title: Diversity of polymyxin resistance mechanisms among Acinetobacter baumannii clinical isolates.
abstract: Polymyxins have become drugs of last resort for treatment of multi-drug resistant (MDR) Gram-negative infections. However, the mechanisms of resistance to this compound have not been completely elucidated. In this study, we evaluated the mechanisms of resistance to this antimicrobial in two A. baumannii clinical isolates, respectively, susceptible (A027) and resistant (A009) to polymyxin B before and after polymyxin B exposure (A027indand A009ind). The pmrAB and lpxACD were sequenced and their transcriptional levels were analyzed by qRT-PCR. The bacterial cell morphology was evaluated by transmission electronic microscopy (TEM) and the membrane potential was measured using Zeta-potential analyzer. The virulence of strains was studied using a Caenorhabditis elegans model. Both clinical isolates exhibited an elevation of the polymyxin B MIC after exposure to this compound. On the other hand, A027indshowed decreased values of MIC for β-lactams, aminoglycosides, vancomycin, teicoplanin, oxacillin and erythromycin. A027indharbored two mutations in pmrB and the ISAba125 disrupting the lpxA. In contrast, A009indstrain exhibited increase of pmrB transcriptional level, after polymyxin B exposure, despite the absence of mutations in the pmrAB genes. The TEM images revealed a thicker and more electron-dense peptidoglycan layer for A009 than that of A027. The exposure to polymyxin B induced a strong condensation and darkening of intracellular material, mainly in A009ind. In addition, the surface charge of A009 was significantly less negative than the one of A027. Using the C. elegans model, only A027indstrain showed a reduction on virulence. The diversity of polymyxin B resistance mechanisms among A. baumannii strains evaluated in this study confirms the complexity of these mechanisms, which may vary depending of the background of each strain.
authors: Laboratório Alerta, Disciplina de Infectologia, Departamento de Medicina, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brazil. Electronic address: raquelgirardello@gmail.com.
authors: Raquel
authors: R
authors: Girardello
authors: Laboratório Alerta, Disciplina de Infectologia, Departamento de Medicina, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brazil.
authors: Marina
authors: M
authors: Visconde
authors: Laboratório Alerta, Disciplina de Infectologia, Departamento de Medicina, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brazil.
authors: Rodrigo
authors: R
authors: Cayô
authors: Departamento de Microbiologia, Fundação Oswaldo Cruz, Centro de Pesquisas Aggeu Magalhães, Recife, Pernambuco, Brazil.
authors: Regina Célia Bressan Queiroz de
authors: RC
authors: Figueiredo
authors: Departamento de Biofísica, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brazil.
authors: Marcelo Alves da Silva
authors: MA
authors: Mori
authors: Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo - USP, São Paulo, SP, Brazil; Departamento de Análises Clínicas e Toxicológicas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo - USP, São Paulo, SP, Brazil.
authors: Nilton
authors: N
authors: Lincopan
authors: Laboratório Alerta, Disciplina de Infectologia, Departamento de Medicina, Universidade Federal de São Paulo - UNIFESP, São Paulo, SP, Brazil.
authors: Ana Cristina
authors: AC
authors: Gales
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification / Q000648:ultrastructure; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017173:Caenorhabditis elegans / Q000382:microbiology / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D005798:Genes, Bacterial; D014644:Genetic Variation; D006801:Humans; D008564:Membrane Potentials; D008826:Microbial Sensitivity Tests; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D011113:Polymyxins / Q000494:pharmacology*; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D016019:Survival Analysis; D014774:Virulence
chemical_list: D000900:Anti-Bacterial Agents; D011113:Polymyxins
keywords: A. baumannii; Polymyxin resistance; Virulence