A two-centre evaluation of RAPIDEC® CARBA NP for carbapenemase detection in Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter spp.

Objectives: We evaluated the RAPIDEC® CARBA NP assay (bioMérieux SA, Marcy-lÉtoile, France), a colorimetric test for rapid detection of carbapenemases, at two sites: Karolinska University Laboratory and PHE's national reference laboratory. Methods: A total of 138 bacterial isolates previously characterized as positive for class A, B and/or D carbapenemase genes and 138 supposed non-carbapenemase producers were tested with RAPIDEC® CARBA NP according to the manufacturer's protocol. Two carbapenemase-producing isolates carried both NDM and OXA-48-like genes. Molecular detection of the expected carbapenemase gene(s) was used as the gold standard, and was performed by conventional and real-time PCR in-house assays. Results: The RAPIDEC® CARBA NP assay detected 135 of 138 carbapenemase producers; one OXA-48-producing Klebsiella pneumoniae and two Acinetobacter baumannii producing OXA-23 or OXA-24 were not detected. Among 'negative' controls, 135 of 138 isolates were negative by RAPIDEC® CARBA NP. The exceptions were one Klebsiella oxytoca, which was later found to produce GES-5 carbapenemase, one Pseudomonas aeruginosa with OprD loss and increased efflux, and one Enterobacter cloacae with impermeability. When numbers were adjusted for the GES-5 producer, the overall sensitivity of the RAPIDEC® CARBA NP test was 97.8% and its specificity was 98.5%. Conclusions: The assay took less than 2.5 h to carry out, was user-friendly and had a high overall performance, making it an attractive option for clinical laboratories.