Comparative proteomic analysis of Listeria monocytogenes tolerance to bile stress

The ability of the food-borne pathogen Listeria monocytogenes to tolerate bile is critical to its successful infection and colonization in the human gastrointestinal tract. Using comparative proteomics, a total of 48 proteins were identified in this study in the presence of moderate (0.3 %) or high (3 %) level of bile salts in the wild-type strain EGD. Identified proteins fell into 14 functional categories covering most of the biochemical functions of bacterial cells, indicating that there were complex physiological mechanisms involved in L. monocytogenes tolerance of bile stress. Among them, 16, 14, and 18 proteins were expressed differently in the isogenic deletion mutants of L. monocytogenes EGDΔsigB, EGDΔprfA, and EGDΔprfAΔsigB, respectively, compared with their parent strain EGD at corresponding concentrations of bile salts. All proteins identified in EGDΔsigB and EGDΔprfAΔsigB were all down-expressed in the presence of bile salts, whereas several proteins were up-expressed in EGDΔprfA, in particular at the high level of bile (3 %), indicating that SigB plays an essential positive role in L. monocytogenes tolerance of bile stress and that the negative effect of PrfA may facilitate its survival in bile in the gastrointestinal tract before its successful colonization and invasion.