CTX-M-14, a Plasmid-Mediated CTX-M Type Extended-Spectrum β-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 μM(−1) s(−1)) but low values for ceftazidime and aztreonam (<0.02 μM(−1) s(−1)) were observed in hydrolysis assays, indicating resistance to cefotaxime (MIC ⩾ 64 μg/ml) but susceptibility to ceftazidime (MIC ⩽ 2 μg/ml).