title: Studies on Acinetobacter baumannii involving multiple mechanisms of carbapenem resistance.
abstract: OBJECTIVE
  Characterize the genetic type and resistance mechanisms of 16 carbapenem-resistant Acinetobacter baumannii (CRAB) isolates recovered between January 2010 and March 2011 from US tertiary-care hospital.
  
  
  RESULTS
  A modified Hodge test demonstrated the presence of carbapenemases, but meropenem and ethylenediaminetetraacetic acid (EDTA) double-disc synergy tests and PCR for metallo-β-lactamase (MBL) genes were negative. The genes of ampC β-lactamase and efflux pump of adeABC and adeIJK were detected. The presence of oxacillinase (OXA)-like genes, blaOXA-51-like , blaOXA-23-like and blaOXA-40-like genes, and insertion sequence ISAba1 in promoter region of blaOXA-51-like and blaOXA-23-like genes were detected; and confirmed by RT-PCR analyses. The sequencing of blaOXA-51-like genes revealed two major alleles, blaOXA-66-like (blaOXA-82 ) and blaOXA-113 from 31·2 to 68·8% of isolates respectively. The blaOXA-23 and blaOXA-72 genes showed high expression and found co-harbouring blaOXA-51-like gene preceded by ISAba-1. All CRAB isolates revealed significant reduction in carO transcription, indicated downregulation of CarO porin system, a potentially independent mechanism of carbapenam resistance. Sequencing of carO gene from representative isolates showed no ISAba1 insertional inactivation. Pulsed-field gel electrophoresis revealed a clonal relationship.
  
  
  CONCLUSIONS
  CRAB exhibited diversity of mechanisms of carbapenem resistance, and clonal relationship.
  
  
  CONCLUSIONS
  Studies on distinct outbreaks of CRAB are alarming situation for clinicians.
authors.affiliation: Department of Microbiology and Immunology, Center for Surgical Infections and Biofilms, Drexel University, Philadelphia, 19102, PA, USA.
authors.forename: B
authors.initials: B
authors.lastname: Sen
authors.affiliation: Department of Microbiology and Immunology, Center for Surgical Infections and Biofilms, Drexel University, Philadelphia, 19102, PA, USA.|School of Biomedical Engineering, Science and Health Systems, Center for Surgical Infections and Biofilms, Drexel University, Philadelphia, 19102, PA, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Joshi
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015780:Carbapenems / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D015780:Carbapenems; D001618:beta-Lactamases; C063912:carbapenemase; C108449:oxacillinase
keywords: Acinetobacter baumannii; ISAba insertion sequence; OXA-type β-lactamase; ampC β-lactamase; carO gene; carbapenem resistance; drug efflux pump; pulsed-field gel electrophoresis