Analysis of coccal cell formation by Campylobacter jejuni using continuous culture techniques, and the importance of oxidative stress

Abstract

Campylobacter jejuni is an important human gastrointestinal pathogen. In hostile environments it may adapt its physiology to prolong survival, potentially including the adoption of a viable, non-culturable form and a change to coccal cell morphology. By independently controlling the individual parameters of continuous cultures of Camp. jejuni (e.g. pH, nutrient limitation, growth rate, etc.), coccal cell formation was shown to be elicited only by high oxygen tension in conjunction with reduced carbon concentration. Electron microscopy revealed degradative changes in these cells. This occurred as a transient response over 48 h coincident with a large reduction in maximum growth rate and viable count. Kinetic analysis of the biomass reduction of the cultures demonstrated that significant underlying growth was maintained, with the subsequent selection of a more oxygen-resistant population of cells and reversion to spiral morphology. Coccal cells appear to be predominantly a degenerate form of Camp. jejuni resulting from oxidative damage. While some of these coccal cells may recover, the more interesting population of cells is probably that which retains, or regains, spiral morphology during adaptation to oxidative stress.