CTX-M-14, a plasmid-mediated CTX-M type extended-spectrum beta-lactamase isolated from Escherichia coli.

Four Escherichia coli isolates harboring CTX-M-14, with a single Ala231-->Val substitution compared to CTX-M-9, had three different ribotypes. Cefotaxime resistance was plasmid encoded and conjugatively transferable. Three isolates had the same plasmid restriction enzyme digestion profile, suggesting clonal spread of a resistant plasmid. A high k(cat)/K(m) value for cefotaxime (20.3 microM(-1) s(-1)) but low values for ceftazidime and aztreonam (< 0.02 microM(-1) s(-1)) were observed in hydrolysis assays, indicating resistance to cefotaxime (MIC > or = 64 microg/ml) but susceptibility to ceftazidime (MIC < or = 2 microg/ml).