Clinical Impact of an Integrated MALDI-TOF MS-EUCAST RAST Workflow for Gram-Negative Bloodstream Infections: A Prospective Implementation Study.

OBJECTIVE: To evaluate the clinical impact of an integrated direct MALDI-TOF MS and EUCAST Rapid Antimicrobial Susceptibility Testing (RAST) workflow for Gram-negative bloodstream infections. MATERIALS AND METHODS: This prospective observational implementation study enrolled 100 adults with Gram-negative bloodstream infections between June and November 2025; RAST was completed in 83 patients. Clinical outcomes were compared between 60 intensive care unit (ICU) patients receiving the complete RAST workflow and 64 historical ICU controls managed using conventional microbiological methods. Primary outcomes were antimicrobial treatment appropriateness and time to appropriate therapy, while secondary outcomes included 30-day mortality. RESULTS: Direct MALDI-TOF MS identification showed 100% concordance with conventional identification. RAST reduced mean susceptibility reporting time from 52.1 ± 25.1 to 16.2 ± 6.0 hours (p < 0.001), with 92.9% categorical agreement. Appropriate empirical therapy was more frequent in the RAST group than in controls (51.7% vs. 29.7%, p = 0.013) and increased to 75.0% after RAST-guided treatment revision. Time to appropriate therapy was numerically shorter with RAST (37.8 ± 14.8 vs. 55.5 ± 49.5 hours), without statistical significance (p = 0.410). Thirty-day mortality was similar between groups (56.7% vs. 64.1%, p = 0.399), whereas appropriate antimicrobial therapy was associated with better 30-day survival (log-rank p = 0.002). CONCLUSION: The integrated MALDI-TOF MS-EUCAST RAST workflow substantially shortened susceptibility reporting time and improved treatment appropriateness. Although significant reductions in time to appropriate therapy or mortality were not demonstrated, rapid susceptibility results provided actionable information supporting antimicrobial optimization and stewardship in Gram-negative bloodstream infections.