Mechanisms behind tailing in the pressure inactivation curve of a clinical isolate of Escherichia coli O157:H7

The tailing in pressure inactivation curve of clinically isolated Escherichia coli O157:H7 was investigated. A typical tailing was observed after the treatment period for 30 min when 10(7) CFU/ml of the cell suspension was subjected to pressure treatment at 300 MPa and 25 degrees C. There was no effect on the tailing profiles by the addition of pressure-killed cells and released cellular components. When cells survived at a tail portion were repropagated (tail-culture) and subjected to second pressure treatment, the cells of the tail-culture exhibited eminently higher barotolerance compared to those of the original-culture, suggesting that the presence of genetically pressure-resistant subpopulation was responsible for the tailing. The cytoplasmic membrane of the tail-culture cells had higher stability to a pressure treatment at 100MPa for 10min than that of the original-culture, which was evidenced by lower permeability to ethidium bromide. The addition of non-ionic surfactants including 0.5 wl/ml polyoxyethylene p-t-octylphenyl ester (Triton X-100) and 0.53 mg/ml lauric sugar ester dramatically reduced the level of tailing and made the inactivation curve linear. (c) 2006 Elsevier B.V. All rights reserved.