Sterility Testing

Testing of sterility is an important quality control procedure. Autoclaves have pressure gauges and thermometers that monitor the sterilization operation. These monitors are supplemented with internal monitors. Chemicals that darken when exposed to specific heat treatments are sometimes included with each sterilization batch. These chemicals are often impregnated into a tape or wrapping material so that, after adequate exposure to elevated temperature, the darkened chemical spells out the word STERILE or AUTOCLAVED (see Figure). In this way the proper operation of the sterilizer is monitored and, simultaneously, the sterilized material is properly labelled.

Another method for monitoring the operation of the sterilizer is to use a biological indicator. This is the best method for assuring adequacy of the sterilization procedure because the method actually monitors the death of heat-resistant endospores. Typically, spores of Bacillus stearothermophilus are used for monitoring the effectiveness of steam sterilizers. The indicator consists of a strip of filter paper impregnated with B. stearo­thermophilus spores. The test strip is exposed to the sterilization procedure and viability is tested by placing the strip in a nutrient solution. After incubation for 24 hours the tube containing the spore strip and nutrient solution is examined for growth. The lack of growth indicates successful sterilization; the occurrence of any growth indicates a failure of the sterilization system.

Photograph showing sterility check with special heat-sensitive tape. Left flask is before sterilization and right flask is after au-toclaving. The heat sterilization causes the letters on the tape to appear, indicating that the media has been autoclaved.

Дата добавления: 2015-08-05