Evaluation of Microbial Loads of Bacillus subtilis Spores on Penicylinders

Abstract

Three types of penicylinders were compared for their retention of spores of Bacillus subtilis testing for sporicidal activity of disinfectants. Glass, porcelain, and stainless steel penicylinders are inoculated with a water suspension of B. subtilis var. niger (ATCC 9372) spores and dried. One set of each type of penicylinder is submerged 1 h in 0.9% saline. One set of porcelain penicylinders is submerged 15 h in a neutralized chemical germicide, and one set is also inoculated with a culture filtrate of B. subtilis (ATCC 19659), dried according to the AOAC method, and submerged 1 h in 0.9% saline. Microbial loads simulate those held on carriers used to test sporicidal activity of disinfectants. Carriers are immersed in chemical germicide, transferred to a neutralizer, and placed in a culture medium. Average percentages of B. subtilis var. niger spores retained on 10 carriers after 1 h submersion in saline and in water were as follows: glass, 93.6%; porcelain, 99.9%; and stainless steel, 99.5%. Retention of spores after 15 h submersion in a neutralized chemical germicide and in water was 98.9%. Porcelain penicylinders inoculated from a culture filtrate of B. subtilis (ATCC 19659) retained 26% of the spores after being submerged 1 h in saline and placed in water. Glass penicylinders, which retained the lowest and most variable number of spores, were the least suitable for sporicidal activity testing. B. subtilis (ATCC 19659) spores tested on porcelain penicylinders met only the minimum HCl resistance requirements of > or = 2 min. On porcelain penicylinders, the resistance of B. subtilis var. niger spores to 2.5N HCl was relative to the number of spores inoculated.