Sporicidal effect of disinfectants on Bacillus cereus isolated from the milk processing environment

The sporicidal efficacy of sodium hypochlorite and a combination of peracetic acid and hydrogen peroxide on Bacillus cereus spores isolated from the milk processing environment was examined using the European Suspension Test and by a surface disinfection test on stainless steel and rubber. The results of the laboratory tests were compared with field trials in a milking installation. In general, it was difficult to obtain consistent results, as the repeatability and reproducibility of the tests were found to vary according to the test strain, spore suspension preparation, disinfectant test solution, organic load, contact time and temperature. The sporulation medium used to obtain spores influenced the sporicidal effect considerably. To overcome this problem a standard method for preparation of spore suspensions should be prescribed. The various disinfectants were more effective in suspensions than on surfaces and in field trials. For the suspension tests SE values ranging from 1.0 to 3.0 were reached within 10 min at 50°C, depending on the disinfectant used. Sodium hypochlorite-based products were most effective. The activity on spores on surfaces and in field trials was limited. In surface tests reductions of 0.4–0.8 were observed within 10 min at 50°C depending on the type of surface. The SE values obtained for rubber were lower compared with stainless steel. The decrease in spore levels found in the milking installation was comparable with the surface experiments, i.e. 0.4–1.0. It is important to develop standard test procedures to assess the sporicidal efficacy of disinfectants used in food hygiene. Surface tests should be included to reflect the in-use conditions more closely and minimum standards should be determined for both suspension tests and surface tests.