Identification of a novel stress resistance mechanism in Campylobacter jejuni

Aim: To study stress resistance mechanisms in Campylobacter spp. Methods and Results: Campylobacter strains were grown to the appropriate phase in Brucella broth. The cells were diluted into either cell‐free spent medium (obtained by filtration of a grown culture) or a freshly prepared medium and the pH reduced to 4·5, a lethal pH value. At suitable time intervals survivors were enumerated on Campylobacter blood free selective agar base. The cell‐free spent medium from mid‐exponential and stationary phase had a protective effect on acid and thermal stress in Campylobacter jejuni CI 120, a natural isolate. The protective effect of the extracellular compound was not significantly inactivated by boiling, but was inactivated by proteinase. Conclusions: The present study suggests that a protein (or proteins) accumulated by C. jejuni CI 120 during growth may play an active role in the induction of stress responses and that this protein is heat stable. Significance and Impact of the Study: The results indicate that C. jejuni CI 120, a natural isolate, has the ability to use extracellular signalling mechanisms to induce tolerance to stress factors. This is a major advancement in the understanding of the physiological basis for survival of C. jejuni in the environment.