Detection of extended-spectrum β-lactamases producing Enterobacteriaceae using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry based MBT STAR-BL software module with β-lactamase inhibition assay depends on the bacterial strains.

Rapid and sensitive detection of extended-spectrum β-lactamases (ESBLs) is essential for infection control and antimicrobial treatment. Recently, a matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based MBT STAR-BL software module has been used for detecting β-lactamase activity; however, this system cannot differentiate ESBL producing bacteria from other third-generation cephalosporin-resistant strains. In this study, we utilized a MALDI-TOF MS-based MBT STAR-BL method to identify ESBL activity with β-lactamase inhibitors. A cefotaxime (CTX) hydrolysis assay, β-lactamase inhibition, clavulanic acid (CVA), and sulbactam (SBT) were used for detecting ESBL producers with the MBT STAR-BL software module. This software module automatically calculated the logRQ values in each assay. logRQ is the logarithm of the ratio of the summed hydrolyzed peak intensities to the summed non-hydrolyzed peak intensities and measured the efficiency of antibiotic hydrolysis. We divided the logRQ level of the β-lactamase inhibition assay by the logRQ value in the CTX hydrolysis assay, and we used this logRQ ratio as a measure of β-lactamase inhibition efficiency. We assessed the logRQ ratio calculated by this novel method for detecting ESBL producers in 132 Enterobacteriaceae. We performed the MALDI-TOF MS-based MBT STAR-BL approach with β-lactamase inhibitors for detecting ESBL producers and showed that the results of the inhibition assay with β-lactamase inhibitors depended on types of bacterial species. Furthermore, we improved elapsed times and accuracy in MBT STAR-BL methods by using proper β-lactamase inhibitors against specific bacterial strains to compare with the conventional standard lab method. The results suggest that the target bacterial species and β-lactamase inhibitors used were important for the utility of the MALDI-TOF MS-based MBT STAR-BL software module.