Abstract
Developing a quick and inexpensive method to extract bacteria from HVAC filters can provide valuable information on the extent of contamination of a building after a release of pathogenic microorganisms. In order to identify the preferred extraction procedure of Bacillus thuringiensis HD1011 from a pleated filter with a minimum efficiency reporting value of 7, different agitation methods were varied systematically. This study shows that the vortex–shake extraction procedure was found to be significantly more efficient when preceded by sonication; the vortex–shake sequence had a mean of 0.49 (0.3–0.77) CFUs (colony forming units) compared to 1.3 (0.8–2.1) CFUs for sonicate–vortex–shake agitation. The control data suggested that growth was occurring when the filter was present in the bacterial solution, and this was investigated further. The data with no filter ever present produced a mean of 0.37 (0.14–0.47) CFU compared to the means of 0.85 (0.52–1.35) CFU and 1.07 (0.65–1.74) CFUs, respectively, for when the filter was present for agitation and when it was present for 24 h prior to agitation, indicating significant growth. Because these results suggest that germination could occur during the extraction procedure, all the results were quantified based on presence versus absence using a most probable number method.
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