Dataset Information

NagZ-dependent and NagZ-independent mechanisms for ?-lactamase expression in Stenotrophomonas maltophilia.

ABSTRACT: ?-N-Acetylglucosaminidase (NagZ), encoded by the nagZ gene, is a critical enzyme for basal-level ampC derepression (ampC expression in the absence of ?-lactam challenge) in ampD and dacB mutants of Pseudomonas aeruginosa. Three mutants with a phenotype of basal-level L1 and L2 ?-lactamase derepression in Stenotrophomonas maltophilia have been reported, including KJ?DI (ampD(I) mutant), KJ?mrcA (mrcA mutant), and KJ?DI?mrcA (ampD(I) and mrcA double mutant). In this study, nagZ of S. maltophilia was characterized, and its roles in basal-level ?-lactamase derepression, induced ?-lactamase activities, and ?-lactam resistance of KJ?DI, KJ?mrcA, and KJ?DI?mrcA were evaluated. Expression of the nagZ gene was constitutive and not regulated by AmpR, AmpD(I), AmpN, AmpG, PBP1a, and NagZ. Introduction of ?nagZ into KJ?DI nearly abolished basal-level derepressed ?-lactamase activity; conversely, introduction of ?nagZ into KJ?mrcA did not affect it. At least two activator ligands (ALs) are thus considered responsible for ?-lactamase expression in the S. maltophilia system, specifically, the NagZ-dependent (AL1) and NagZ-independent (AL2) ligands responsible for the basal-level derepressed ?-lactamase activities of KJ?DI and KJ?mrcA, respectively. The contributions of AL1 and AL2 to the induced ?-lactamase activities may vary with the types of ?-lactams. nagZ inactivation did not affect aztreonam-, cefoxitin-, and carbenicillin-induced ?-lactamase activities, but it attenuated cefuroxime- and piperacillin-induced ?-lactamase activities. Introduction of ?nagZ into KJ, KJ?DI, KJ?mrcA, and KJ?DI?mrcA did not significantly change the MICs of the ?-lactams tested except that the MICs of cefuroxime and piperacillin moderately decreased in strains KJ?Z and KJ?DI?Z (nagZ mutants).

SUBMITTER: Huang YW

PROVIDER: S-EPMC3318340 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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NagZ-dependent and NagZ-independent mechanisms for β-lactamase expression in Stenotrophomonas maltophilia.

Huang Yi-Wei YW Hu Rouh-Mei RM Lin Cheng-Wen CW Chung Tung-Ching TC Yang Tsuey-Ching TC

Antimicrobial agents and chemotherapy 20120117 4

β-N-Acetylglucosaminidase (NagZ), encoded by the nagZ gene, is a critical enzyme for basal-level ampC derepression (ampC expression in the absence of β-lactam challenge) in ampD and dacB mutants of Pseudomonas aeruginosa. Three mutants with a phenotype of basal-level L1 and L2 β-lactamase derepression in Stenotrophomonas maltophilia have been reported, including KJΔDI (ampD(I) mutant), KJΔmrcA (mrcA mutant), and KJΔDIΔmrcA (ampD(I) and mrcA double mutant). In this study, nagZ of S. maltophilia w ...[more]

PMID: 22252801

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Project description:Intrinsic β-lactam resistance in Stenotrophomonas maltophilia is caused by bla L1 and/or bla L2, a kind of metallo-β-lactamase with a broad substrate spectrum including carbapenems. A rapid and sensitive molecular method for the detection of bla L1 in clinical samples is needed to guide therapeutic treatment. In present study, we first described a loop-mediated isothermal amplification (LAMP) method for the rapid detection of bla L1 in clinical samples by using two methods including a chromogenic method using calcein/Mn(2+) complex and the real-time turbidity monitoring to assess the reaction. Then dissemination of L1-producing S. maltophilia was investigated from ICU patients in three top hospital in Beijing, China. The results showed that both methods detected the target DNA within 60 min under isothermal conditions (65°C). The detection limit of LAMP was 3.79 pg/μl DNA, and its sensitivity 100-fold greater than that of conventional PCR. All 21 test strains except for S. maltophilia were negative for bla L1, indicative of the high-specificity of the primers for the bla L1. A total of 22 L1-positive isolates were identified for LAMP-based surveillance of bla L1 from 105 ICU patients with clinically suspected multi-resistant infections. The sequences of these bla L1 genes were conservative with only a few sites mutated, and the strains had highly resistant to β-lactam antibiotics. The MLST recovered that 22 strains belonged to seven different S. maltophilia sequence types (STs). Furthermore, co-occurrence of bla L1 and bla L2 genes were detected in all of isolates. Strikingly, S. maltophilia DCPS-01 was recovered to contain bla L1, bla L2, and bla NDM-1 genes, possessing an ability to hydrolyse all β-lactams antibiotics. Our data showed the diversity types of S. maltophilia carrying bla L1 and co-occurrence of many resistant genes in the clinical strains signal an ongoing and fast evolution of S. maltophilia resulting from their wide spread in the respiratory infections, and therefore will be difficult to control.

Dataset Information

NagZ-dependent and NagZ-independent mechanisms for ?-lactamase expression in Stenotrophomonas maltophilia.

Publications

NagZ-dependent and NagZ-independent mechanisms for β-lactamase expression in Stenotrophomonas maltophilia.

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