Most-probable-number rapid viability PCR method to detect viable spores of Bacillus anthracis in swab samples

A comparison of Most-Probable-Number Rapid Viability (MPN RV) PCR and traditional culture methods for the quantification of Bacillus anthracis Sterne spores in macrofoam swabs from a multi-center validation study was performed. The purpose of the study was to compare environmental swab processing methods for recovery, detection, and quantification of viable B. anthracis spores from surfaces. Results show that spore numbers provided by the MPN RV-PCR method were typically within 1-log of the values from a plate count method for all three levels of spores tested (3.1x10(4), 400, and 40 spores sampled from surfaces with swabs) even in the presence of debris. The MPN method tended to overestimate the expected result, especially at lower spore levels. Blind negative samples were correctly identified using both methods showing a lack of cross contamination. In addition to detecting low levels of spores in environmental conditions, the MPN RV-PCR method is specific, and compatible with automated high-throughput sample processing and analysis protocols, enhancing its utility for characterization and clearance following a biothreat agent release.