Studies were conducted into the formation and physiological state of coccoid cells of a strain of the human and animal pathogen Campylobacter jejuni. It was found that growth phase and the presence of chloramphenicol did not affect the rate of shape transformation from spiral to coccoid, while nutrient limitation, aeration of the medium and the presence of free-radical scavengers had profound effects. Coccoid cells were found to reduce the tetrazolium salts INT (2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride) and CTC (5-cyano-2,3-ditolyl tetrazolium chloride) to their respective formazans and this was linked to cellular respiration. However, respiring coccoid cells could not sustain their existence in prolonged adverse conditions, and it was concluded that they represent a degenerative stage rather than a dormant state of the organism.

Campylobacter jejuni cells, when stressed by aeration of the liquid culture medium, were protected from death when a block of wood was present in the broth, especially at 30 degrees C. Sealing the wood inside a porous membrane showed that access to its physical structure was necessary for the protection of cells and that soluble free-radical scavengers from the wood were not responsible for the protection seen. Insoluble free-radical scavengers associated with the wood were not a significant factor since other porous materials offered protection when their pores were sufficiently small (around 16 micron); and the wood itself needed to be at least 4 mm thick for the effect to be evident. Deeply scored plastic blocks did not enhance the survival of cells in aerated broths. Scanning electron microscopy was used to determine the size of the openings within the wood in relation to the size of the bacterial cells. Thus it was established that the physical structure of the wood, rather than its chemistry, was responsible for its protective effect. The consequences of this findings for the use of wooden cutting boards in food handling are discussed.