Campylobacter jejuni is a microaerophilic pathogen but is able to survive oxidative stress conditions during its transmission to the human host. Strains of different origins (reference, poultry, or human clinical) were tested for survival under oxidative stress conditions. C. jejuni strains were grown in Mueller Hinton broth to obtain late exponential-phase cultures. Then they were exposed to 2 different stresses: (1) cultures were either plated on Columbia agar plates and exposed to atmospheric oxygen or (2) paraquat (a chemical oxidizing agent) was added to liquid cultures to reach a 500-microM concentration. Both of these experimental conditions were realized at 3 different temperatures: 4 degrees C, 25 degrees C, and 42 degrees C. Results obtained with paraquat and atmospheric oxygen were similar. Surprisingly, C. jejuni was found to be very sensitive to oxidative stress at 42 degrees C, which is its optimal growth temperature, whereas it was more resistant at 4 degrees C. A strain effect was observed, but no relationship was found between the origin of the strains and level of resistance. High temperature (42 degrees C) combined with oxidative stress allowed a rapid decrease in the C. jejuni population, whereas low temperature considerably decreased the effect of oxidative stress.

Aims:  To investigate potential resuscitation of Listeria monocytogenes and Salmonella Typhimurium after high hydrostatic pressure treatments. Methods and Results:  Pressure treatments were applied at room temperature for 10 min on bacterial suspensions in buffers at pH 7 and 5·6. Total bacterial inactivation (8 log10 CFU ml−1 of bacterial reduction) obtained by conventional plating was achieved regarding both micro‐organisms. Treatments at 400 MPa in pH 5·6 and 600 MPa in pH 7 for L. monocytogenes and at 350 MPa in pH 5·6 and 400 MPa in pH 7 for S. Typhimurium were required respectively. A ‘direct viable count’ method detected some viable cells in the apparently totally inactivated population. Resuscitation was observed for the two micro‐organisms during storage (at 4 and 20°C) after almost all treatments. In the S. Typhimurium population, 600 MPa, 10 min, was considered as the treatment achieving total destruction because no resuscitation was observed under these storage conditions. Conclusions:  We suggest a delay before performing counts in treated samples in order to avoid the under‐evaluation of surviving cells. Significance and Impact of the Study:  The resuscitation of pathogen bacteria after physical treatments like high hydrostatic pressure has to be considered from the food safety point of view. Further studies should be performed in food products to study this resuscitation phenomenon.

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Campylobacter jejuni represents one of the leading causes of bacterial enteritis throughout the world. Poultry is an important source of C. jejuni. Despite hygiene measures taken in the production chain, C. jejuni is frequently isolated from poultry meat. C. jejuni is a microaerophilic pathogen, affected by oxidative stress. Freeze-thaw treatment induces cell death by several mechanisms, including oxidative stress. In this article, we investigate the role of oxidative stress in C. jejuni sensitivity during and after a freeze-thaw treatment. This treatment results in dead and sublethally injured cells. The latter population might have an increased sensitivity to oxidative stress. To test this, cells were stored for another 24 h at 4 degrees C under aerobic conditions and compared to cells that were not treated. C. jejuni survival was measured in different media (water, BHI broth, chicken juice, and chicken fillets) to test the environment protective effect. Different strains were tested, including sodB (encoding the superoxide dismutase) and cj1371 (encoding a periplasmic protein) mutants. Cell death was particularly important in water but similar in BHI, chicken juice, and chicken fillets. The sodB mutant was more sensitive to freeze-thaw treatment, suggesting that the killing mechanism involves production of superoxide anions. On the contrary, the cj1371 mutant was more sensitive to storage at 4 degrees C, suggesting that it does not play a role in the detoxification of reactive oxygen species. Storage at 4 degrees C after freeze-thaw treatment increases cell death of oxidative stress-sensitive populations. Sensitization to oxidative stress, freeze-thaw treatment, and further storage at 4 degrees C could be a way to reduce C. jejuni populations on carcasses.

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