Chromosome-Encoded Ambler Class A β-Lactamase of Kluyvera georgiana, a Probable Progenitor of a Subgroup of CTX-M Extended-Spectrum β-Lactamases

A chromosome-encoded β-lactamase gene, cloned and expressed in Escherichia coli from Kluyvera georgiana reference strain CUETM 4246-74 (DSM 9408), encoded the extended-spectrum β-lactamase KLUG-1, which shared 99% amino acid identity with the plasmid-mediated β-lactamase CTX-M-8. This work provides further evidence that Kluyvera spp. may be the progenitor(s) of CTX-M-type β-lactamases.