Q-274. Evaluation of Methyl Bromide Fumigation for Decontaminating Bacillus anthracis Spore-Inoculated Indoor Surfaces

W. R. Richter1, M. Q. Shaw2, J. V. Rogers1, H. J. Stone1, S. P. Ryan3;
1Battelle Mem. Inst., Columbus, OH, 2Mem. Inst., Columbus, OH, 3US EPA, Research Triangle Park, NC.

Bacillus anthracis inhalation caused the deaths of five people in the United States in 2001, resulting in costly clean-up efforts. The potential for subsequent releases of B. anthracis spores is regarded as a plausible scenario for a terrorist attack. Since 2002, the U.S. Environmental Protection Agency’s (EPA) National Homeland Security Research Center (NHSRC) has been performing evaluations of technologies intended to decontaminate biological agents from indoor building surfaces. This study assessed laboratory-scale decontamination efficacy of methyl bromide (MeBr) fumigation against B. anthracis Ames spores deposited onto porous and non-porous indoor surface materials at various time points. Bacillus anthracis spores (1x107 to 1x108 CFU) were dried onto glass and ceiling tile and exposed to MeBr gas (80, 160, or 320 mg/L) for 3 to 24 hours. Relative humidity (40 ± 5% & 75 ± 5%) and temperature (37 ± 2°C) were maintained in the MeBr exposure and parallel positive control chambers for the duration of each test. Following MeBr exposure, viable B. anthracis spores were extracted, serially diluted, and spread onto semi-solid growth medium. MeBr exposure times ranging from 3 to 24 hours resulted in the log reduction of viable spores ranging from 0.1 to 6.9 and 0.2 to 7.1 on glass and ceiling tile, respectively. Biological indicators (containing Bacillus atrophaeus spores at 1 x 106 CFU), evaluated in parallel as a qualitative decontamination assessment, were not inactivated by MeBr exposure. These results show that MeBr gas can inactivate B. anthracis spores to a level of 6 logs or higher on indoor surface materials, providing kinetic kill curves for MeBr gas at three concentrations under controlled environmental conditions.