Abstract
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.
Highlights
Carbapenemase-producing organisms (CPO) are a worldwide threat for clinical patient care and public health
We evaluated the commercial MBT STAR R -Carba IVD assay (Bruker Daltonik GmbH, Bremen, Germany) for MALDI-TOF MS carbapenemase detection
A total of 130 Gram-negative isolates, including 89 Enterobacteriaceae (Supplementary Table S1), 29 Pseudomonas spp. and 12 Acinetobacter baumannii complex, intermediate or resistant to at least one carbapenem were selected to evaluate the performances of the MBT STAR R -Carba assay on colonies (Table 1A) These strains included all carbapenem resistant isolates recovered from clinical and screening samples at the microbiology laboratory of the Cliniques universitaires Saint-Luc between January 2015 and March 2018
Summary
Carbapenemase-producing organisms (CPO) are a worldwide threat for clinical patient care and public health. Numerous phenotypic and DNA-based methods have been used in the laboratory aiming at the detection of CPO (Hrabak et al, 2014). Rapid phenotypic methods have been developed such as hydrolysis methods allowing the recognition of all types of carbapenemases with optimal sensitivity and specificity (Dortet et al, 2014a; Tamma and Simner, 2018). These tests include biochemical tests and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) techniques. Several arduous in-house hydrolysis MALDI-TOF MS assays have been described with different sets of antibiotic combinations, buffers, and variable incubation times from 15 min to 4 h (Hrabak et al, 2011; Mirande et al, 2015)
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