Cilastatin does not affect Carba NP test performance for detection of carbapenemase production in Enterobacteriaceae.

The Carba NP test is a simple confirmation method for carbapenemase-producing Enterobacteriaceae (CPE) but reagents have to be freshly prepared as imipenem sodium salt is unstable. We evaluated the Carba NP test performance based on a commercially available 10-fold cheaper drug formulation containing cilastatin against 217 CPE and 78 non-CPE isolates with reduced meropenem susceptibility. Specificity and sensitivity were 100 % and 98.6 %, respectively and 3 false negative results of blaVIM-1-producing Proteus mirabilis were reproducible with the RAPIDEC® Carba NP test. Cilastatin does not disturb test performance provided that the imipenem drug quantity is doubled.