title: Prevalence of hypermutators among clinical Acinetobacter baumannii isolates.
abstract: OBJECTIVE
  The objectives of this study were to study the presence of mutators in a set of Acinetobacter baumannii isolates and to explore whether there is a correlation between mutation rates and antibiotic resistance.
  
  
  METHODS
  The variation in mutation rate was evaluated for 237 clinical A. baumannii isolates by determining the frequency of their mutation to rifampicin resistance. For each isolate, the antibiotic resistance profile was determined by disc diffusion and/or Etest. Isolates were divided into susceptible, resistant and MDR groups according to their resistance to five groups of different antibiotics. A comparison between differences in mutation frequency (f) and strain-specific factors was performed.
  
  
  RESULTS
  Of the 237 isolates 32%, 18% and 50% were classified as susceptible, resistant and MDR, respectively. The f of rifampicin resistance varied between 2.2 × 10(-10) and 1.2 × 10(-6). Of the strains under investigation, 16% had an ≥2.5- to 166-fold higher f. The presence of mutators (definition ≥2.5-fold increase in f compared with ATCC 19606) in the MDR group (22%) was significantly higher (P < 0.05) than that in the susceptible and resistant groups (11% and 7%, respectively). Furthermore, f was significantly higher in the MDR group compared with that in the susceptible and resistant groups.
  
  
  CONCLUSIONS
  The facts that 26 of 37 mutator isolates (70%) in the population were MDR and that there was a significantly higher general f in isolates exhibiting an MDR profile suggest that hypermutability can be of advantage for the organism in a selective environment with extensive exposure to antimicrobials.
authors.affiliation: Department of Medical Sciences, Section of Infectious Diseases, University of Uppsala, 75105 Uppsala, Sweden patriciakomplindgren@gmail.com.
authors.forename: Patricia
authors.initials: P
authors.lastname: Komp Lindgren
authors.affiliation: Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, 50935 Cologne, Germany.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Higgins
authors.affiliation: Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, 50935 Cologne, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Seifert
authors.affiliation: Department of Medical Sciences, Section of Infectious Diseases, University of Uppsala, 75105 Uppsala, Sweden.
authors.forename: Otto
authors.initials: O
authors.lastname: Cars
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial; D059645:Mutation Rate; D012293:Rifampin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D012293:Rifampin