Substrate Specificities of MexAB-OprM, MexCD-OprJ, and MexXY-OprM Efflux Pumps in Pseudomonas aeruginosa

Abstract

To find the exact substrate specificities of three species of tripartite efflux systems of Pseudomonas aeruginosa, MexAB-OprM, MexCD-OprJ, and MexXY-OprM, we constructed a series of isogenic mutants, each of which constitutively overproduced one of the three efflux systems and lacked the other two, and their isogenic mutants, which lacked all these systems. Comparison of the susceptibilities of the constructed mutants to 52 antimicrobial agents belonging to various groups suggested the following substrate specificities. All of the efflux systems extrude a wide variety of antimicrobial agent groups, i.e., quinolones, macrolides, tetracyclines, lincomycin, chloramphenicol, most penicillins (all but carbenicillin and sulbenicillin), most cephems (all but cefsulodin and ceftazidime), meropenem, and S-4661, but none of them extrude polymyxin B or imipenem. Extrusion of aminoglycosides is specific to MexXY-OprM, and extrusion of a group of the ␤-lactams, i.e., carbenicillin, sulbenicillin, ceftazidime, moxalactam, and aztreonam, is specific to MexAB-OprM. Moreover, MexAB-OprM and MexCD-OprJ extrude novobiocin, cefsulodin, and flomoxef, while MexXY-OprM does not. These substrate specificities are distinct from those reported previously.Several tripartite efflux systems coded on the chromosome play important roles in the intrinsic and acquired resistance in Pseudomonas aeruginosa. Each system consists of a cytoplasmic membrane component of the resistance-nodulation-division family presumed to function as a transporter, an outer membrane component presumed to form channels, and a membrane fusion protein presumed to link the two membrane proteins for reviews, see references (13, 14, and 15). The MexAMexB-OprM efflux system (7, 16) contributes to both intrinsic and acquired resistance in P. aeruginosa, while the MexCMexD-OprJ (17) and MexE-MexF-OprN (6) efflux systems contribute only to the acquired resistance in this bacterium. Studies with mutants that overproduce or lack MexAB-OprM demonstrated that this efflux system extrudes quinolones, macrolides, tetracycline, chloramphenicol, novobiocin, and most ␤-lactams but not imipenem (7,8,22). Studies with mutants overproducing MexCD-OprJ demonstrated that this efflux system extrudes quinolones, erythromycin, tetracycline, chloramphenicol, and expanded-spectrum cephems such as cefpirome (9, 10). Furthermore, characterization of mutants lacking the mexA-mexB-oprM region demonstrated that the MexCD-OprJ efflux system extrudes ceftazidime and cefoperazone as well as cefpirome, while it does not extrude carbenicillin and aztreonam (3). Recently, Aires et al. (1) and our group (12) showed that MexX-MexY extrudes aminoglycosides, tetracycline, and erythromycin in cooperation with spontaneously expressed OprM, thereby contributing to the intrinsic resistance to these agents in P. aeruginosa. Our group also showed that no expression of MexXY is observed in wild-type strains but that the expression can be induced by subinhibitory concentrations of its substrates such as tetracycline a...

Parallel evolution and local differentiation in quinolone resistance in Pseudomonas aeruginosa

“…Approaches such as switching to new antibiotics or using multi-drug cocktails might be effective under one set of conditions but not another, depending on the identity of the second site mutations. In P. aeruginosa, the MexAB-OprM efflux pump (regulated by mexR) extrudes a number of antibiotics, including quinolones, macrolides and b-lactams (Masuda et al, 2000). The MexCD-OprJ efflux pump (regulated by nfxB) also extrudes a variety of antibiotics, but it is ineffective against some b-lactams, such as cephems.…”

Gene cloning and characteristics of the RND-type multidrug efflux pump MuxABC-OpmB possessing two RND components in Pseudomonas aeruginosa

“…However, we were unable to detect a change in the MIC of novobiocin when we disrupted the muxABC-opmB genes in P. aeruginosa PAO1 (data not shown). The reason why an MIC change was not detected in the mux-deleted cells could be that potent novobiocin efflux pumps such as MexAB-OprM and MexCD-OprJ are active enough in PAO1 (Masuda et al, 2000;Schweizer, 2003) to mask the defect of MuxABC-OpmB.…”

Molecular mechanisms of ceftazidime resistance in Pseudomonas aeruginosa isolates from canine and human infections

“…Ceftazidime is an important and effective antimicrobial agent for the therapy of serious infections due to multidrug resistance in P. aeruginosa. A surge in ceftazidime resistance in human clinical isolates of P. aeruginosa results from the production of acquired β-lactamase, the constitutive overproduction of AmpC, or an activation of the MexAB-OprM or MexXY-OprM efflux systems (Lindberg et al, 1987;Li et al, 1994;Stapleton et al, 1995;Nordmann and Guibert, 1998;Aires et al, 1999;Kuga et al, 2000;Masuda et al, 2000;Livermore, 2002). The molecular mechanism of canine ceftazidime resistance in P. aeruginosa isolates still requires further clarification.…”