CmeR-dependent gene Cj0561c is induced more effectively by bile salts than the CmeABC efflux pump in both human and poultry Campylobacter jejuni strains
The multidrug efflux pump CmeABC described in the food-borne pathogen Campylobacter jejuni was shown to be an important element of bile resistance and significant for successful colonization of chicken intestines. Recently, another gene (Cj0561c) strongly suppressed by the same repressor (CmeR) that regulates expression of CmeABC was identified in C. jejuni NCTC 11168. Initial data suggested that, similarly to cmeABC, Cj0561c could be induced by bile salts. In the present study, the occurrence of the Cj0561c gene and bile-salt-dependent induction was investigated in ten poultry and eight human C. jejuni strains. The Cj0561c gene was present in all strains. When cultured without addition of bile salts, the transcription level of that gene was about tenfold higher than that of cmeABC. Bile salts cholate and taurocholate induced transcription of cmeABC 1.66-fold and 2.71-fold and that of Cj0561c 3.71-fold and 10.99-fold, respectively. Thus Cj0561c was more effectively induced by bile salts than cmeABC and taurocholate was superior to cholate as an inducer of transcription. More efficient induction of both cmeABC and Cj0561c by taurocholate might be the reason for the higher minimum inhibitory concentrations (MICs) observed with taurocholate than with cholate (100 mg/ml vs. 10 mg/ml). There was no significant difference between poultry and human C. jejuni strains concerning the transcription levels of cmeABC and Cj0561c in cultures without bile salts and concerning bile-salt-induced changes in transcription of cmeABC and Cj0561c. Thus, higher MIC values observed for taurocholate in human strains than in poultry strains (200 mg/ml vs. 75 mg/ml) could not be explained by different responses of cmeABC and Cj0561c to bile salts. Therefore, they must be due to another mechanism.
