An investigation into the phenomenon of cross-protection in Escherichia coli O157:H7

Rowe, M.T.; Kirk, R.

An investigation into the phenomenon of cross-protection in Escherichia coli O157:H7

1999

Rowe, M.T. | Kirk, R.

Micro-organisms which are subjected to non-lethal stress can exhibit significantly greater resistance when both the same or an unrelated stress is subsequently reapplied. This latter phenomenon is termed 'cross-protection' and has been shown to be mediated, at least in part, by the rpoS gene. In experiments using three strains of Escherichia coli O157:H7 one strain showed a significantly greater resistance to salt (20% w/v) when prestressed at pH 4(.)5, 4(.)0 and 3(.)5 compared with the control (pH 7(.)0) using lactic acid as the acidulent. The two other strains only exhibited significantly greater resistance when prestressed at pH 4(.)5 and 4(.)0. Further work using only one strain showed that when prestressed at pH 4(.)0 (only pH value tested) it exhibited a significantly greater resistance when subsequently heated at 56 degrees C for up to 80 min. Using an acid/salt stress combination the cross-protection phenomenon was shown to be induced with initial adaptation times as short as 15 min (shortest time investigated). In an experiment with rpoS mutant of E. coli O157:H7 this gene was shown to be responsible for inducing most, but not all, of the cross-protection phenomenon. This work, particularly the speed of the adaptation process, indicates the need for fundamental studies of this phenomenon to enable more accurate risk assessment to be made of food process operations.

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