- CRE: any isolate identified as an Enterobacteriaceae showing a minimum inhibitory concentration (MIC) ≥1 mg/L if using any dilution method and/or ≤22 mm if using a disc-diffusion method for imipenem or meropenem (10 µg disks); all others will be considered carbapenem susceptible (CSE), but meropenem and imipenem susceptible isolates showing resistance to ertapenem will be excluded.