Variation of the mexT gene, a regulator of the MexEF-OprN efflux pump expression in wild-type strains of Pseudomonas aeruginosa

Maseda, Hideaki; Saito, Kohjiro; Nakajima, Akira; Nakae, Taiji

doi:10.1111/j.1574-6968.2000.tb09367.x

Cited by 118 publications

(88 citation statements)

References 22 publications

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“…Transformation of mexT-P1 into MPAO1-P2 reverted the strain back to the P1 phenotype. The phenotypes of P. aeruginosa that are similar to P1 and P2 have been previously described (4)(5)(6)(7). In the cited studies, the wild-type PAO1 strain harbored an 8-bp insertion in mexT that results in a nonfunctional MexT protein and a phenotype similar to P2.…”

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confidence: 77%

“…In the cited studies, the wild-type PAO1 strain harbored an 8-bp insertion in mexT that results in a nonfunctional MexT protein and a phenotype similar to P2. Its derivative mutant that was selected by norfloxacin (referred to as a nfxC-type mutant) had a functional MexT protein and was characterized by attenuated pyocyanin production (5), high resistance to chloramphenicol (6), and absence of swarming motility (8) similar to the P1 strains in our study (3). mexT has been described as a mutational "hot spot," where mutations can contribute to global phenotypic changes in P. aeruginosa (6,(9)(10)(11).…”

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confidence: 97%

“…Its derivative mutant that was selected by norfloxacin (referred to as a nfxC-type mutant) had a functional MexT protein and was characterized by attenuated pyocyanin production (5), high resistance to chloramphenicol (6), and absence of swarming motility (8) similar to the P1 strains in our study (3). mexT has been described as a mutational "hot spot," where mutations can contribute to global phenotypic changes in P. aeruginosa (6,(9)(10)(11). MexT is a transcriptional regulator of the MexEF-OprN efflux pump, which has been extensively characterized in the context of antimicrobial agents (12-15).…”

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Emergence of the P2 Phenotype in Pseudomonas aeruginosa PAO1 Strains Involves Various Mutations in mexT or mexF

Luong

Shogan

Zaborin

et al. 2013

Journal of Bacteriology

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We recently demonstrated that Pseudomonas aeruginosa PAO1 undergoes a pronounced phenotypic change when introduced into the intestines of rats during surgical injury. Recovered strains displayed a specific phenotype (termed the P2 phenotype) characterized by altered pyocyanin production, high collagenase activity, high swarming motility, low resistance to chloramphenicol, and increased killing of Caenorhabditis elegans compared to the inoculating strain (termed the P1 phenotype). The aims of this study were to characterize the differences between the P. aeruginosa P1 and P2 phenotypes in quorum sensing and competitiveness. We then determined the presence of the P2 phenotype among PAO1 strains from various laboratories. Results demonstrated that P2 cells display accelerated growth during early exponential phase and early activation of quorum-sensing systems and overcome the growth of P1 cells in a mixed population. Among eight PAO1 strains obtained from different laboratories, four exhibited the P2 phenotype. Of 27 mutants analyzed from the P. aeruginosa MPAO1 transposon library, 25 displayed P2 phenotypes. The P2 phenotype in both cases correlated with a lack of expression of mexE or mexF due to mutations in mexT and mexF genes. In summary, strains possessing the P2 phenotype are distributed among PAO1 strains commonly used across a variety of research laboratories. Genetically, they are characterized by various mutations in mexT or mexF. Stable genetic mutations that change phenotypes can arise as microbes adapt to their environment to maximize propagation. This ecologically dependent shift in phenotype has been documented in many bacterial species and in diverse contexts (1, 2). Recently, we demonstrated that the MPAO1 strain of Pseudomonas aeruginosa became transformed to (or selected for) a more virulent phenotype when present in the colon of rats subjected to preoperative radiation followed by colon resection and anastomosis (3). The strain recovered from the anastomotic tissue (termed MPAO1-P2, i.e., having the P2 phenotype) exhibited high collagenase activity, swarming ability, increased pyocyanin production in liquid medium, and increased tissue-destroying capacity compared to the initial strain (termed MPAO1-P1, having the P1 phenotype). Comparative genomic sequencing analysis revealed that MPAO1-P2 harbored a single-nucleotide polymorphism (SNP) in the mexT gene that results in a truncated and nonfunctional MexT protein. Transformation of mexT-P1 into MPAO1-P2 reverted the strain back to the P1 phenotype. The phenotypes of P. aeruginosa that are similar to P1 and P2 have been previously described (4-7). In the cited studies, the wild-type PAO1 strain harbored an 8-bp insertion in mexT that results in a nonfunctional MexT protein and a phenotype similar to P2. Its derivative mutant that was selected by norfloxacin (referred to as a nfxC-type mutant) had a functional MexT protein and was characterized by attenuated pyocyanin production (5), high resistance to chloramphenicol (6), and absence of swarming ...

