Inhibitor-resistant TEM (IRT) β-lactamases with different substitutions at position 244

Abstract

A novel inhibitor-resistant TEM (IRT) β-lactamase was detected in an Escherichia coli isolate resistant to amoxicillin-clavulanate and susceptible to cephalothin. The substrate and inhibitor profiles of this β-lactamase were similar to those of IRT-1 and IRT-2. The novel IRT's bla gene was sequenced, and the deduced amino acid sequence showed the amino acid replacement Arg for His-244 of the TEM-1 sequence. Substitutions for Arg-244 have been reported in three TEM-1 mutants: IRT-1 (which corresponds to TEM- 31) (Cys), IRT-2/TEM-30 (Ser), and TEM-41 (Thr). We designated this novel β- lactamase, which corresponds to TEM-51, IRT-15.