Evaluation of the detection performance of the RaST-TAS β-lactamase screening reagent kit based based on the DSTM principle for ESBL production.

Extended-spectrum β-lactamase (ESBL) produced by gram-negative bacilli belonging to the order Enterobacterales confer broad-spectrum antibiotic resistance by hydrolyzing third- and fourth-generation cephalosporins and monobactams. The spread of ESBL-producing organisms drives multidrug resistance and increases healthcare-associated infection rates, underscoring the need for rapid, accurate detection. Conventional methods, including phenotypic tests using β-lactamase inhibitors and PCR-based gene detection, are time-consuming, require specialized equipment, or may not accurately reflect gene expression. In this study, we evaluated the RaST-TAS β-lactamase screening kit, which uses the dynamic sensing test method (DSTM), to assess bacterial morphological changes and determine antimicrobial susceptibility within approximately three hours, for rapid ESBL detection. We analyzed 102 Enterobacterales isolates from blood cultures collected at Kyorin University Hospital between 2022 and 2024 for species identification using Matrix-Assisted Laser Desorption/Ionization - Time-of-Flight Mass Spectrometry followed by ESBL/ AmpC-type β-lactamase(AmpC) gene detection using PCR. RaST-TAS successfully detected 77 out of 80 ESBL-producing isolates, while all AmpC-producing and non-producing isolates tested negative, yielding a sensitivity of 93.9% and a specificity of 100%. Furthermore, the assay time was reduced to approximately three hours compared to 16-24 h for disk diffusion. False negatives were identified in strains co-harboring ESBL and AmpC genes or with low MICs. RaST-TAS provides rapid phenotypic ESBL screening with high specificity within a shortened timeframe compared to conventional phenotypic confirmation tests. While sharing limitations with immunochromatographic assays, its multiplex assessment of β-lactam responses offers complementary functional information.