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Background   Campylobacter jejuni  is a major cause of bacterial food-borne illness in Europe and North America. The mechanisms allowing survival in the environment and transmission to new hosts are not well understood. Environmental free-living protozoa may facilitate both processes. Pre-exposure to heat, starvation, oxidative or osmotic stresses encountered in the environment may affect the subsequent interaction of  C. jejuni  with free-living protozoa. To test this hypothesis, we examined the impact of environmental stress on expression of virulence-associated genes ( ciaB, dnaJ,  and  htrA ) of  C. jejuni  and on its uptake by and intracellular survival within  Acanthamoeba castellanii .    Results  Heat, starvation and osmotic stress reduced the survival of  C. jejuni  significantly, whereas oxidative stress had no effect. Quantitative RT-PCR experiments showed that the transcription of virulence genes was slightly up-regulated under heat and oxidative stresses but down-regulated under starvation and osmotic stresses, the  htrA  gene showing the largest down-regulation in response to osmotic stress. Pre-exposure of bacteria to low nutrient or osmotic stress reduced bacterial uptake by amoeba, but no effect of heat or oxidative stress was observed. Finally,  C. jejuni  rapidly lost viability within amoeba cells and pre-exposure to oxidative stress had no significant effect on intracellular survival. However, the numbers of intracellular bacteria recovered 5 h post-gentamicin treatment were lower with starved, heat treated or osmotically stressed bacteria than with control bacteria. Also, while ~1.5 × 10 3  colony forming unit/ml internalized bacteria could typically be recovered 24 h post-gentamicin treatment with control bacteria, no starved, heat treated or osmotically stressed bacteria could be recovered at this time point. Overall, pre-exposure of  C. jejuni  to environmental stresses did not promote intracellular survival in  A. castellanii .    Conclusions  Together, these findings suggest that the stress response in  C. jejuni  and its interaction with  A. castellanii  are complex and multifactorial, but that pre-exposure to various stresses does not prime  C. jejuni  for survival within  A. castellanii .

Effect of environmental stress factors on the uptake and survival of Campylobacter jejuni in Acanthamoeba castellanii