Molecular mechanisms of ' Campylobacter jejuni ' pathogenesis and survival in the environment

Campylobacter jejuni is the major foodborne gastrointestinal pathogen. The wide of use of antibiotics in medicine and in animal husbandry has resulted in increased incidence of antibiotic resistance in Campylobacter. In this study, C. jejuni G1 strain was found to be more resistant to tetracycline (Tet) when compared with the reference strain NCTC11168, despite the absence of the Tet resistance gene tet(O) in both strains. Comparative genomics analysis revealed a remarkable difference between the sequences of the cmeB genes in these strains. The inner membrane protein CmeB is a component of the CmeABC multidrug efflux pump. Mutation of gene cmeB in the G1 strain resulted in a 32-fold reduction of resistance to Tet and increased sensitivity to a number of other antibiotics, confirming the predicted role of CmeB. Transfer of the pTet plasmid from C. jejuni 81-176 to the G1 strain increased the level of Tet resistance above that of the former, suggesting that CmeB of strain G1 has a higher potency to excrete this drug than that of the orthologues in strains 81-176 and 11168. Preliminary experiments using Acanthamoeba polyphaga as a model organism also suggested a possible role of the CmeB protein in invasion of, and survival within these host cells, which may be important for bacterial protection in adverse environmental conditions. In addition, site-directed mutagenesis of a capsular polysaccharide-related gene kpsM led to decreased ability of strain 81-176 to invade A. polyphaga, suggesting a role of the capsule in this process.