Spore Testing

A standard procedure should be established for the routine evaluation of each sterilizer using biological indicators. This should be done at a minimum of once a week. Your personnel should put forth every effort toward the standardization of sterilizing techniques within the guidelines established by the equipment manufacturer. Frequent third party monitoring of the sterilization process by culture tests, the maintaining of exact standards for the preparation, packaging and loading of medical supplies in the sterilizers, plus intelligent and painstaking attention to details are recognized as essential to the effective sterilization of medical supplies.

Use of Biological Indicator Strips. When using paper spore strips inoculated with bacterial spores to determine the efficacy of sterilization processes, care should be taken to use biological indicators which meet published guidelines for the sterilant and temperature ranges being tested. It is also necessary to ensure proper placement of each strip in the portion of the test pack or load most inaccessible to the Steam, EtO, chemical, or dry heat sterilant. The recommended procedure is to select one or more of the largest and most dense packs which normally constitute a routine load of bulk supplies and insert the glassine envelope containing the inoculated strips in the center of each pack. Identify the test pack with an indelible marking instrument, and place the pack on the edge on the bottom shelf or the sterilizer chamber, near the front. Add the remainder of the load in a like manner without indicators, and operate the sterilizer according to the manufacturer's recommendations. Upon completion of the sterilizing cycle, remove the glassine containing the biological indicator from the test pack and deliver them along with an unexposed biological control, to the laboratory for sterility testing of the strips, i.e. Coastal BioTech Services, Inc..

Biological Indicator Culturing Procedures. We at Coastal BioTech Services, Inc. will complete the culturing procedures. All tests for sterility should be conducted by a microbiologist or clinical technician observing rigid aseptic techniques throughout the procedure. The glassine test envelope will be aseptically opened and the spore strip carefully transferred to a tube of sterile culture media or equivalent. Resistance values and outgrowth rates may vary depending on the source of the SCDB used for spore recovery. The spore strips need to be incubated for seven days at 30-35C for dry heat or gas-EO sterilizer testing and 55-60C for steam or chemiclave sterilizer testing.

Biological Indicator Interpretation. We at Coastal BioTech Services, Inc. will observe to tubes daily during the incubation cycle. The presence of turbidity and/or a color change to yellow indicates bacterial growth, presumably due to the spores having survived the sterilization process. According to USPXXII, a biological indicator spore strip following exposure to gas-EO, chemiclave, or steam at 121C is to have a specific survival and kill times which correspond to its D value and spore concentration. The survival time is when 100% of the exposed biological indicators demonstrate growth upon culturing in SCDB and the kill time results in no growth of all biological indicators exposed.

Biological Indicator Controls. At least one control should be included with each test series. This requires the transfer of an unexposed spore strip to a tube of sterile culture media, followed by incubation at the same temperature corresponding to the test strips. Microbiological growth indicates that the medium possesses suitable growth promoting properties and the spore strips contained viable spores prior to the sterilizing process. Conversely, a microbiological medium control consisting of one or two tubes of sterile culture media is also included in the incubation cycle. The absence of growth following incubation would indicate that the media was sterile prior to the sterility test procedures.

 

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