Characterization of a Chromosomally Encoded Extended-Spectrum Class A β-Lactamase from Kluyvera cryocrescens

A chromosomally located β-lactamase gene, cloned and expressed in Escherichia coli from a reference strain of the enterobacterial species Kluyvera cryocrescens, encoded a clavulanic acid-inhibited Ambler class A enzyme, KLUC-1, with a pI value of 7.4. KLUC-1 shared 86% amino acid identity with a subgroup of plasmid-mediated CTX-M-type extended-spectrum β-lactamases (CTX-M-1, -3, -10, -11, and -12), the most closely related enzymes, and 77% amino acid identity with KLUA-1 from Kluyvera ascorbata. The substrate profile of KLUC-1 corresponded to that of CTX-M-type enzymes.