Bacteria possess certain characteristics such as: some require oxygen to live, they are known as Aerobic. Those that do not are know as Anaerobic. There are bacteria that are called Thermostabile, which means that they are not easily altered or decomposed by heat… those that are Thermolabile are easily decomposed by heat.
You will also come across the term spore. A spore is a reproductive cell produced by plants and some protozoans - it is the asexual reproduction of many unicellular animals and plants. These spores possess thick walls enabling them to withstand unfavorable environmental conditions such as extreme heat.
Certain bacteria form spores but more in the nature of a defense mechanism than for reproduction. These spores are difficult to destroy because they are very resistant and require prolonged exposure to heat to destroy them.
So, as we see, some bacteria love heat, and if they are spore formers, high heat alone will not do the job, so dry heat is out.
Some sterilizers utilize boiling water and steam in an unsealed receptacle know as “flowing steam”… temperature 212° F (IOO C)… this is also inadequate. Boiling water alone is good for tea and coffee but useless against bacteria.
Exposing the article to heat and steam at intermittent intervals, called tyndal-ization… is another inadequate procedure.
How about sterilization by gas, e.g., ethylene oxide. Great, but too explosive. Or formaldehyde… again, great, but formaldehyde is trapped in a ruling right now linking it as a carcinogen (able to cause cancer); also too dangerous.
We are narrowed down to the autoclave, the instrument of choice, that kills not only bacteria, but also spores.
To autoclave properly, we must first understand the mechanics of the system. This employs a temperature of 273° F, with steam under pressure of 15-17 pounds per square inch (PSI) for 30 minutes (50 minutes from cold start) and a 15 minute cool down or drying period (the door can be open about 1″ during this period).

Posted on August 20th, 2008 by admin
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Filed under: Sterile Techniques