title: Screening of mutator phenotype in clinical strains of Acinetobacter baumannii.
abstract: To our knowledge, no study has considered the growing colonies of A. baumannii in the inhibition zone of antibiotic disks as an indication of mutator. Here, we screened the mutator phenotype in a large series of clinical strains of A. baumannii. A collection of 300 strains were tested for antibiotic susceptibility and yielding colonies in the inhibition zone of antibiotic disks. The mutation frequency (MF) of strains was determined using rifampicin screen agar (300 μg/mL). Among strains tested, 180 had colonies in the inhibition zone of at least one or more than one (≤7) antibiotic. Sixty strains also generated mutant colonies on rifampicin screen agar with MF mean of 4.9 × 10-9. One strain was found with 59-fold (2.9 × 10-7) increase of MF than the mean value, only yielded colonies in the inhibition zone of imipenem, and classified as strong mutator or hypermutator. The MF ranged from 1 × 10-12to 6.6 × 10-10in remaining strains (n = 59), corresponded to non-mutator phenotype. There was a significant correlation between the number of colonies that grew in inhibition zone of amikacin disk and MF (P = 0.002). We showed that mutator phenotype emerged among clinical strains of A. baumannii as expected frequency in other bacterial species from non-chronic infections. This study revealed that wide screening of strains yielding colonies in the inhibition zone of antibiotics can be utilized to identify mutators. The mutant colonies need to be considered as a subpopulation of bacteria that may affect the interpretation of antibiotic susceptibility testing and consequently lead to treatment failure.
authors.affiliation: Division of Microbiology, Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Behnaz
authors.initials: B
authors.lastname: Deiham
authors.affiliation: Division of Microbiology, Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran; Food Microbiology Research Center, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: mdouraghi@tums.ac.ir.
authors.forename: Masoumeh
authors.initials: M
authors.lastname: Douraghi
authors.affiliation: Division of Microbiology, Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Habibeh
authors.initials: H
authors.lastname: Adibhesami
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Yaseri
authors.affiliation: Department of Microbiology, Reference Health Laboratories, Ministry of Health, Tehran, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Rahbar
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000235:genetics* / Q000302:isolation & purification*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial; D006801:Humans; D008403:Mass Screening; D009154:Mutation; D059645:Mutation Rate; D010641:Phenotype; D062606:Tertiary Care Centers
chemical_list: D000900:Anti-Bacterial Agents
keywords: Acinetobacter baumannii; Antibiotic resistance; Mutation frequency; Mutator; Rifampicin