Objectives: The increasing rate of carbapenem resistance in Gram-negative bacteria is a major public health problem and rapid detection is essential for infection management. We evaluated the performances of the MBT STAR^®-Carba IVD assay (Bruker Daltonics) to detect carbapenemase-producing organisms (CPO) from bacterial colonies and directly from positive blood culture bottles with MALDI-TOF MS. Methods: We analyzed 130 strains with a reduced susceptibility to at least one carbapenem including 109 CPO (6 KPC, 27 NDM, 21 VIM, 1 IMP, 41 OXA-48-like, 8 OXA-23, 2 OXA-24/-40, and 2 OXA-58) and 21 non-CPO. The assay on colonies was performed with all 130 strains while the assay on spiked blood cultures was performed with 45 strains. Samples were prepared with the MBT STAR^®-CARBA IVD kit and imipenem hydrolysis by the potential carbapenemase was analyzed with the MBT STAR^®-BL module (Bruker Daltonics) on MALDI-TOF MS. Results: Performed on colonies, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 78), Pseudomonas spp. (n = 19) and Acinetobacter spp. (n = 12). All 21 tested non-CPO remained negative resulting in sensitivity and specificity of 100%. Performed on positive blood cultures, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 23) and Pseudomonas spp. (n = 4) but missed 9/12 carbapenemase-producing Acinetobacter spp. However, a prolonged imipenem-incubation time of the strain pellet improved carbapenemase detection. Non-CPO from positive blood culture bottles remained negative (n = 5) with the assay with the exception of one Klebsiella pneumoniae isolate. Conclusion: The MBT STAR^®-Carba IVD assay is a highly reliable method for the detection of carbapenemase activity in Gram-negative bacteria. However, time-consuming sample preparation steps and reagent costs need to be considered before implementation in a routine clinical microbiology laboratory.

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