Q-271. The Susceptibility of Bacillus atrophaeus Spores to Chemical Inactivation Is Dependent upon the Method of Spore Preparation

C. A. Zapka1, A. S. Yandell2, D. R. Macinga1;
1GOJO Industries, Inc., Akron, OH, 2Washington Univ., St. Louis, MO.

Background: Bacterial endospores are known to be extremely resistant to environmental and chemical stresses. Previous studies have demonstrated that the conditions under which spores are prepared can influence their resistance. A variety of spore preparation methods have been used in published studies investigating the efficacy of sporicidal disinfectant products. The purpose of this study was to determine whether the method used to prepare spores affects their observed resistance to sporicidal disinfecting agents. Methods: A time-kill suspension method was used to determine the sporicidal activity of various concentrations of bleach (NaOCl) against Bacillus atrophaeus spores. Efficacy testing was conducted using spores from either a commercial source or that were generated in the lab and exposed to differing conditions including heat-shock, alcohol-shock, triclosan treatment, or a combination or succession of these. Results: Spores from a commercial source were inactivated in 3 min by approximately 5000 ppm NaOCl. Lab prepared spores that were heat-shocked were more resistant and required >10,000 ppm NaOCl to achieve a similar inactivation. Both the alcohol and triclosan treated spores were more susceptible to NaOCl, requiring <1000 ppm NaOCl to observe similar inactivation. Surprisingly, the sensitivity of spores to bleach inactivation could be reversibly modified and was dependent upon the final treatment. For example when alcohol-treated spores were re-tested after a heat-shock treatment they became less susceptible and required approximately 10,000 ppm NaOCl for inactivation. Conclusion: The observed sporicidal efficacy of bleach against spores of Bacillus atrophaeus was dependent upon the conditions used to prepare the spore inoculum. A ten-fold greater concentration of bleach was required to achieve high efficacy against heat-shocked spores compared to alcohol-shocked spores. It is therefore important to consider the procedure used to prepare and store spores when interpreting sporicidal efficacy test results.