Conversion of OXA-66 into OXA-82 in clinical Acinetobacter baumannii isolates and association with altered carbapenem susceptibility

Abstract

Three clinical Acinetobacter baumannii isolates (A–C) were isolated from three separate patients during an outbreak in a hospital in Krakow, Poland. Isolate A was recovered first and was susceptible to carbapenems, whereas isolates B and C were resistant. The aim of this study was to investigate the differences in carbapenem susceptibility in these outbreak-related isolates. Clonal relatedness was determined using rep-PCR-based DiversiLab. The bla_OXA-51-like genes and their upstream regions were sequenced. Expression of the genes encoding OXA-51-like and the three major porins CarO, OprD-like and 33–36 kDa Omp were investigated by semi-quantitative RT–PCR. Comparison of outer membrane protein (OMP) profiles was performed using SDS–PAGE. ISAba1-bla_OXA-82 was cloned into the shuttle vector pWH1266 and transferred into A. baumannii ATCC 17978. The isolates were identical by rep-PCR and clustered with international clonal lineage 2. Sequencing of bla_OXA-51-like revealed a conversion of OXA-66 (isolate A) into OXA-82 (isolates B and C). bla_OXA-82 was also associated with ISAba1. Expression analysis revealed overexpression of bla_OXA-82. There was no difference in OMP expression between the isolates. ISAba1-bla_OXA-82 conferred carbapenem resistance in ATCC 17978. Carbapenem resistance in outbreak-related isolates was mediated by conversion of OXA-66 into OXA-82 and its subsequent overexpression. This further highlights the genome plasticity of A. baumannii, leading to carbapenem resistance.