Biochemical characterisation of the CTX-M-14 β-lactamase

Cefotaxime-resistant Escherichia coli TUM1121 was isolated from an abscess of an 83-year-old patient. The CTX-M-14 gene was located on a 70 kb plasmid. The enzyme was purified and its activity was analysed. CTX-M-14 was poorly active against ceftazidime and aztreonam. Aztreonam behaved as a competitive inhibitor. Among the tested suicide substrates for class A β-lactamases, sulbactam was a rather good substrate. Tazobactam and clavulanic acid behaved as inactivators. The interactions between clavulanic acid and CTX-M-14 were characterised by progressive inactivation of the β-lactamase. Carbapenems such as imipenem, meropenem or doripenem did not behave as inactivators of CTX-M-14, however very small kcat values were observed. This result shows that CTX-M-14 is able to hydrolyse carbapenems.