Chromosome-encoded Ambler class A beta-lactamase of Kluyvera georgiana, a probable progenitor of a subgroup of CTX-M extended-spectrum beta-lactamases

Abstract

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

FIG. 1.

Alignment of the KLUG-1 amino acid sequence with that of CTX-M-8 from C. amalonaticus (3). The numbering is according to the scheme of Ambler et al. (1). Dashes represent identical amino acid residues. The vertical arrow is the putative cleavage site of the leader peptide of the mature β-lactamase KLUG-1. Three structural elements characteristic of class A β-lactamases are boxed in gray (9).

FIG. 2.

Comparison of the surrounding DNA sequences of bla_KLUG-1 and bla_CTX-M-8 of recombinant plasmid pKG-2 and natural plasmid pRio-2, respectively. Boldfaced nucleotides indicate start and stop codons of β-lactamase genes. Vertical bars indicate identical nucleotides, whereas dots represent deleted nucleotides. IS10 IRR refers to the inverted repeat right of an IS10-like element.