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 muM(-1) s(-1)) but low values for ceftazidime and aztreonam (<0.02 muM(-1) s(-1)) were observed in hydrolysis assays, indicating resistance to cefotaxime (MIC 64 mug/ml) but susceptibility to ceftazidime (MIC less than or equal to 2 mug/ml).
