Polyclonal spread of bla(OXA-23) and bla(OXA-58) in Acinetobacter baumannii isolates from Argentina.

BACKGROUND: In order to study the enzymatic carbapenem resistance mechanisms in Acinetobacter baumannii isolates from Argentina, we performed molecular characterization on 41 epidemiologically unrelated strains isolated from 1995 to 2006 with diminished susceptibilities to imipenem and meropenem.

METHODOLOGY: Acinetobacter baumannii isolates were identified with the ARDRA technique. The total genomic DNA was used to detect each carbapenem beta-lactamase gene described so far in this species and those insertion sequences usually associated to carbapenem beta-lactamase genes (ISAba1, 2, 3, 4 and IS18) by the PCR technique with specific primers.

RESULTS: 26 out of 41 Acinetobacter baumannii isolates with diminished susceptibilities to carbapenems harboured the bla(OXA-23) gene. The bla(OXA-58) was detected in 13 out of 41 isolates. ISAba1 was always located upstream bla(OXA-23). All isolates containing the bla(OXA-58) gene showed ISAba3 downstream of the carbapenemase, while 4 isolates had a second copy of the ISAba3 upstream of the gene.

CONCLUSION: Enzymatic carbapenem resistance in Acinetobacter baumannii was found in 88% of 41 non-epidemiologically-related strains mediated by the polyclonal spread of the bla(OXA-23) and bla(OXA-58) genes. The genetic structures surrounding the oxacillinase genes found in our bacterial isolates revealed a particular epidemiology in our geographical region. This data suggests the need of local molecular surveillance to help control multirresistance Acinetobacter baumannii infections.