Objectives: Carbapenem resistance in Acinetobacter spp. is increasing and is primarily associated with the expression of OXA-type β-lactamases. However, the role of intrinsic OXA-type β-lactamases in the carbapenem resistance of Acinetobacter spp. has not been fully elucidated. The aim of this study was thus to understand this issue.
Methods: We applied bioinformatic screening of putative blaOXA genes against available genome sequences. The putative blaOXA genes were cloned into pKFAb and expressed in Escherichia coli and Acinetobacter baumannii to determine their antibiotic susceptibility. blaOXA genes were knocked out in their native hosts using pEX18Gm.
Results: Five novel groups of carbapenem-hydrolysing OXA-type β-lactamases were identified in Acinetobacter rudis, Acinetobacter bohemicus, Acinetobacter tandoii, Acinetobacter gyllenbergii, Acinetobacter proteolyticus, Acinetobacter dispersus, Acinetobacter colistiniresistens and Acinetobacter guillouiae. The five OXA groups clustered into five highly supported monophyletic clades and are distinct from known OXA-type carbapenemases in the phylogenetic tree. Most of them conferred resistance to imipenem, meropenem, ertapenem, amoxicillin and ampicillin in E. coli and A. baumannii. The conserved location and prevalence of the blaOXA genes among the species suggest they are intrinsic. The blaOXA genes in A. rudis, A. guillouiae and A. gyllenbergii were knocked out separately and the blaOXA-665-deficient A. rudis and blaOXA-274-deficient A. guillouiae exhibited increased susceptibility to imipenem, meropenem, amoxicillin and ampicillin.
Conclusions: Five novel intrinsic OXA groups were identified in the genus Acinetobacter and most of them can hydrolyse carbapenems. This study furthers our understanding of the wide distribution of carbapenem-hydrolysing OXA-type β-lactamases in Acinetobacter spp.