title: Heterogeneous persister cells formation in Acinetobacter baumannii.
abstract: Bacterial persistence is a feature that allows susceptible bacteria to survive extreme concentrations of antibiotics and it has been verified in a number of species, such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus spp., Mycobacterium spp. However, even though Acinetobacter baumannii is an important nosocomial pathogen, data regarding its persistence phenotype are still lacking. Therefore, the aim of this study was to evaluate the persistence phenotype in A. baumannii strains, as well as its variation among strains after treatment with polymyxin B and tobramycin. Stationary cultures of 37 polymyxin B-susceptible clinical strains of A. baumannii were analyzed for surviving cells after exposure to 15 µg/mL of polymyxin B for 6 h, by serial dilutions and colony counting. Among these, the 30 tobramycin-susceptible isolates also underwent tobramycin treatment at a concentration of 160 µg/mL and persister cells occurrence was evaluated equally. A high heterogeneity of persister cells formation patterns among isolates was observed. Polymyxin B-treated cultures presented persister cells corresponding from 0.0007% to 10.1% of the initial population and two isolates failed to produce detectable persister cells under this condition. A high variability could also be observed when cells were treated with tobramycin: the persister fraction corresponded to 0.0003%-11.84% of the pre-treatment population. Moreover, no correlation was found between persister subpopulations comparing both antibiotics among isolates, indicating that different mechanisms underlie the internal control of this phenotype. This is the first report of persister cells occurrence in A. baumannii. Our data suggest that distinct factors regulate the tolerance for unrelated antibiotics in this species, contrasting the multi-drug tolerance observed in other species (eg. dormancy-mediated tolerance). Supporting this observation, polymyxin B--an antibiotic that is believed to act on non-dividing cells as well--failed to eradicate persister cells in the majority of the isolates, possibly reflecting a disconnection between persistence and dormancy.
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Valdir Cristóvão
authors.initials: VC
authors.lastname: Barth
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Belisa Ávila
authors.initials: BÁ
authors.lastname: Rodrigues
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Grasiela Daiane
authors.initials: GD
authors.lastname: Bonatto
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Stephanie Wagner
authors.initials: SW
authors.lastname: Gallo
authors.affiliation: Departamento de Microbiologia do Laboratório de Patologia Clínica, Hospital São Lucas, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Vany Elisa
authors.initials: VE
authors.lastname: Pagnussatti
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Carlos Alexandre Sanchez
authors.initials: CA
authors.lastname: Ferreira
authors.affiliation: Laboratório de Imunologia e Microbiologia, Faculdade de Biociências, Pontifícia Universidade do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Sílvia Dias
authors.initials: SD
authors.lastname: de Oliveira
mesh_terms: D040981:Acinetobacter baumannii / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D050296:Microbial Viability / Q000187:drug effects*; D010641:Phenotype; D011112:Polymyxin B / Q000494:pharmacology; D013045:Species Specificity; D014031:Tobramycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D011112:Polymyxin B; D014031:Tobramycin