title: Molecular characterization and antimicrobial susceptibility of Acinetobacter baumannii isolates obtained from two hospital outbreaks in Los Angeles County, California, USA.
abstract: BACKGROUND
  Antibiotic resistant strains of Acinetobacter baumannii have been responsible for an increasing number of nosocomial infections including bacteremia and ventilator-associated pneumonia. In this study, we analyzed 38 isolates of A. baumannii obtained from two hospital outbreaks in Los Angeles County for the molecular epidemiology, antimicrobial susceptibility and resistance determinants.
  
  
  METHODS
  Pulsed field gel electrophoresis, tri-locus multiplex PCR and multi-locus sequence typing (Pasteur scheme) were used to examine clonal relationships of the outbreak isolates. Broth microdilution method was used to determine antimicrobial susceptibility of these isolates. PCR and subsequent DNA sequencing were employed to characterize antibiotic resistance genetic determinants.
  
  
  RESULTS
  Trilocus multiplex PCR showed these isolates belong to Global Clones I and II, which were confirmed to ST1 and ST2, respectively, by multi-locus sequence typing. Pulsed field gel electrophoresis analysis identified two clonal clusters, one with 20 isolates (Global Clone I) and the other with nine (Global Clone II), which dominated the two outbreaks. Antimicrobial susceptibility testing using 14 antibiotics indicated that all isolates were resistant to antibiotics belonging to four or more categories of antimicrobial agents. In particular, over three fourth of 38 isolates were found to be resistant to both imipenem and meropenem. Additionally, all isolates were found to be resistant to piperacillin, four cephalosporin antibiotics, ciprofloxacin and levofloxacin. Resistance phenotypes of these strains to fluoroquinolones were correlated with point mutations in gyrA and parC genes that render reduced affinity to target proteins. ISAba1 was detected immediately upstream of the bla OXA-23 gene present in those isolates that were found to be resistant to both carbapenems. Class 1 integron-associated resistance gene cassettes appear to contribute to resistance to aminoglycoside antibiotics.
  
  
  CONCLUSIONS
  The two outbreaks were found to be dominated by two clonal clusters of A. baumannii belonging to MLST ST1 and ST2. All isolates were resistant to antibiotics of at least four categories of antimicrobial agents, and their antimicrobial susceptibility profiles correlate well with genetic determinants. The results of this study will facilitate our understanding of the molecular epidemiology, antimicrobial susceptibility and mechanisms of resistance of A. baumannii obtained from Los Angeles hospitals.
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Warner
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Shan N
authors.initials: SN
authors.lastname: Kuang
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Rina
authors.initials: R
authors.lastname: Hernandez
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Melissa C
authors.initials: MC
authors.lastname: Chong
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ewing
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Jen
authors.initials: J
authors.lastname: Fleischer
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Meng
authors.affiliation: Los Angeles County Department of Public Health, Public Health Laboratory, Los Angeles, CA, 90242, USA.
authors.forename: Sheena
authors.initials: S
authors.lastname: Chu
authors.affiliation: Los Angeles County Department of Public Health, Los Angeles, CA, 90012, USA.
authors.forename: Dawn
authors.initials: D
authors.lastname: Terashita
authors.affiliation: Los Angeles County Department of Public Health, Los Angeles, CA, 90012, USA.
authors.forename: L'Tanya
authors.initials: L
authors.lastname: English
authors.affiliation: Human Health Therapeutics, National Research Council Canada, Ottawa, ON, K1A 0R6, Canada.
authors.forename: Wangxue
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, Los Angeles, California, 90032, USA. hxu3@calstatela.edu.
authors.forename: H Howard
authors.initials: HH
authors.lastname: Xu
mesh_terms: D000151:Acinetobacter Infections / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002140:California; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV; D004196:Disease Outbreaks; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D032023:Integrons; D007362:Intensive Care Units; D008826:Microbial Sensitivity Tests; D058885:Multilocus Sequence Typing; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001618:beta-Lactamases; C000599728:beta-lactamase OXA-23, Acinetobacter baumannii; C410345:beta-lactamase OXA-24; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase
keywords: Acinetobacter baumannii; Antimicrobial susceptibility; Epidemiology; Mechanism of resistance; Nosocomial outbreak