The response of Campylobacter jejuni to low temperature differs from that of Escherichia coli

Abstract

Human infection with Campylobacter jejuni is often associated with the consumption of foods that have been exposed to both chilling and high temperatures. Despite the public health importance of this pathogen, little is known about the effects of cold exposure on its ability to survive a subsequent heat challenge. This work examined the effect of rapid exposure to chilling, as would occur in poultry processing, on the heat resistance at 56 degrees C of two C. jejuni strains, 11168 and 2097e48, and of Escherichia coli K-12. Unlike E. coli K-12, whose cold-exposed cells showed increased sensitivity to 56 degrees C, such exposure had only a marginal effect on subsequent heat resistance in C. jejuni. This may be explained by the finding that during rapid chilling, unlike E. coli cells, C. jejuni cells are unable to alter their fatty acid composition and do not adapt to cold exposure. However, their unaltered fatty acid composition is more suited to survival when cells are exposed to high temperatures. This hypothesis is supported by the fact that in C. jejuni, the ratio of unsaturated to saturated fatty acids was not significantly different after cold exposure, but it was in E. coli. The low-temperature response of C. jejuni is very different from that of other food-borne pathogens, and this may contribute to its tolerance to further heat stresses.

FIG. 1.

Effect of exposure to 6°C on the shape of the death curve for C. jejuni 2097e48 at 56°C. Weibull analysis was performed on triplicate biological replicates for the resulting death curves of C. jejuni 2097e48 at 56°C, before and after exposure to 6°C. Open circles represent controls (37°C), and closed circles represent cells exposed to 6°C before heat treatment. Death values were analyzed using ANOVA at each time point. P values of <0.05 were considered significantly different; no significant differences were seen at any time points.

FIG. 2.

Effect of exposure to 6°C on the shape of the death curve for C. jejuni 11168 at 56°C. Weibull analysis was performed on triplicate biological replicates for the resulting death curves of C. jejuni 11168 at 56°C, before and after exposure to 6°C. Open circles represent controls (37°C), and closed circles represent cells exposed to 6°C before heat treatment. Mean values resulting from Weibull analysis of death curves are shown, with standard deviations given as error bars. Death values were analyzed using ANOVA at each time point. P values of <0.05 were considered significantly different and are shown on the figure as follows: *, P < 0.05; **, P < 0.01; and ***, P < 0.001.

FIG. 3.

Effect of exposure to 6°C on the shape of the death curve for E. coli at 56°C. Weibull analysis was performed on triplicate biological replicates for the resulting death curves of E. coli K-12 at 56°C, before and after exposure to 6°C. Open circles represent controls (37°C), and closed circles represent cells exposed to 6°C before heat treatment. Mean values resulting from Weibull analysis of death curves are shown, with standard deviations given as error bars. Death values were analyzed using ANOVA at each time point. P values of <0.05 were considered significantly different and are shown on the figure as follows: *, P < 0.05; **, P < 0.01; and ***, P < 0.001.