title: Mutations in NalC induce MexAB-OprM overexpression resulting in high level of aztreonam resistance in environmental isolates of Pseudomonas aeruginosa.
abstract: Pseudomonas aeruginosa is an opportunistic pathogen with high resistance to a wide variety of antimicrobials. The multidrug resistance pump MexAB-OprM promotes the efflux of various antibiotics, mostly when mutations accumulate in the transcriptional regulators MexR, NalC and NalD, thereby causing MexAB-OprM overexpression. In this work, a characterization of 50 P. aeruginosa isolates obtained from Brazilian agricultural soils to determine the reasons of their resistance to aztreonam was done. The majority of the isolates showed higher aztreonam resistance than wild-type strain by MIC method. DNA sequence analysis of mexR, nalC and nalD genes from 13 of these isolates showed the amino acid substitution in NalC for all tested isolates, just one mutation was detected in MexR and none in NalD. Furthermore, an increase in the level of mexA expression by real-time RT-PCR analysis in eight isolates harboring mutations in NalC was found. Although there was not a relationship between MIC of aztreonam and the level of mexA expression, on the other hand, the results presented here suggest that novel mutations in NalC, including Arg97-Gly and Ala186-Thr, are related to MexAB-OprM overexpression causing aztreonam resistance in P. aeruginosa environmental isolates.
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N. Monte Alegre, Ribeirão Preto, SP 14040-903, Brazil.
authors.forename: Vânia S
authors.initials: VS
authors.lastname: Braz
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N. Monte Alegre, Ribeirão Preto, SP 14040-903, Brazil.
authors.forename: João Pedro R
authors.initials: JP
authors.lastname: Furlan
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N. Monte Alegre, Ribeirão Preto, SP 14040-903, Brazil.
authors.forename: Ana Flavia T
authors.initials: AF
authors.lastname: Fernandes
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N. Monte Alegre, Ribeirão Preto, SP 14040-903, Brazil eliana.stehling@gmail.com.
authors.forename: Eliana G
authors.initials: EG
authors.lastname: Stehling
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001398:Aztreonam / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000235:genetics; D001938:Brazil; D024901:Drug Resistance, Multiple, Bacterial; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009876:Operon; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012988:Soil Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; D001398:Aztreonam
keywords: MexAB-OprM; NalC; Pseudomonas aeruginosa; antimicrobial resistance; aztreonam; soil