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 gastro‐intestinal 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.

Campylobacter jejuniBiofilms Up-Regulated in the Absence of the Stringent Response Utilize a Calcofluor White-Reactive Polysaccharide

“…Finally, our observations suggest that biofilm formation and the production of the CFW-reactive polysaccharide may represent important C. jejuni stress responses induced under adverse conditions such as those encountered during extended growth and in the absence of an SR. For instance, although C. jejuni stationary phase is typically associated with detrimental or poorly understood effects such as oxidative stress, peptidoglycan and metabolism changes, and conversion to coccoid and viable-but-nonculturable forms (31,74,75), it has recently been shown to elicit general increases and alterations in polysaccharide composition (18,52), similar to observations for other bacteria (9,14,43). Our stress response hypothesis is also consistent with the dim13 mutant serum sensitivity defect, the dim10 mutant late-stage culturability defect (which may reflect rapid nutrient depletion and toxic metabolite production without concomitant up-regulation of the protective polysaccharide), and a recent study describing the altered expression of oxidative and stress response proteins in biofilm versus planktonic populations of C. jejuni 11168 (36).…”

The Selective Value of Bacterial Shape

“…Similarly, in exponential phase Campylobacter jejuni grows as spiral cells that elongate into straight filaments, which are four times as long in late stationary phase (107,327). The latter forms coexist with residual coccoid cells (107,119,187,233,327). Whether this elongation phenomenon is more prevalent in spiral and vibrioid bacteria remains to be seen.…”

“…C. jejuni adopts variable forms: spirals, S shapes, commas, doughnut shapes, and dimpled cells (233). However, a "highly contentious" (327) disagreement exists over whether these shapes represent transitional or differentiated forms arising in response to environmental stress (107) or whether they are merely "old, inactive and degenerate" forms on their way to cell death (119,187,233,327). Needless to say, their participation in virulence is under debate.…”

Double-Staining Method for Differentiation of Morphological Changes and Membrane Integrity of Campylobacter coli Cells

“…The involvement of membrane blebs and budding in the process of coccoid formation in the absence of de novo protein synthesis and without changes in membrane protein composition indicates that the process is passive and potentially degenerative (15). There is evidence that the formation of coccoid C. jejuni cells is not an active process but represents a degeneration resulting from oxidative damage (5). After 72 h, C. coli cells showed coccoid forms.…”