blaOXA-23-like and blaTEM rather than blaOXA-51-like contributed to a high level of carbapenem resistance in Acinetobacter baumannii strains from a teaching hospital in Xi’an, China

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Acinetobacter baumannii is one of the major threats in clinical infections due to its antibiotic resistance ability. It shows increasing resistance to carbapenems, mainly due to β-lactamase mediated mechanisms. The aim of this study was to investigate carbapenem resistance (CR) profiles and analyze β-lactamases genes composition of clinical A. baumannii strains from a teaching hospital in Xi’an. The resistance patterns to imipenem and meropenem were checked for 51 clinical A. baumannii strains. The existence of 15 β-lactamases genes was detected by polymerase chain reaction (PCR), and the positive genes were sequenced. The correlation between PCR-positive genes and CR phenotype was analyzed using Chi-square test and contingency coefficient. The expressions of PCR-positive genes were investigated. Forty-five out of 51 strains were resistant to imipenem and meropenem. blaTEM, blaOXA-23-like, and blaOXA-51-like were positive among 15 β-lactamases genes, and TEM-1, OXA-23, and OXA-66/69 were their subtypes. TEM and OXA-23-like only showed up in CR isolates, with the occurrence rate of 91.1% and 97.8%, respectively, whereas OXA-51-like appeared in all strains. ISAba1 was present in the upstream of OXA-23-like, but absent from that of OXA-51-like in our strains. OXA-23-like had highest relationship with CR, followed by TEM, but OXA-51-like had no correlation. This was verified by RT-qPCR that the expression was positive for OXA-23 and TEM-1, but negative for OXA-66/-69. A high rate of CR A. baumannii was detected in this study. Coexistence of TEM, OXA-23-like, and OXA-51-like was the primary resistance profile. The expressions of OXA-23-like and TEM genes were closely related with CR, while OXA-51-like had no contribution to the CR phenotype.

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