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confidence: 77%

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confidence: 97%

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confidence: 99%

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Emergence of the P2 Phenotype in Pseudomonas aeruginosa PAO1 Strains Involves Various Mutations in mexT or mexF

Luong

Shogan

Zaborin

et al. 2013

Journal of Bacteriology

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“…The LysR-type regulator MexT is involved in controlling the expression of multiple genes in nfxC mutants, including mexEF-oprN, oprD, and genes for virulence factors (836,(841)(842)(843)(844). mexT variations have been observed in wild-type strains and MexEF-OprN-hyperproducing nfxC mutants, which possess inactive and active forms of MexT, respectively (845). One gene of the MexT regulon, mexS (encoding an oxidoreductase of unknown function [836]), is of particular importance, as its alteration in nfxC mutants induces mexEF-oprN expression with concomitant development of MDR (846).…”

Section: P Aeruginosa Efflux Pumpsmentioning

confidence: 99%

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

2015

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SUMMARY The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.

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“…In some drug-susceptible laboratory strains of the PAO1 lineage, mexT is inactivated by an 8-bp insert (7). Spontaneous excision of this intragenic fragment restores the open reading frame of mexT with the concomitant overexpression of mexEF-oprN and the development of the typical NfxC phenotype (6).…”

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Amino Acid Substitutions Account for Most MexS Alterations in Clinical nfxC Mutants of Pseudomonas aeruginosa

Richardot

Juarez

Jeannot

et al. 2016

Antimicrob Agents Chemother

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bMultidrug-resistant mutants of Pseudomonas aeruginosa that overproduce the active efflux system MexEF-OprN (called nfxC mutants) have rarely been characterized in the hospital setting. Screening of 221 clinical strains exhibiting a reduced susceptibility to ciprofloxacin (a substrate of MexEF-OprN) and imipenem (a substrate of the negatively coregulated porin OprD) led to the identification of 43 (19.5%) nfxC mutants. Subsequent analysis of 22 nonredundant mutants showed that, in contrast to their in vitro-selected counterparts, only 3 of them (13.6%) harbored a disrupted mexS gene, which codes for the oxidoreductase MexS, whose inactivation is known to activate the mexEF-oprN operon through a LysR-type regulator, MexT. Nine (40.9%) of the clinical nfxC mutants contained single amino acid mutations in MexS, and these were associated with moderate effects on resistance and virulence factor production in 8/9 strains. Finally, the remaining 10 (45.5%) nfxC mutants did not display mutations in any of the regulators known to control mexEF-oprN expression (the mexS, mexT, mvaT, and ampR genes), confirming that other loci are responsible for pump upregulation in patients. Collectively, these data demonstrate that nfxC mutants are probably more frequent in the hospital than previously thought and have genetic and phenotypic features somewhat different from those of in vitro-selected mutants. Pseudomonas aeruginosa is a notorious cause of acute and chronic infections in vulnerable patients. The ability of this environmental Gram-negative bacterium to produce a broad range of virulence factors (1) and to become resistant to multiple antimicrobial agents is considered a key to its success in the hospital setting. When overexpressed upon mutation, several efflux systems belonging to the resistance-nodulation-cell division (RND) family of drug transporters are able to decrease the susceptibility of the pathogen to structurally unrelated antibiotics (2). One of these systems, named MexEF-OprN, is quiescent in wildtype strains grown under standard laboratory conditions. Its contribution to the intrinsic resistance of P. aeruginosa is therefore minimal. In contrast, in so-called nfxC mutants, stable overproduction of the pump results in a significant increase in the MICs (4-to 16-fold) of chloramphenicol, trimethoprim, and fluoroquinolones (3). Compared with the susceptibility of wild-type strains, typical nfxC mutants exhibit a hypersusceptibility to some antipseudomonal ␤-lactams (penicillins, cephalosporins) and aminoglycosides, a phenotype possibly due to the impaired activity of two other RND pumps, namely, MexAB-OprM and MexXY/ OprM (4). Furthermore, this typical NfxC phenotype includes a decreased susceptibility to carbapenems, linked to the downregulation of the oprD gene, which codes for the specific porin OprD, allowing the facilitated diffusion of these antibiotics into the cell (3).In P. aeruginosa, while most RND pumps have their expression modulated by repressors (5), transcription of the mexEF-oprN operon is con...

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Variation of the mexT gene, a regulator of the MexEF-OprN efflux pump expression in wild-type strains of Pseudomonas aeruginosa

Cited by 118 publications

References 22 publications

Emergence of the P2 Phenotype in Pseudomonas aeruginosa PAO1 Strains Involves Various Mutations in mexT or mexF

Emergence of the P2 Phenotype in Pseudomonas aeruginosa PAO1 Strains Involves Various Mutations in mexT or mexF

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

Amino Acid Substitutions Account for Most MexS Alterations in Clinical nfxC Mutants of Pseudomonas aeruginosa

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