In vitro activities of parenteral β-lactam antimicrobials against TEM-10, TEM-26- and SHV-5-derived extended-spectrum β-lactamases expressed in an isogenic Escherichia coli host

The in vitro activities were determined and time-kill studies of cefepime, imipenem-cilastatin, meropenem and piperacillin-tazobactam were performed against SHV- and TEM-derived extended-spectrum β-lactamases (ESBLs). Sequence-confirmed SHV-5, TEM-10 and TEM-26 β-lactamases were transferred into Escherichia coli C600N by conjugation. Imipenem and meropenem were more active (MIC range 0.0625-0.25 mg/L) than cefepime (MIC range 2-8 mg/L) and piperacillin-tazobactam (MIC range 8-32 mg/L). Regrowth of strains expressing TEM-10 and TEM-26 was noted at all cefepime and piperacillin-tazobactam concentrations studied. Imipenem-cilastatin and meropenem demonstrated rapid, sustained bactericidal activity uninfluenced by the type of ESBL expressed.