Guideline for phenotypic screening and confirmation of carbapenemases in Enterobacteriaceae

Adequate detection of carbapenemase-producing Enterobacteriaceae is crucial for infection control measures and appropriate choice of antimicrobial therapy. This guideline aims to improve the detection of carbapenemase-producing Enterobacteriaceae in the routine setting of clinical microbiology laboratories. Detection of carbapenemases in Enterobacteriaceae includes a screening step followed by a genotypic and optional phenotypic confirmatory step. For all Enterobacteriaceae, the meropenem screening breakpoint to detect carbapenemases is set at ≥0.5 mg/L or a zone diameter of ≤23 mm (10 μg disk loading). For Escherichia coli, Klebsiella spp., Salmonella spp., Enterobacter spp. and Citrobacter spp., the imipenem screening breakpoint is set at ≥2 mg/L or a zone diameter ≤21 mm. Ertapenem is not advised as an indicator carbapenem as it has a lower specificity compared with imipenem and meropenem. On the first isolate from a patient with a positive carbapenemase screen test, a polymerase chain reaction (PCR)-based test should be performed to detect carbapenemase genes. However, if genotypic confirmation is not immediately available, phenotypic confirmation tests should be performed to avoid delayed reporting of carbapenemase-producers to the clinic. Recommended phenotypic confirmation tests are the modified Hodge test as well as carbapenemase inhibition tests with boronic acid for Ambler class A carbapenemases and with ethylene diamine tetra-acetic acid (EDTA) or dipicolinic acid for metallo-carbapenemases.