Test method development to evaluate hot, humid air decontamination of materials contaminated with Bacillus anthracis ΔSterne and B. thuringiensis Al Hakam spores

To develop test methods and evaluate the survival of Bacillus anthracis Delta Sterne and Bacillus thuringiensis Al Hakam spores after exposure to hot, humid air. Spores (>7 logs) of both strains were dried on six different test materials. Response surface methodology was employed to identify the limits of spore survival at optimal test combinations of temperature (60, 68, 77 degree C), relative humidity (60, 75, 90%) and time (1, 4, 7 days). No spores survived the harshest test run (77 degree C, 90% r.h., 7 days), while > 6.5 logs of spores survived the mildest test run (60 degree C, 60% r.h., 1 day). Spores of both strains inoculated on nylon webbing and polypropylene had greater survival rates at 68 degree C, 75% r.h., 4 days than spores on other materials. Electron microscopy showed no obvious physical damage to spores using hot, humid air, which contrasted with pH-adjusted bleach decontamination. Test methods were developed to show that hot, humid air effectively inactivates B. anthracis Delta Sterne and B. thuringiensis Al Hakam spores with similar kinetics. Hot, humid air is a potential alternative to conventional chemical decontamination.