Effect of filtration of bacterial suspensions on the inactivation ratio inhydrostatic pressure treatment

The effects of filtration on the inactivation of vegetative cell suspension s (Escherichia coli and Salmonella typhimurium) and spore suspensions (Baci llus subtilis and Bacillus licheniformis) by hydrostatic pressure treatment were investigated. There was no significant difference in the inactivation ratios between the filtrated and unfiltrated vegetative cell suspensions. However, filtrated spore suspensions were inactivated more easily than the unfiltrated ones. B. subtilis spores filtrated were sterilized (6-log-cycle s) in a 90 min treatment, but the unfiltrated spores were inactivated 5-log -cycles in a 180 min treatment. B. licheniformis spores filtrated were inac tivated approximately 4-log-cycles, but the unfiltrated spores were inactiv ated approximately 3-log-cycles in a 180 min treatment. These results indic ated that the filtration of spore suspensions was effective to increase the inactivation ratio by the hydrostatic pressure treatment. However, filtrat ion did not contribute to increasing the inactivation ratio of vegetative c ell suspensions. (C) 2001 Elsevier Science Ltd. All rights reserved.