Performance Evaluation of MALDI-TOF MS MBT STAR-BL Versus In-House Carba NP Testing for the Rapid Detection of Carbapenemase Activity in Escherichia coli and Klebsiella pneumoniae Strains

Abstract

There is an urgent need to be able to identify carbapenemase-producing Enterobacterales. In this study we aimed to compare the performance of the MALDI Biotyper Selective Testing of Antibiotic Resistance-βLactamase (MBT STAR-BL) test with the in-house Carba NP test in their ability to rapidly detect carbapenemase production in Escherichia coli and Klebsiella pneumoniae strains. MBT STAR-BL and Carba NP testing were performed in parallel. One hundred sixty-nine isolates in total were tested. K. pneumoniae (n = 139) and E. coli (n = 14) strains with previously characterized carbapenemase types, and non-carbapenemase-producing strains of K. pneumoniae (n = 8) and E. coli (n = 8), were included in the study. When the results of the ertapenem and meropenem hydrolysis assays were evaluated together, MBT STAR-BL correctly identified 151 out of 153 (99%) carbapenemase producers as positive, while giving false-negative results for OXA-48 and OXA-48+NDM-1 producers in two K. pneumoniae isolates. The specificity and sensitivity of MBT STAR-BL were 100% and 98.69%, respectively. For the Carba NP test we confirmed 100% specificity, but sensitivity was 96.7%, although increasing to 100% when using prolonged incubation timing (4 hours). False-negative results were associated with enzymes with low carbapenemase activity, particularly OXA producers, which are common in Enterobacterales.

Keywords: Enterobacterales; MALDI-TOF MS; carbapenemase activity; in-house Carba NP.