β-Lactamases of Kluyvera ascorbata, Probable Progenitors of Some Plasmid-Encoded CTX-M Types

Kluyvera ascorbata produces a β-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 β-lactamases. Finally, mobilization of bla(KLUA) on a plasmid was found to be mediated probably by a genetic mobile element like ISEcp1.