Emergence and Distribution of Plasmids Bearing the bla OXA-51 -Like Gene with an Upstream IS Aba1 in Carbapenem-Resistant Acinetobacter baumannii Isolates in Taiwan

Abstract

ABSTRACT The bla OXA-51 -like gene with an upstream IS Aba1 (IS Aba1 - bla OXA-51 -like gene) was originally found on the chromosomes of carbapenem-resistant or -susceptible Acinetobacter baumannii isolates. However, a plasmid-borne IS Aba1 - bla OXA-51 -like gene has recently been identified in 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 the IS Aba1 - bla OXA-51 -like gene and their significance in A. baumannii . Among the 117 IS Aba1 - bla OXA-51 -like-harboring isolates collected from 10 hospitals in Taiwan, 58 isolates (49.6%) 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 the IS Aba1 - bla OXA-51 -like gene on their chromosomes. Based on the analysis of these four isolates, the plasmid-located IS Aba1 - bla OXA-51 -like gene appeared to be acquired via one-ended transposition (Tn 6080 ). The isolates with a plasmid bearing the IS Aba1 - bla OXA-51 -like gene had higher rates of resistance to imipenem (98% versus 46.6%; P < 0.001) and meropenem (98% versus 69%; P = 0.019) than 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 the IS Aba1 - bla OXA-51 -like gene 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 the IS Aba1 - bla OXA-51 -like gene are widespread in A. baumannii strains in Taiwan.