title: NagZ-dependent and NagZ-independent mechanisms for β-lactamase expression in Stenotrophomonas maltophilia.
abstract: 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 was characterized, and its roles in basal-level β-lactamase derepression, induced β-lactamase activities, and β-lactam resistance of KJΔDI, KJΔmrcA, and KJΔDIΔmrcA were evaluated. Expression of the nagZ gene was constitutive and not regulated by AmpR, AmpD(I), AmpN, AmpG, PBP1a, and NagZ. Introduction of ΔnagZ into KJΔDI nearly abolished basal-level derepressed β-lactamase activity; conversely, introduction of ΔnagZ into KJΔmrcA did not affect it. At least two activator ligands (ALs) are thus considered responsible for β-lactamase expression in the S. maltophilia system, specifically, the NagZ-dependent (AL1) and NagZ-independent (AL2) ligands responsible for the basal-level derepressed β-lactamase activities of KJΔDI and KJΔmrcA, respectively. The contributions of AL1 and AL2 to the induced β-lactamase activities may vary with the types of β-lactams. nagZ inactivation did not affect aztreonam-, cefoxitin-, and carbenicillin-induced β-lactamase activities, but it attenuated cefuroxime- and piperacillin-induced β-lactamase activities. Introduction of ΔnagZ into KJ, KJΔDI, KJΔmrcA, and KJΔDIΔmrcA did not significantly change the MICs of the β-lactams tested except that the MICs of cefuroxime and piperacillin moderately decreased in strains KJΔZ and KJΔDIΔZ (nagZ mutants).
authors.affiliation: Graduate Institute of Microbiology and Public Health, National Chung-Hsing University, Taichung, Taiwan.
authors.forename: Yi-Wei
authors.initials: YW
authors.lastname: Huang
authors.forename: Rouh-Mei
authors.initials: RM
authors.lastname: Hu
authors.forename: Cheng-Wen
authors.initials: CW
authors.lastname: Lin
authors.forename: Tung-Ching
authors.initials: TC
authors.lastname: Chung
authors.forename: Tsuey-Ching
authors.initials: TC
authors.lastname: Yang
mesh_terms: D000118:Acetylglucosaminidase / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D050557:Catechol 2,3-Dioxygenase / Q000378:metabolism; D003001:Cloning, Molecular; D017931:DNA Primers; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000502:physiology; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics; D010957:Plasmids; D016133:Polymerase Chain Reaction; D018085:Regulon; D020615:Stenotrophomonas maltophilia / Q000201:enzymology* / Q000235:genetics*; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D017931:DNA Primers; D047090:beta-Lactams; D050557:Catechol 2,3-Dioxygenase; D000118:Acetylglucosaminidase; C062460:AmpD protein, Bacteria; D009238:N-Acetylmuramoyl-L-alanine Amidase; D001618:beta-Lactamases