Rapid MALDI-TOF MS antimicrobial susceptibility testing with the MBT FAST assay.

UNLABELLED: The rise of multidrug-resistant microorganisms highlights the need for rapid antimicrobial susceptibility testing (AST) to guide early and effective therapy. This study evaluated a novel MALDI-TOF MS-based assay (MBT FAST, Bruker, Germany), which employs the direct-on-target microdroplet growth assay (DOT-MGA) for phenotypic AST. A total of 243 Enterobacteriaceae isolates representing diverse species and resistance patterns were tested against a broad panel of antibiotics. Each isolate was incubated in 6-µL microdroplets of cation-adjusted Mueller-Hinton broth, with and without antibiotics at two-fold serial dilutions, at 35°C for 6 h inside a humidity-controlled chamber (MBT FAST Shuttle, Bruker). Broth was removed using a prototype device (MBT FAST Stamp, Bruker), and MALDI-TOF MS measurements were performed with the MALDI Biotyper Sirius system (Bruker). Results were compared with broth microdilution as the standard for determining minimum inhibitory concentrations (MIC). Valid growth control was achieved for 100% of isolates. Essential agreement (EA), defined as MICs within ±1 two-fold dilution step of the standard method, was as follows: amoxicillin/clavulanic acid 96.3%, amikacin 97.5%, aztreonam 95.5%, ceftazidime/avibactam 95.5%, ceftazidime 94.6%, cefepime 92.2%, ciprofloxacin 91.8%, colistin 92.2%, ceftriaxone 95.5%, cefotaxime 94.2%, gentamicin 95.5%, imipenem 91.8%, levofloxacin 97.9%, meropenem 87.2%, meropenem/vaborbactam 94.2%, piperacillin/tazobactam 90.9%, trimethoprim/sulfamethoxazole 90.9%, temocillin 93.3%, and tobramycin 97.5%. The overall EA across all antimicrobials tested reached 96.0%. The research-use-only MBT FAST assay provides reliable AST within 6 h, substantially reducing turnaround time. Building on technology widely implemented in diagnostic laboratories, this approach holds promise for integration into microbiology practice.

IMPORTANCE: Standard antimicrobial susceptibility testing requires prolonged incubation, delaying targeted treatment and de-escalation. This study evaluated MBT FAST, a MALDI-TOF MS-based assay that measures bacterial growth directly on the MALDI target plate in the presence of antibiotics. In a diverse collection of Enterobacteriaceae tested against a panel of 19 antibiotics, the assay provided reliable minimum inhibitory concentration results after 6 h and showed high agreement with standard broth microdilution. Because MALDI-TOF MS instruments are widely used in clinical microbiology laboratories, this approach could make rapid phenotypic susceptibility testing easier to integrate into routine workflows.