Molecular detection of OXA carbapenemase genes in multidrug-resistant Acinetobacter baumannii isolates from Iraq and Georgia

Abstract

The aim of this study was to determine the susceptibility to imipenem (IPM) of Acinetobacter baumannii isolates from different countries and to characterise the carbapenemase-encoding genes in IPM-resistant isolates. A total of 12 A. baumannii strains collected in Belgium (n=2), Iraq (n=8) and Georgia (n=2) were included in the study. Identification of the isolates was confirmed using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). Antibiotic susceptibility testing was performed by the disk diffusion method, and Etest was used to determine the IPM minimum inhibitory concentrations (MICs) of resistant isolates. The presence of carbapenemase-encoding genes was investigated by polymerase chain reaction (PCR). All A. baumannii isolates were eventually identified by MALDI-TOF MS with high score values. Amongst the 12 strains, 6 were found to be resistant to IPM (MICs ≥16 μg/mL), comprising clinical isolates from wound infections of soldiers who were injured either during the Iraq war in 2007 (5 isolates) or during the Georgian-Russian war in 2008 (1 isolate from Georgia). All isolates contained ISAba1 and bla(OXA-51-like), but isolates from Iraq contained the bla(OXA-23) gene located on a plasmid whereas the isolate from Georgia contained the bla(OXA-24) gene located on the chromosome. None of the IPM-resistant isolates contained the bla(OXA-58)- or bla(NDM-1)-encoding genes. In conclusion, these results re-emphasise the worldwide dissemination of OXA carbapenemase genes in multidrug-resistant clinical isolates of A. baumannii and, to the best of our knowledge, report the first IPM-resistant A. baumannii strain isolated from a patient during the Georgian-Russian war with the bla(OXA-24) gene located on the chromosome.