Characterization of two plasmid-encoded cefotaximases found in clinical Escherichia coli isolates: CTX-M-65 and a novel enzyme, CTX-M-87.

Three clinical strains of Escherichia coli (p168, p517 and p667) were collected in 2006 from three hospitals in Anhui Province (China). PCR and DNA sequencing revealed that E. coli p168 carried a novel extended-spectrum beta-lactamase (ESBL), which was designated CTX-M-87. The extended-spectrum beta-lactamase which was carried by E. coli p517 and E. coli p667 was previously named CTX-M-65. The deduced amino acid sequence of CTX-M-87, with pI 9.1, differed from that of CTX-M-14 by the substitutions Ala77-->Val and Pro167-->Leu. Like CTX-M-14, CTX-M-87 had a more potent hydrolytic activity against cefotaxime than against ceftazidime and had high affinity for cefuroxime and cefotaxime. These data show that mutations at position 167 in CTX-M do not always affect catalytic activity and substrate preference.