title: Bile salts modulate expression of the CmeABC multidrug efflux pump in Campylobacter jejuni.
abstract: CmeABC, a multidrug efflux pump, is involved in the resistance of Campylobacter jejuni to a broad spectrum of antimicrobial agents and is essential for Campylobacter colonization in animal intestine by mediating bile resistance. Previously, we have shown that expression of this efflux pump is under the control of a transcriptional repressor named CmeR. Inactivation of CmeR or mutation in the cmeABC promoter (PcmeABC) region derepresses cmeABC, leading to overexpression of this efflux pump. However, it is unknown if the expression of cmeABC can be conditionally induced by the substrates it extrudes. In this study, we examined the expression of cmeABC in the presence of various antimicrobial compounds. Although the majority of the antimicrobials tested did not affect the expression of cmeABC, bile salts drastically elevated the expression of this efflux operon. The induction was observed with both conjugated and unconjugated bile salts and was in a dose- and time-dependent manner. Experiments using surface plasmon resonance demonstrated that bile salts inhibited the binding of CmeR to PcmeABC, suggesting that bile compounds are inducing ligands of CmeR. The interaction between bile salts and CmeR likely triggers conformational changes in CmeR, resulting in reduced binding affinity of CmeR to PcmeABC. Bile did not affect the transcription of cmeR, indicating that altered expression of cmeR is not a factor in bile-induced overexpression of cmeABC. In addition to the CmeR-dependent induction, some bile salts (e.g., taurocholate) also activated the expression of cmeABC by a CmeR-independent pathway. Consistent with the elevated production of CmeABC, the presence of bile salts in culture media resulted in increased resistance of Campylobacter to multiple antimicrobials. These findings reveal a new mechanism that modulates the expression of cmeABC and further support the notion that bile resistance is a natural function of CmeABC.
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, 1116 Veterinary Medicine Complex, Iowa State University, Ames, IA 50011, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Lin
authors.forename: Cédric
authors.initials: C
authors.lastname: Cagliero
authors.forename: Baoqing
authors.initials: B
authors.lastname: Guo
authors.forename: Yi-Wen
authors.initials: YW
authors.lastname: Barton
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Maurel
authors.forename: Sophie
authors.initials: S
authors.lastname: Payot
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001647:Bile Acids and Salts / Q000378:metabolism / Q000494:pharmacology*; D016123:Campylobacter jejuni / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008826:Microbial Sensitivity Tests; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000502:physiology*; D009876:Operon / Q000502:physiology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000378:metabolism; D020349:Surface Plasmon Resonance; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001647:Bile Acids and Salts; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012097:Repressor Proteins; D001616:beta-Galactosidase