Abstract: Background: Carbapenem-resistant Acinetobacter baumannii (CRAb) is a major source of nosocomial infections in Spain associated with the production of OXA-58-like or OXA-24/40-like b-lactamase enzymes. We analysed the plasmids carrying the blaOXA-24/40-like gene in CRAb isolates obtained a decade apart. Methods: The presence of b-lactamases was screened for by PCR (metallo-b-lactamases, carbapenem-hydrolysing class D b-lactamases, GES and KPC) in 101 CRAb isolates obtained in two multicentre studies (GEIH/REIPI-Ab2000 and GEIH/REIPI-Ab-2010; n¼493 Acinetobacter spp). We analysed the distribution and characterization of the plasmids carrying the blaOXA-24/40-like gene and sequenced two plasmids, AbATCC223p (2000) and AbATCC329p (2010) from A. baumannii ATCC 17978 transformants. Results: Acquisition of the blaOXA-24/40-like gene was the main mechanism underlying resistance to carbapenems (48.7% in 2000 compared with 51.6% in 2010). This gene was mainly isolated in ST2 A. baumannii strains in both studies, although some novel STs (ST79 and ST80) appeared in 2010. The gene was located in plasmids (8-12 kbp) associated with the repAci2 or repAci2/repGR12 types. The sequences of AbATCC223p (8840 bp) and AbATCC329p (8842 bp) plasmids were similar, particularly regarding the presence of the genes encoding the AbkA/AbkB proteins associated with the toxin/antitoxin system. Moreover, the abkA/abkB gene sequences (.96% identity) were also located in plasmids harbouring the blaOXA-58-like gene. Conclusions: The action of OXA-24/40 and OXA-58 b-lactamase-like enzymes represents the main mechanism underlying resistance to carbapenems in Spain in the last decade. AbkA/AbkB proteins in the toxin/antitoxin system may be involved in the successful dissemination of plasmids carrying the blaOXA-24/40-like gene, and probably also the blaOXA-58-like gene, thus contributing to the plasmid stability.

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