Objectives: This study examines the mechanism of carbapenem resistance in Acinetobacter baumannii isolate Ab244.Methods: A multiplex PCR for the detection of the blaOXA-23-like, blaOXA-40-like, blaOXA-51-like and blaOXA-58-like families was performed. MICs of imipenem and meropenem were determined by the agar dilution method. The sequence surrounding the blaOXA-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 blaOXA-132 gene and the blaOXA-58 gene were performed. Results: Isolate Ab244 harboured blaOXA-132 belonging to the blaOXA-51-like gene cluster and a blaOXA-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 blaOXA-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 blaOXA-132 gene. The blaOXA-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 blaOXA-132 gene in strain Ab244. The resistance to carbapenems in strain Ab244 is related to the acquisition of the blaOXA-58 gene, here governed by an ISAba3-like element.
Bibliographical noteFunding Information:
We are grateful to the University of Edinburgh for the Overseas Research Scholarship and the College of Medicine and Veterinary Medicine bursary to B. S. L. We are grateful to the Medical Research Council for grant number RA0119, which funded part of this work.