S84: Testing strategy to assess decontamination of bacterial spores on surfaces

As a bacterial spore, Bacillus anthracis released as an aerosol for a biological attack could maintain viability while airborne and deposited on surfaces.  Due to the spore’s innate tolerance to disinfectants, decontamination of surface-bound spores at attacked sites would likely require advanced technologies for adequate pathogen kill.  Decontamination testing to evaluate disinfection treatments requires defined factors, including (1) spore physiological state, (2) exposure conditions (temperature and pH), (3) disinfectant concentration, demand, and neutralization, and (4) viability quantification to derive inactivation kinetics.  A great challenge to disinfectant testing of surface-bound spores is assessing spore viability.  Viability assessment typically involves (1) spore removal from surfaces following disinfectant exposure and (2) quantifying spore viability of removed spores by cultivation on growth medium.  Consequently, low viability counts could be attributed to spore inactivation as well as partial recovery of spores from surfaces.  To overcome spore recovery from surfaces as a confounding variable, a testing strategy was developed to employ both plate counts and direct microscopic counts to quantify spore inactivation on surfaces.  The system involves (1) exposing surface samples with attached spores to disinfectant, (2) eluting spores from surfaces by mixing with buffer, (3) concentrating and washing spore eluate by membrane filtration, and (4) enumerating viable spores by plate count and total spores by microscopic count (Petroff-Hausser chamber).  Plate-count to microscopic-count ratios provided accurate assessments of spore inactivation on various surfaces (textile fabric and porous and non-porous hard materials).  In addition, the system demonstrated significant impact of sample material on spore adhesion to surfaces.