title: Molecular Characterization of Invasive Carbapenem-Resistant Acinetobacter baumannii from a Tertiary Care Hospital in South India.
abstract: BACKGROUND
  Acinetobacter baumannii is an important opportunistic pathogen responsible for causing nosocomial infections. Carbapenems are considered to be the drug of choice to treat infections caused by multidrug-resistant A. baumannii. The prevalent mechanism of carbapenem resistance in A. baumannii is enzymatic degradation by β-lactamases. Therefore, the aim of the study is to determine the prevalence and distribution of molecular determinants among the clinical isolates of carbapenem-resistant A. baumannii.
  
  
  METHODS
  A total of 103 consecutive, non-duplicate carbapenem-resistant A. baumannii isolated from blood and endotracheal aspirates (ETAs) were included in the study. The CarbAcineto NP test was performed for the screening of carbapenemase production. Polymerase chain reaction (PCR) was performed to detect extended spectrum β-lactamases (ESBLs), metallo-β-lactamases (MBLs) and oxacillinases (OXAs). PCR was done for the detection of ISAba1 elements, and mapping PCR was performed to identify the position of ISAba1 with respect to the OXA-23-like gene.
  
  
  RESULTS
  Among the 103 A. baumannii isolates, 94 were phenotypically identified as carbapenemase producers. blaPER was the most common among the ESBLs. Among MBLs, blaNDM was predominant followed by the blaVIM gene. blaOXA-51 and blaOXA-23 were the most common and present in all 103 isolates. Almost 80% of the isolates had ISAba1 upstream blaOXA-23 gene.
  
  
  CONCLUSIONS
  The blaOXA-23 and blaNDM genes are the most common type of oxacillinases and metallo β-lactamases, respectively, and contribute to carbapenem resistance in clinical isolates of A. baumannii. The presence of ISAba1 upstream of the blaOXA-23 gene suggests that the insertion element acts as a promoter for its increased expression.
  
  
  BACKGROUND
  Indian Council of Medical Research, New Delhi, India (ref. no. AMR/TF/54/13ECDHII dated 23 October 2013).
authors.affiliation: Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, 632 004, India.
authors.forename: Saranya
authors.initials: S
authors.lastname: Vijayakumar
authors.affiliation: Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, 632 004, India.
authors.forename: Radha
authors.initials: R
authors.lastname: Gopi
authors.affiliation: Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, 632 004, India.
authors.forename: Priya
authors.initials: P
authors.lastname: Gunasekaran
authors.affiliation: School of Biosciences and Technology, VIT University, Vellore, Tamil Nadu, 632014, India.
authors.forename: Manjurekar
authors.initials: M
authors.lastname: Bharathy
authors.affiliation: Indian Council of Medical Research, New Delhi, India.
authors.forename: Kamini
authors.initials: K
authors.lastname: Walia
authors.affiliation: Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, 632 004, India.
authors.forename: Shalini
authors.initials: S
authors.lastname: Anandan
authors.affiliation: Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, 632 004, India. vbalaji@cmcvellore.ac.in.
authors.forename: Balaji
authors.initials: B
authors.lastname: Veeraraghavan
keywords: Acinetobacter baumannii; Carbapenem resistance; Insertion sequence; Metallo-beta lactamases; Oxacillinases