OXA-carbapenemases present in clinical acinetobacter baumannii-calcoaceticus complex isolates from patients in kurdistan region, Iraq

In addition to intrinsic resistance in Acinetobacter baumannii, many different types of acquired resistance mechanisms have been reported, including the presence of VIM and IMP metallo β-lactamases and also of blaOXA-23-like and blaOXA-58-like enzymes. In the Kurdistan region of Iraq, the multiresistant A. baumannii-calcoaceticus complex is prevalent. We characterized the different mechanisms of resistance present in clinical isolates collected from different wards and different hospitals from the Kurdistan region. One hundred twenty clinical nonduplicate A. baumannii-calcoaceticus complex isolates were collected from four hospitals between January 2012 and October 2013. The identification of the isolates was confirmed by MALDI-TOF.
The susceptibility to different antibiotics was determined by disk diffusion and analyzed in accordance to EUCAST guidelines. By PCR, the presence of blaOXA-51-like, blaOXA-23-like, blaOXA-24-like, and blaOXA-58-like genes was determined as well as the presence of the insertion element ISAba1. Clonal diversity was analyzed by pulsed-field gel electrophoresis (PFGE) using the restriction enzyme ApaI and, in addition, multilocus sequence typing (MLST) was performed on a selected subset of 15 isolates. All 120 A. baumannii isolates harbored blaOXA-51-like genes. One hundred one out of 110 (92%) imipenem (IMP)-resistant A. baumannii-calcoaceticus complex isolates additionally carried the blaOXA-23-like gene and four isolates (3%) were positive for blaOXA-24-like. All 101 blaOXA-23-like-positive isolates had the ISAba1 insertion sequence, 1,600 bp upstream of the blaOXA-23-like gene. The blaOXA-58-like gene was not detected in any of the 110 IMP-resistant strains.
Eight different PFGE clusters were identified and distributed over the different hospitals. MLST analysis performed on a subset of 15 representative isolates revealed the presence of the international clone ST2 (Pasteur). Besides ST2 (Pasteur), also many other STs (Pasteur) were encountered such as ST136, ST94, ST623, ST792, and ST793, all carrying the blaOXA-23 gene. In clinical A. baumannii-calcoaceticus complex isolates from Kurdistan-Iraq, the blaOXA-23 gene in combination with the upstream ISAba1 insertion element is largely responsible for carbapenem resistance. Several small clusters of identical genotypes were found from patients admitted to the same ward and during overlapping time periods, suggesting transmission within the hospital. Identification of source(s) and limiting the transmission of these strains to patients needs to be prioritized.