A Plasmid-Borne bla _OXA-58 Gene Confers Imipenem Resistance to Acinetobacter baumannii Isolates from a Lebanese Hospital

Abstract

Conjugation experiments demonstrated that resistance to imipenem could be transferred along with a plasmid containing the carbapenem-hydrolyzing oxacillinase bla OXA-58 gene. The plasmid that we called pABIR was 29,823 bp in size and showed a novel mosaic structure composed of two origins of replication, four insertion sequence (IS) elements, and 28 open reading frames. The bla OXA-58 gene was flanked by IS18 and ISAba3 elements at the 5 and 3 ends, respectively. The production of the carbapenem-hydrolyzing oxacillinase OXA-58 was apparently the only mechanism for carbapenem resistance in A. baumannii isolates causing the outbreak at the Lebanese Hospital.Acinetobacter baumannii is an important opportunistic pathogen responsible for a variety of nosocomial infections, especially in intensive care unit (ICU) patients (11,18). These organisms are frequently resistant to multiple antimicrobial agents including broad-spectrum ␤-lactams, carbapenems, aminoglycosides, and fluoroquinolones (11,18,31). A. baumannii may develop resistance to carbapenems through various mechanisms including decreased permeability because of porin modifications or reduced expression, the overexpression of efflux pumps, and the production of carbapenemases, such as metallo-␤-lactamase or carbapenem-hydrolyzing oxacillinases (CHDLs) (3,(17)(18)(19)(20)(21)(22)(23)(24).The emergence of carbapenem resistance in A. baumannii has been reported worldwide (11,18) and has been correlated in Europe with the acquisition of CHDLs (10,(18)(19)(20)(21)(22)(23). Three main acquired CHDL gene clusters have been identified in A. baumannii, represented by the bla OXA-23 -, bla OXA-24 -, and bla OXA-58 -like genes (13). Plasmid-borne bla OXA-23 and bla OXA-58 genes have been shown to contribute significantly to carbapenem resistance in A. baumannii (3,10,13,18,21,22). In particular, the bla OXA-58 gene has been identified in carbapenem-resistant A. baumannii isolates worldwide (3,13,20,23,30). Recent studies have shown that the flanking insertion sequence (IS) elements ISAba1, ISAba2, ISAba3, and IS18 regulate bla OXA-58 gene expression (22), and ISAba3 possibly regulates its acquisition (19).An outbreak of multidrug-resistant Acinetobacter baumannii was observed between November 2004 and October 2005 in the Saint George University Hospital of Beirut, Beirut, Lebanon. The aim of the present study was to (i) assess the genetic relatedness and the antimicrobial susceptibility of A. baumannii isolates in the hospital, (ii) study the horizontal gene transfer of the carbapenem resistance of the A. baumannii isolates, and (iii) analyze plasmid DNA sequences involved in the acquisition of carbapenem resistance of the A. baumannii isolates. MATERIALS AND METHODS Microbiological methods.A. baumannii isolates were identified as being A. baumannii spp. by using the Vitek 2 automatic system with an ID-GNB card for the identification of gram-negative bacilli according to the manufacturer's instructions (bioMerieux, Marcy-l'Etoile, France). Species identification was conf...

Molecular Epidemiology of Multidrug-Resistant Acinetobacter baumannii in a Tertiary Care Hospital in Naples, Italy, Shows the Emergence of a Novel Epidemic Clone

“…In particular, the emergence of carbapenem resistance has been reported during hospital outbreaks of multidrug-resistant A. baumannii in Italy and southern Europe (4,8,11,13,20,21,(25)(26)(27)(28). Accordingly, the two A. baumannii clones described in the present study showed similar antibiotypes, characterized by resistance to all classes of antimicrobials, including carbapenems, and intermediate resistance to rifampin but susceptibility to colistin.…”

“…PCR analysis for carbapenemase-encoding genes in Acinetobacter spp. (bla IMP , bla VIM , bla SIM , bla OXA-23 -like, bla OXA-24 -like, bla OXA-51 -like, and bla OXA-58 ) was performed as previously described (28). PCR characterization of the bla OXA-58 -surrounding insertion sequence (IS) was performed as described previously (16).…”

“…Etest MBL strips (AB Biodisk, Solna, Sweden) were used to evaluate the presence of metallo-beta-lactamase (MBL) activity according to the manufacturer's procedure. The role of oxacillinase production in carbapenem resistance was assessed by determining carbapenem MICs by microdilution in the presence and absence of 200 mM NaCl, as described previously (28).…”

Molecular Characterization of Acinetobacter Isolates Collected in Intensive Care Units of Six Hospitals in Florence, Italy, during a 3-Year Surveillance Program: a Population Structure Analysis

“…The identity of the sequence of the bla OXA-58 gene from representatives of the A1, A2, and A3 clonal groups is in accordance with horizontal transfer of the gene between strains sharing the same hospital environment. The horizontal transfer of the bla OXA-58-like gene has been already demonstrated (40,41).…”

Horizontal Gene Transfer and Assortative Recombination within the Acinetobacter baumannii Clinical Population Provide Genetic Diversity at the Single carO Gene, Encoding a Major Outer Membrane Protein Channel

“…In these cases, however, the concomitant overproduction of different carbapenem-hydrolyzing enzymes was considered the main factor responsible for carbapenem resistance (21,26). In fact, the overproduction of OXA-type enzymes with the ability to hydrolyze carbapenems is generally considered the principal mechanism of A. baumannii carbapenem resistance (13,35,38,52). The overall observations suggested that CarO could differently contribute to reduced carbapenem susceptibility in different A. baumannii strains and/or play another role(s) in the pathophysiology of this opportunistic pathogen.…”