A New TEM-Derived Extended-Spectrum β-Lactamase (TEM-91) with an R164C Substitution at the Ω-Loop Confers Ceftazidime Resistance

A new plasmid-mediated TEM-derived extended-spectrum β-lactamase, TEM-91, was identified in a ceftazidime-resistant (MIC, >128 μg per ml) Escherichia coli strain isolated in 1996 in Japan. TEM-91 has three amino acid substitutions, R164C, M184T, and E240K, compared with TEM-1 penicillinase. The isoelectric point (pI), Km, and kcat of TEM-91 for ceftazidime were 5.7, 179 μM, and 29.0 s−1, respectively. The Ki of clavulanic acid for ceftazidime hydrolysis was 30.3 nM.