Characterization of an extended-spectrum class A β-lactamase from a novel enterobacterial species taxonomically related to Rahnella spp./Ewingella spp.

Abstract

Objectives: To characterize the naturally occurring β-lactamase gene identified from a clinical isolate belonging to a novel enterobacterial species that is closely related to Rahnella spp. and Ewingella spp. Methods: Shotgun cloning and expression in Escherichia coli were performed in order to characterize this resistance determinant. Enzymatic activities were measured by UV spectrophotometry after an ion-exchange chro-matography purification procedure. Results: A chromosomal gene coding for the extended-spectrum β-lactamase (ESBL) SMO-1 was identified from a novel enterobacterial species that is taxonomically related to Rahnella aquatilis and Ewingella americana. The β-lactamase efficiently hydrolysed penicillins and cefotaxime, and shared 75% amino acid identity with the plasmid-mediated β-lactamase SFO-1 from Serratia fonticola, 74% amino acid identity with the plasmid-mediated ESBL CTX-M-2 originating from Kluyvera spp. and 72% amino acid identity with the chromo-somally encoded and intrinsic RAHN-1 from R. aquatilis. Conclusions: We have identified a novel enterobacterial species recovered from a clinical specimen, constituting another potential source of acquired ESBL. The ESBL shared significant similarities with the CTX-M-type enzymes. © The Author 2013. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.