contact plates and swabbing
When manufacturing batches in industry, why are you always going to have to make a few more than the number you're intending to sell?!
Because sterility tests need to be done on a fraction of the batch, and any product tested can't be used anymore, as sampling itself can introduce contamination. Eg if your batch is 100-500, 10 of these need to be sampled.
What are examples physical indicators, used for quality assurance of sterilisation processes?
Digital recording of temperature in coolest region in heat sterilisation process
Leak tests and pressure testing with gas sterilisation
Filtration: use bubble point pressure test (looking for the pressure required to push air through the filter)
What is an example of chemical indicators used for sterilisation quality assurance?
Change of colour observed such as brownes tubes, indicator strips, autoclave/Bowie dick tape.
Brownes tubes turn from red to green if autoclaving has worked and the high temp was reached.