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In general, any instrument that enters an already sterile part of the body (such as the blood, or beneath the skin) should be sterilised. This includes things like scalpels, hypodermic needles and artificial pacemakers.
Heat sterilisation is known to have been in used in Ancient Rome, but it mostly disappeared throughout the Middle Ages where sanitation was not usually a concern.
The preferred principle for sterilisation is through heat. There are also some chemical methods capable of sterilisation.
Probably the most widely used method for heat sterilisation is the autoclave. Autoclaves commonly use steam heated to 121°C, at 103 kPa (15 psi), for 15 minutes. The steam and pressure allow sufficient heat is transferred into the organism to kill them.
Proper autoclave treatment will inactivate all fungi, bacteria, viruses and also bacterial spores, which can be quite resistant. It will not however necessarily eliminate all prions (discussed later).
To ensure the autoclaving process was able to cause sterilisation, most autoclaves haves meters and charts that record or display pertinent information such as temperature and pressure as a function of times. Indicator tape is often taped onto packages of products to be autoclaved. The tape contains a chemical that will change colour if the appropriate conditions have been met. Some types of packaging have built-in indicators on them. Biological indicators, (such as the Attest s), can also be used. These contain Bacillus sterothermophilus spores, which are amongst the toughest organisms an autoclave will have to destroy.
After a run in an autoclave, the internal glass in the Attest vial is shattered, allowing the spores into a differential liquid medium. If the autoclave destroyed the spores, the medium will remain a blue colour. If autoclaving was unsuccessful the B. sterothermophilus will metabolise, causing a yellow colour change after two days of incubation at 56°C.
For effective autoclaving, the steam needs to be able to penetrate everywhere. For this reason, an autoclave must not be overcrowded, and the lids of bottles and containers must be ajar. Indicators should be placed in the most difficult place sterilisation is wanted, for instance if you are sterilising the contents of universals (a universal is a type of small glass jar), the Attest vial should be placed in a universal, to ensure that steam actually penetrates these areas.
For autoclaving, as for all disinfection of sterilisation methods, the cleaning off of any biological material is also critical. Biological matter or any grime may shield organisms from the property intended to kill them, whether it physical or chemical. Cleaning can also remove a large number of organisms at once. Proper cleaning can be achieved by physical scrubbing to remove dirt; this should be done with detergent and warm water to get the best results. Where it is not feasible, ultrasound or pulsed air can be used to remove debris. Other heat methods include using dry heat, boiling, flaming and incineration.
Flaming is done to loops and straight-wires in microbiology labs. Leaving the loop in a Bunsen burner until it glows red, ensures that any infectious agent gets oxidised completely into small molecules. Heating small metal or glass objects is really the extent to which this method is used.
Incineration will also burn any organism to ash. It obviously is only used to sanitise unwanted medical and other waste before its ash goes to the tip. Boiling in water for 15 minutes is unsuitable for sterilisation. It’s a simple and familiar enough process for anyone to do, though is hazardous and cumbersome. Boiling will kill bacteria and viruses, but it is ineffective against many bacterial spore s and prions.
Dry heat can be used to sterilise items, but as the heat takes much longer to be transferred to the organism, both the time, and the temperature required, must be increased. The standard setting for a hot air oven is at least two hours at 160°C. A rapid method heats air to 190°C for 6-12 hours. Dry heat has the advantage that it can be used on powders and other heat-stable items that are adversely affected by steam. (E.g. it won’t cause rust.)
In terms of prion elimination there is no agreed ideal time and temperature. The prion that causes the disease scrapie (strain 263K) is inactivated relatively quickly by standard sterilisation procedures. Other strains of scrapie, as well as strains of CJDCJD can mean: Creutzfeldt-Jakob disease chronological Julian day TLAs. and BSEThe abbreviation BSE could stand for Bovine spongiform encephalopathy Bombay Stock Exchange TLAs. have shown much more resistance.
Using mice as a test animal, one experiment showed that heating BSE postive brainFor other articles about other subjects named brain see brain (disambiguation). In the anatomy of animals, the brain or encephalon is the supervisory center of the nervous system. Although the brain is usually cited as the supervisory center of vertebrate tissue at 134-138°C for 18 minutes resulted in only a 2.5 log decrease in prion infectivity. (The initial BSE concentration in the tissue was relatively low).
To have a significant margin of safety, cleaning should reduce infectively 4 logs, and the sterilisation method reduce it a further 5 logs. The recommendations state 121-132°C for 60 minutes, and 134°C for at least 18 minutes. There is little conclusive evidence to prove this is either sufficient or insufficient, though the BSE example above does not seem to suggest it's appropriate.
By combining immersion in sodium hydroxideSodium hydroxide ( Na OH), also known as caustic soda or lye in North America, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents. Sodium hydroxide is occasionally used in t (NaOH 0.09N) for two hours, with one hour autoclaving (121°C) several investigators have shown complete (>7.4 logs) inactivation. (Sodium hydroxide may, though, be deleterious to surgical instruments.)