Chromosomal beta-lactamase genes of Klebsiella oxytoca are divided into two main groups, (bla)OXY-1 and (bla)OXY-2

The chromosomally encoded beta-lactamase gene (bla(OXY-2)) of the wild-type Klebsiella oxytoca SL911 was cloned and sequenced, Its nucleotide sequence similarity with the previously sequenced K. oxytoca beta-lactamase gene (bla(OXY-1)) (Y. Arakawa, M. Ohta, N. Kido, M. Mori, H. Ito, T. Komatsu, Y. Fujii, and N. Kato, Antimicrob. Agents Chemother, 33:63-70, 1989) is 87.3%, and its amino acid similarity is 89.7%. This group of K. oxytoca beta-lactamases is related to chromosomal beta-lactamases of Citrobacter diversus, Proteus vulgaris, and Yersinia enterocolitica and to the plasmid-mediated extended-spectrum beta-lactamases MEN-1 and Toho-1. By colony hybridization with 86 strains susceptible and resistant to aztreonam, isolated in six countries, K. oxytoca beta-lactamase genes hybridized with either a specific bla(OXY-1) DNA probe (668 bp) or a bla(OXY-2) DNA probe (723 bp). Thus, beta-lactamase genes could be divided into two groups: bla(OXY-1) (-47% of the strains) and bla(OXY-2) (53% of the strains). A study of isoelectric points confirmed the great variability reported in the literature. However, the two beta-lactamase groups were each represented by four different pIs: for OXY-2, 5.2, 5.7, 6.4, and 6.8, with the 5.2 form representing 59% of all OXY-2 enzymes, and for OXY-1, 7.1, 7.5, 8.2, and 8.8, with the 7.5 form representing 88% of all OXY-1 enzymes.