INTERPRETATION OF NONLOGARITHMIC SURVIVOR CURVES OF HEATED BACTERIA

SUMMARY— Complex survivor curves of heated bacteria are interpreted to be composites of several convex survivor curves that represent populations of different heat resistances in a single culture of bacteria. The variation in heat resistance appears to be physiological rather than genetic since subcultures of heat-resistant cells were no more heat resistant than the parent culture. Composite cures can appear to be nearly exponential. Results support a multiple-site hypothesis of thermal death. Tailing of survivor curves, with small numbers of cells surviving extended heating, was frequently noted when curves were carried through 6–9 log cycles. Such tailing might be of practical importance because it would predict that small numbers of cells might survive much longer heating than would be predicted from D-values calculated from curves carried through 4–5 log cycles.

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