Disruption of the bla_OXA-51-like gene by ISAba16 and activation of the bla_OXA-58 gene leading to carbapenem resistance in acinetobacter baumannii Ab244

Objectives: This study examines the mechanism of carbapenem resistance in Acinetobacter baumannii isolate Ab244.Methods: A multiplex PCR for the detection of the bla_OXA-23-like, bla_OXA-40-like, bla_OXA-51-like and bla_OXA-58-like families was performed. MICs of imipenem and meropenem were determined by the agar dilution method. The sequence surrounding the bla_OXA-132 gene was determined by amplification with primer pairs encompassing a part of fxsA and an acetyltransferase gene (GNAT). The sequence upstream of the blaOXA-58 gene was determined by sequencing. SDS-PAGE and carO PCR were performed to check the integrity of the outer membrane proteins. RT-PCRs for the expression of the bla_OXA-132 gene and the bla_OXA-58 gene were performed. Results: Isolate Ab244 harboured bla_OXA-132 belonging to the bla_OXA-51-like gene cluster and a bla_OXA-58 gene. The 4239 bp region between fxsA and GNAT showed an insert of ISAba16 (where IS stands for insertion sequence) after the first 15 nucleotides of the bla_OXA-132 gene, with an 8 bp target site duplication at the 5' and 3' ends of ISAba16. The sequence oriented in the 5′→3′ direction caused insertional inactivation of the bla_OXA-132 gene. The bla_OXA-58 gene was highly expressed by thepromoters provided by an ISAba3-like structure found upstream of the gene. The isolate was resistant to meropenem and had intermediate resistance to imipenem, and was also positive for ISAba1. Conclusions: This is the first report showing ISAba16-mediated inactivation of the bla_OXA-132 gene in strain Ab244. The resistance to carbapenems in strain Ab244 is related to the acquisition of the bla_OXA-58 gene, here governed by an ISAba3-like element.