Variability of chromosomally encoded beta-lactamases from Klebsiella oxytoca.
The beta-lactamase genes of Klebsiella oxytoca were previously divided into two main groups: bla(OXY-1) and bla(OXY-2). The two beta-lactamase groups were each represented by beta-lactamases with four different pIs. In each group, one form of beta-lactamase is more frequent than the others combined. The beta-lactamase gene of each representative beta-lactamase with a different pI that was not yet sequenced (pIs 5.7, 6.8 [OXY-2], 7.1, 8.2, and 8.8 [OXY-1]) was cloned and sequenced. The susceptibility patterns as well as relative rates and kinetic parameters for beta-lactam hydrolysis revealed that OXY-2 enzymes hydrolyzed several of the beta-lactams that were examined (carbenicillin, cephalothin, cefamandole, ceftriaxone, and aztreonam) at a greater rate than the OXY-1 enzymes did. Comparison of K. oxytoca beta-lactamases with plasmid-mediated extended-spectrum beta-lactamases MEN-1 and TOHO-1 implied that the threonine at position 168 present in OXY-2 beta-lactamase instead of the alanine in OXY-1 could be responsible for its modified substrate hydrolysis. In each group, the beta-lactamase with a variant pI differs from the main form of beta-lactamase by one to five amino acid substitutions. The substrate profile and the 50% inhibitory concentrations revealed that all substitutions differing from the main form of beta-lactamase were neutral except one difference in the OXY-1 group. This substitution of an Ala to a Gly at position 237 increases the hydrolysis of some beta-lactams, particularly aztreonam; decreases the hydrolysis of benzylpenicillin, cephaloridine, and cefamandole, and decreases the susceptibility to clavulanic acid (fivefold increase in the 50% inhibitory concentration).
Fournier
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B
Laboratoire et Service d'Infectiologie, Centre Hospitalier de l'Université Laval, Sainte-Foy, Québec, Canada. fournier@helix.mgh.harvard.edu
Roy
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PH
D000595:Amino Acid Sequence; D005798:Genes, Bacterial / Q000235:genetics*; D014644:Genetic Variation; D006868:Hydrolysis; D007709:Klebsiella / Q000201:enzymology*; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013379:Substrate Specificity; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams / Q000378:metabolism*
D065093:beta-Lactamase Inhibitors; D047090:beta-Lactams; D001618:beta-Lactamases