Role of mexA-mexB-oprM in antibiotic efflux in Pseudomonas aeruginosa

Abstract

We have earlier described mexA-mexB-oprK, an operon involved in pyoverdine export in Pseudomonas aeruginosa, and suggested that the products of these genes also contribute to the active efflux of several antibiotics (K. Poole, K. Krebes, C. McNally, and S. Neshat, J. Bacteriol. 175:7363-7372, 1993). Recently the outer membrane component of this efflux system was shown to be OprM, rather than OprK (N. Gotoh and K. Poole, unpublished results). In the present study, the conclusion concerning the efflux activity of this system was confirmed and extended by the measurement of drug accumulation in intact cells. Thus, the steady-state accumulation levels of tetracycline and norfloxacin were increased in mexA and oprM null mutants. mexA and oprM null mutants also showed an increase in susceptibility to a wide variety of ␤-lactam antibiotics and an increase in the steady-state accumulation level of benzylpenicillin, indicating that the MexA-MexB-OprM pump also effluxes ␤-lactams. Furthermore, deenergization of the cytoplasmic membrane with a proton conductor always produced a strong increase in the accumulation level. Finally, a single-step mutant overproducing MexAB-OprM accumulated less tetracycline and chloramphenicol than the parent strain and was more resistant to a wide range of antimicrobial compounds, including ␤-lactams. These results support the notion that these proteins contribute to the intrinsic resistance of P. aeruginosa through the multidrug active efflux process.Pseudomonas aeruginosa shows significant degrees of intrinsic resistance to a wide variety of antimicrobial agents, including most ␤-lactams, tetracyclines, chloramphenicol, and fluoroquinolones. Although the outer membrane of this species has a very low nonspecific permeability to small, hydrophilic molecules (1, 26), this alone is insufficient to explain the degree of resistance observed (16), and an additional resistance mechanism must be postulated. With some ␤-lactams, hydrolysis of the drugs by the periplasmic ␤-lactamase can serve as this additional mechanism (see reference 18 for a discussion of this phenomenon in Escherichia coli). For other compounds that are not inactivated by wild-type cells, their active efflux out of the cell may be the most likely second contributing factor to resistance (17). Recently, a putative operon, mexA-mexB-oprK, which codes for the export of a siderophore, pyoverdine (20), was suggested to function also as a multidrug efflux pump because overexpression of this operon increased the resistance of P. aeruginosa to chloramphenicol, tetracycline, nalidixic acid, ciprofloxacin, and streptonigrin, and disruption of these genes made the mutants hypersusceptible to these agents (21). (The outer membrane component of this system, previously thought to be the OprK protein seen in the multidrug-resistant strain K385 [21], was shown recently [5], however, to be identical to the previously described protein OprM [12]. Thus, the operon contains genes mexA, mexB, and oprM rather than oprK.) An independent study also show...

Potency of Carbapenems for the Prevention of Carbapenem-Resistant Mutants of Pseudomonas aeruginosa

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Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

“…Other heavy metal salts (analytical grade) were from commercial sources. The sources of antibiotics were as previously described (8,9). Carbonyl cyanide m-chlorophenylhydrazone (CCCP), disodium ATP, and sodium sulfadiazine were purchased from Sigma Chemical Co. (St. Louis, Mo.).…”

Triclocarban Influences Antibiotic Resistance and Alters Anaerobic Digester Microbial Community Structure

“…The mexB gene encodes for the MexB subunit of the MexAB multidrug efflux pump. (36,37) The MexAB system is able to pump antibiotics, organic dyes, detergents, and organic solvents from within a cell and can decrease bacterial susceptibility to several classes of antibiotics and TCS. (37,38) The genera Pseudomonas and Cupriavidus, along with other bacteria, are known to carry the mexB gene.…”