Evaluating the efficacy of disinfecting products against Bacillus subtilis spore using an optimized method

Abstract

Twenty disinfectant products were evaluated for sporicidal activity using an optimized method. Bacillus subtilis ATCC 6051 was sporulated in Difco sporulation medium for 3 days. The spores were purified using density centrifugation and heat treatment and then prepared for sporicidal efficacy assessment. The quality of the purified spores was verified using sodium hypochlorite solutions with free chlorine concentrations of 1,500 ppm and 5,000 ppm. The active ingredients in disinfectant products included chlorine, hydrogen peroxide/peracetic acid, aldehydes, quaternary ammonium compounds, and phenols. Of the 20 products tested, six met the effectiveness criterion of greater than a 5 log₁₀ reduction after exposure of B. subtilis spores for the label-recommended contact time. Among the 11 products claiming sporicidal activity, four met the established criterion. Among the five categories of active ingredients evaluated, some chlorine-based and hydrogen peroxide/peracetic acid-based products demonstrated significantly higher sporicidal activity than products in the other three categories. Overall, products that did not meet the study criteria exhibited less than a 1 log₁₀ reduction. When these underperforming sporicidal products were tested with an extended contact time of 10 minutes, one additional product met the effectiveness criterion. Subsequent quality assessments using freshly prepared, laboratory-made products containing identical active ingredients demonstrated improved sporicidal efficacy compared with the original test items, indicating that defects or degradation of active ingredients may have occurred in some of the tested commercial disinfectant products.