Novel cefotaximase (CTX-M-16) with increased catalytic efficiency due to substitution Asp-240-->Gly.
Three clinical strains (Escherichia coli Rio-6, E. coli Rio-7, and Enterobacter cloacae Rio-9) collected in 1996 and 1999 from hospitals in Rio de Janeiro (Brazil) were resistant to broad-spectrum cephalosporins and gave a positive double-disk synergy test. Two bla(CTX-M) genes encoding beta-lactamases of pl 7.9 and 8.2 were implicated in this resistance: the bla(CTX-M-9) gene observed in E. coli Rio-7 and E. cloacae Rio-9 and a novel CTX-M-encoding gene, designated bla(CTX-M-16), observed in E. coli strain Rio-6. The deduced amino acid sequence of CTX-M-16 differed from CTX-M-9 only by the substitution Asp-240-->Gly. The CTX-M-16-producing E. coli transformant exhibited the same level of resistance to cefotaxime (MIC, 16 microg/ml) but had a higher MIC of ceftazidime (MIC, 8 versus 1 microg/ml) than the CTX-M-9-producing transformant. Enzymatic studies revealed that CTX-M-16 had a 13-fold higher affinity for aztreonam and a 7.5-fold higher k(cat) for ceftazidime than CTX-M-9, thereby showing that the residue in position 240 can modulate the enzymatic properties of CTX-M enzymes. The two bla(CTX-M-9) genes and the bla(CTX-M-16) gene were located on different plasmids, suggesting the presence of mobile elements associated with CTX-M-encoding genes. CTX-M-2 and CTX-M-8 enzymes were found in Brazil in 1996, and two other CTX-M beta-lactamases, CTX-M-9 and CTX-M-16, were subsequently observed. These reports are evidence of the diversity of CTX-M-type extended-spectrum beta-lactamases in Brazil.
Bonnet
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Laboratoire de Bactériologie, Faculté de Médecine, 63001 Clermont-Ferrand Cedex, France. Richard.Bonnet@u-clermont.fr
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Sampaio
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Labia
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D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D001224:Aspartic Acid / Q000235:genetics; D001938:Brazil; D002439:Cefotaxime / Q000494:pharmacology*; D018550:Cephalosporin Resistance / Q000235:genetics*; D002511:Cephalosporins / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000032:analysis; D004352:Drug Resistance, Microbial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D018014:Gene Transfer Techniques; D005998:Glycine / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
D002511:Cephalosporins; D004269:DNA, Bacterial; D001224:Aspartic Acid; C071167:beta-lactamase CTX-2; D001618:beta-Lactamases; D002439:Cefotaxime; D005998:Glycine