Variations in IS6 promoters alter the expression of carbapenem resistance in related strains of Acinetobacter baumannii

The aim of this work was to investigate the role of the IS6 family of insertion sequences present upstream of blaOXA-58 in two clonally related carbapenem-resistant Acinetobacter baumannii isolates obtained from paediatric cancer patients in Egypt. To determine their relatedness, the isolates were typed by pulsed-field gel electrophoresis (PFGE), and the intrinsic blaOXA-51-like gene was amplified and sequenced. Minimum inhibitory concentrations (MICs) to imipenem and meropenem was determined according to British Society of Antimicrobial Chemotherapy (BSAC) guidelines. PCR and sequencing of blaOXA-58 and the upstream and downstream regions was performed to determine the genetic environment. The two isolates were positive for the intrinsic blaOXA-64 gene, and the MICs for isolates AB-14298 and AB-P67 were 8 mg/L and 64 mg/L for imipenem and 2 mg/L and 16 mg/L for meropenem, respectively. The blaOXA-58 gene in AB-14298 was flanked by ISAba3 interrupted with IS1006, whereas AB-P67 had ISAba3 interrupted by IS1008, both belonging to the IS6 family of insertion sequences. In conclusion, both IS1006 and IS1008 provided suitable promoter sequences for expression of the downstream blaOXA-58 gene.