Comparison of in vitro efficacy of ertapenem, imipenem and meropenem by the Enterobacteriaceae strains family

Background.The members of the bacterial Enterobacteriaceae family play an important role in the aetiology of many hospital infections. Some of them are able to produce beta-lactamase, an enzyme which induces the resistance of those bacteria to penicillins, cephalosporins and, in severe infections, to penicillins with beta-lactamase inhibitors. In this situation, the carbapenems become the drugs of choice. The objective of this study was to analyse the in vitro efficacy of three carbapenems: ertapenem, imipenem and meropenem against bacterial species of the Enterobacteriaceae family. Methods. A total of 99 bacterial species (including ten bacterial species producing the ESBL mechanism), isolated between September 2011 and March 2012 from diagnostic material collected from patients of surgical clinics In the department of motoskeletal system infections and the critical care unit, hospitalised in the Military Institute of Medicine in Warsaw, were analysed. The values of MIC 50 and MIC 90 were recorded. Results. All isolated bacterial species were susceptible to meropenem. One strain of Morganella morganii was resistant to imipenem, while one strain of Enterobacter cloaceae and one strain of Klebsiella pneumoniae were resistant to ertapenem. In the Enterobacteriaceae ESBL(-) group, the values of MIC 50 were 0.006 mu g mu L-(1) for ertapenem, 0.19 mu g mu L-(1) for imipenem, and 0.032 mu g mu L-(1) for meropenem, and the MIC 90 values were: 0.25 mu g mu L-(1), 0.5 mu g mu L-(1) and 0.125 mu g mu L-(1), respectively. In the Enterobacteriaceae ESBL(+) group, the values of MIC 50 were 0.38 mu g mu L-(1), 0.25 mu g mu L-(1), 0.064 mu g mu L-(1), and the values of MIC 90 were 0.5 mu g mu L-(1), 0.25 mu g mu L-(1) and 0.125 mu g mu L-(1), respectively. Conclusions. All analysed carbapenems had high in vitro efficacy against both Enterobacteriaceae ESBL(-) and Enterobacteriaceae ESBL(+) bacterial species.