Beta-lactamases of Kluyvera ascorbata, probable progenitors of some plasmid-encoded CTX-M types

Abstract

Kluyvera ascorbata produces a beta-lactamase that results in an atypical susceptibility pattern, including low-level resistance to penicillins, cephalothin, and cefuroxime, but this resistance is reversed by clavulanate. Ten nucleotide sequences of the corresponding gene, bla(KLUA), were obtained and were found to have minor variations (96 to 100%). Otherwise, bla(KLUA) was found to be similar (95 to 100%) to some plasmid-encoded CTX-M-type beta-lactamases. Finally, mobilization of bla(KLUA) on a plasmid was found to be mediated probably by a genetic mobile element like ISEcp1.

FIG. 1.

Genetic environment of bla_KLUA-1 gene encoding the β-lactamase produced by K. ascorbata strain CIP 82.95T. The regions surrounding the chromosomal bla_KLUA-1 gene and the sequences adjacent to the plasmidic genes encoding β-lactamases CTX-M-2, CTX-M-4, CTX-M-5, CTX-M-6, CTX-M-7, and Toho-1 (2, 10, 11, 23) were compared. The RTR sequence and tnpA correspond to the right terminal repeat and transposase A, respectively, which are typical of ISEcp1.