CmeR Functions as a Transcriptional Repressor for the Multidrug Efflux Pump CmeABC in Campylobacter jejuni

Abstract

<p>CmeABC, a resistance-nodulation-division (RND) type of efflux pump, contributes to <em>Campylobacter</em> resistance to a broad spectrum of antimicrobial agents and is also essential for <em>Campylobacter</em> colonization of the animal intestinal tract by mediation of bile resistance. As one of the main systems for <em>Campylobacter</em> adaptation to different environments, CmeABC is likely subject to control by regulatory elements. We describe the identification of a transcriptional repressor for CmeABC. Insertional mutagenesis of <em>cmeR</em>, an open reading frame immediately upstream of the <em>cmeABC</em> operon, resulted in overexpression of <em>cmeABC</em>, as determined by transcriptional fusion (P_{<em>cmeABC-lacZ</em>}) and immunoblotting with CmeABC-specific antibodies. Overexpression of the efflux pump was correlated with a moderate increase in the level of resistance of the <em>cmeR</em> mutant to several antimicrobials. In vitro, recombinant CmeR bound specifically to the promoter region of <em>cmeABC</em>, precisely, to the inverted repeat sequences in the <em>cmeABC</em> promoter. A single nucleotide deletion between the two half sites of the inverted repeat reduced the level of CmeR binding to the promoter sequence and resulted in overexpression of <em>cmeABC</em>. Together, these findings indicate that <em>cmeR</em> encodes a transcriptional repressor that directly interacts with the <em>cmeABC</em> promoter and modulates the expression of <em>cmeABC</em>. Mutation either in CmeR or in the inverted repeat impedes the repression and leads to enhanced production of the MDR efflux pump.</p>