Emergence and distribution of plasmids bearing the blaOXA-51-like gene with an upstream ISAba1 in carbapenem-resistant acinetobacter baumannii isolates in Taiwan

[[abstract]]The ISAba1- blaOXA-51-like gene was originally found on the chromosome of carbapenem resistant or susceptible Acinetobacter baumannii. However, plasmids borne ISAba1- blaOXA-51-like gene has recently been identified in an Acinetobacter genomic species 13TU and several A. baumannii isolates in Taiwan, and all of the isolates are carbapenem resistant. This study aimed to characterize the plasmids bearing ISAba1- blaOXA-51-like and their significance in A. baumannii. Among the 117 ISAba1- blaOXA-51-like harboring isolates collected from 10 hospitals in Taiwan, 58 (49.6%) isolates from 24 clones had the genes located on plasmids that likely originated from a common progenitor. Among the 58 isolates, four had additional copy of ISAba1- blaOXA-51-like on their chromosomes. Based on the analysis of these four isolates, the plasmids located ISAba1- blaOXA-51-like appeared to be acquired via one-ended transposition (Tn6080). The isolates with a plasmid bearing ISAba1- blaOXA-51-like had a higher resistance rate to imipenem (98% vs. 46.6%, p < 0.001) and meropenem (98% vs. 69%, p = 0.019) compared with those with the genes chromosomally encoded, which is most likely due to increased gene dosage provided by the higher copy number of associated plasmids. Transformation with a recombinant plasmid harboring only ISAba1- blaOXA-51-like was enough to confer a high level of carbapenem resistance to A. baumannii, eliminating the possible contribution of other factors on the original plasmids. This study demonstrated that the carbapenem resistance associated plasmids carrying ISAba1- blaOXA-51-like are widespread in A. baumannii in Taiwan