Full Paper Identifi cation and characterization of the AcrR/AcrAB system of a pathogenic Edwardsiella tarda strain

To date several classes of multidrug exporters have been identifi ed in prokaryotic cells, one of which is the resistance nodulation division (RND) family transporters (Poole and Srikumar, 2001). In this type of effl ux system, RND, an inner membrane proton-drug antiporter, forms a tripartite construct with a channel-forming outer membrane protein and an inner membrane protein of the MFP (membrane fusion protein) family (Eswaran et al., 2004). To this class of effl ux pump belongs the AcrAB-TolC complex, in which AcrB, a cytoplasmic protein of the RND family (Yu et al., 2003), cooperates with the outer membrane channel protein TolC (Fralick, 1996; Koronakis et al., 2000; Tikhonova and Zgurskaya, 2004) and the MFP family protein AcrA to form an effl ux pump that is effective against a broad range of antimicrobial agents and toxic compounds, resulting in the Mar (multiple antibiotic resistance) phenotype (Nikaido, 1996; Randall and Woodward, 2002). In Escherichia coli the expression of the acrAB operon is controlled at multiple levels via several distinct mechanisms. On a general scale, it is modulated by stress conditions (Ma et al., 1996) and the XylS/AraC family regulators MarA (Barbosa and Levy, 2000), J. Gen. Appl. Microbiol., 55, 191‒199 (2009)