Chromosome-encoded ambler class D beta-lactamase of Shewanella oneidensis as a progenitor of carbapenem-hydrolyzing oxacillinase

A chromosome-encoded beta-lactamase gene from a Shewanella oneidensis reference strain was cloned and expressed in Escherichia coli. It encoded a carbapenem-hydrolyzing Ambler class D beta-lactamase, OXA-54, that shared 92% amino acid identity with the plasmid-encoded carbapenem-hydrolyzing oxacillinase OXA-48 from Klebsiella pneumoniae. This work suggests that Shewanella spp. may produce the progenitor of oxacillinases compromising the efficacy of imipenem in clinically relevant gram-negative pathogens.