In vitro activity of ertapenem against carbapenemase-producing enterobacteriaceae. The objective of the present study was to examine the in vitro activity of ertapenem against a wide range of enterobacteria producing carbapenemases including metallo-β-lactamases (MBLs), Ambler class A (KPC), Ambler class B (NDM) and Ambler class D (OXA-48-like) β-lactamases. A total of 116 enterobacteria isolated between 2003 and 2009 in Turkey were collected. Ertapenem was tested against these isolates by disk diffusion methods. The inhibition zone diameters for ertapenem were found to be narrow, indicating resistance among the examined isolates. The inhibition zone diameters for ertapenem were found to be narrow against the majority of the carbapenemase-producing isolates, including KPC-producing isolates. MBL isolates were not inhibited by ertapenem. Ertapenem was found to be a narrow spectrum antibiotic against enterobacteria producing carbapenemases. Therefore, ertapenem was found to be active in vitro against a significant proportion of isolates producing carbapenemases and therefore should be considered a new agent to be used in the treatment of infections caused by these strains. However, further studies are required to establish its efficacy in vivo and clinical utility in infections caused by strains producing carbapenemases.