A novel chromosome-encoded metallo-β-lactamase (MBL) EBR variant, namely, EBR-5, was identified in a multidrug-resistant Empedobacter stercoris strain SCVM0123 that was isolated from chicken anal swab samples. EBR-5 shared 82.13% amino acid identity with the previously known EBR-1. The expression of EBR-5 in Escherichia coli reduced susceptibility to expanded-spectrum cephalosporins and carbapenems. Compared with blaEBR-1, the recombinant strain harboring blaEBR-5 exhibited higher minimum inhibitory concentrations of piperacillin, cefotaxime, and meropenem. Despite the genetic diversity, EBR-5 and EBR-1 possessed similar kinetic parameters, except for cefepime, cefotaxime, cefoxitin, cephalothin, and meropenem, which were hydrolyzed more by EBR-5. In addition to blaEBR-1, a whole-genome sequencing analysis of SCVM0123 also revealed a plasmid-mediated blaRAA-1 gene. This study underlines the importance of E. stercoris monitoring, as it could be a potential reservoir of these β-lactamase genes. IMPORTANCE Carbapenemases are one of the greatest threats to clinical therapy, as they could confer resistance by hydrolyzing carbapenems and other β-lactam antimicrobials. In this study, we identified a novel metallo-β-lactamase EBR variant, namely, EBR-5, in Empedobacter stercoris. The biochemical properties, substrate hydrolysis abilities, and inhibition profiles of EBR-5 were reported. Through whole-genome sequencing and bioinformatic analyses, we revealed for the first time that the ESBL gene blaRAA-1 was located on a plasmid. This study extends the database of class B metallo-β-lactamases. Meanwhile, E. stercoris could be a major reservoir of blaEBR-5 and blaRAA-1, which have potential to spread to pathogens.
Keywords: E. stercoris; EBR-5; carbapenemase; novel variant.