Comparative evaluation of hydrogen peroxide sporicidal efficacy by different standard test methods

BACKGROUND AND OBJECTIVES: There are different sporicidal standard tests with various specifications to deal with products that are claimed for sporicidal activity. The aim of this study was to compare the 7% H(2)O(2) sporicidal efficacy against Bacillus subtilis spores using different standard test methods. MATERIALS AND METHODS: The 7% H(2)O(2) sporicidal efficacy against Bacillus subtilis spores was determined according to the AOAC MB-15-04 standard of carrier test and two standard suspension tests (BS EN 13704, AFNOR NF 72-230) in both clean and dirty conditions and by using different interfering substances including bovine serum albumin, yeast extract and skimmed milk. RESULTS: The results of suspension tests with 3 × 10(5) and 2 × 10(7) CFU/ml of B. subtilis spore concentration demonstrated that the higher spore counts lead to lower efficacy of 7% H(2)O(2). Also, the sporicidal activity of 7% H(2)O(2) was reduced in the presence of interfering substances. Bovine serum albumin, yeast, and skimmed milk showed similar interfering effects in suspension test with 3 × 10(5) CFU/ml. While, in suspension tests with higher initial spore count (2 × 10(7) CFU/ml) severity of interfering effects were intensified and distinct. Our results indicated that the carrier sporicidal test in comparison with suspension tests required more contact time to kill B. subtilis spores. CONCLUSION: The results of this study showed that it is reasonable to use interfering substances and inoculated carriers in accordance with actual conditions of product usage in a sporicidal test. Interfering substances may reduce the contact surface between H(2)O(2) and test spores; therefore, the sporicidal efficacy of H(2)O(2) was diminished. So applying suspension test in clean condition to verify the claim of sporicidal activity is strongly discouraged.