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Greetings Neda Parya,
I would like to refer you back to questions Q00131, Q00119, Q00081, Q00047 and Q00027.
The most common method worldwide to test the effectiveness of steam sterilizers is the Biological Indicator Spore Test. This test uses bacterial spores that are harder to kill than regular bacteria, viruses, molds, and other micro-organisms. Bacillus stearothermophilus spores are the most common type of bacterial spore used to test steam sterilizers.
Commercial pre-made sterilizer biological test packs at reasonable prices are available from several different vendors. Some vendors are willing to offer free incubators if you buy thier brand of biological test. To make your own Challenge Biological test pack:
Begin with 16 freshly laundered, preconditioned, huck or 100% cotton surgical towels about 16 x 26 inches or 41 x 66 centimeters in size. Fold towel in thirds, and then in half.
Stack the towels with the folds opposite each other; pointing in opposite directions.
Place a biological indicator in the center of the pack. This indicator should have 1,000,000 b. stearothermophilus spores.
Place two bands of tape around the pack, making a pack about 6 inches or 15 centimeters high. Do not use a wrapper because this adds another variable when you want to reproduce the results later.
Place the pack flat on a rack with the layers of towels horizontal in the coldest spot in the sterilizer. This is typically at the front of the sterilizer chamber, directly over the drain.
Run the biological test with a routine full load at the regular routine sterilization cycle in the sterilizer. (This is different from the Bowie Dick style test used to check the air removal qualities of Hi Vacuum steam sterilizers. That test must be run in an empty sterilizer for a specific time.)
Each day that biological tests are run, a control test from the same lot that has not been sterilized must also be incubated. This control test demonstrates the pre-sterilization viability of the spores, that the growth media can grow organisms, and the incubation temperature is correct. The time it takes before you know the results of a biological test vary greatly depending on the manufacturer's method of indicating growth. Some take 7 days, others take 3 hours. I would recommend that you do not use biological test strips in glassine envelopes. Transferring the strip from the envelope to the media is a source of contamination and many false positive tests. Question 131 addressed the frequency of testing, but remember that this also relates to your recall policy. When a biological test shows growth after a sterilization cycle, you must repackage and resterilize everything processed in the sterilizer since the last good (no-growth) test. If you run a test one time a week, and it takes 3 days to get a result from the test, then a positive test means that you must reprocess everything run through the sterilizer for the last 10 days! If you have a busy department that keeps the sterilizers busy all day, this can be a major disaster.
Regards, Pete Bobb
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