Improving time-to-result: head-to-head comparison of three rapid AST systems for Gram-negative bacteremia, including the newly developed VITEK REVEAL

ABSTRACT Early antimicrobial susceptibility testing (AST) in Gram-negative (GN) bloodstream infections is critical to guide appropriate therapy. This study evaluated three rapid AST (RAST) systems—VITEK REVEAL, direct-from-blood-culture VITEK 2 (VITEK 2-RAST), and EUCAST disk diffusion (DD-RAST)—using 220 prospectively collected GN-positive blood cultures (GN-PBCs). A total of 18 GN species were tested, including Enterobacterales , Acinetobacter baumannii , and Pseudomonas aeruginosa , against 25 antibiotics, four of which were next-generation β-lactam/β-lactamase inhibitor (BL/BLI) antibiotics. Reference broth microdilution was used for comparison. The VITEK REVEAL assay showed 97.1% essential agreement (EA), −7.7 bias, and 98.3% categorical agreement (CA) across 3,603 organism/antibiotic combinations. The VITEK 2-RAST assay showed 96.2% EA, −10.4 bias, and 98.4% CA across 3,941 combinations. The DD-RAST assay showed 98.2% CA across 2,388 combinations. Among 164 GN-PBCs tested with all three assays, EA rates were 97.5% for VITEK REVEAL and 96.3% for VITEK 2-RAST, with bias values of −7.1 and −6.9, respectively. Across all three assays, the CA rate was ≥98.2%, and very major error (VME) rates were ≤1.8%. Mean time-to-result (TTR) was significantly shorter with VITEK REVEAL (6 h 32 min) compared to VITEK 2-RAST (13 h 51 min) and the fixed 8 h of DD-RAST. In resistant organisms, VITEK REVEAL produced significantly faster results than in susceptible or intermediate ones, including BL/BLI antibiotics. A. baumannii yielded the shortest TTR, with no observed VME. These results support the use of RAST directly on GN-PBCs, with VITEK REVEAL emerging as a particularly promising option for rapid and accurate testing. IMPORTANCE This study is the first to conduct a direct comparison of three rapid antimicrobial susceptibility testing (RAST) systems—VITEK REVEAL, VITEK 2-RAST, and DD-RAST—on a large, prospectively collected cohort of Gram-negative-positive blood cultures (GN-PBCs). The data offer valuable insights for laboratories evaluating RAST implementation, especially in EUCAST-based contexts. Among the systems tested, VITEK REVEAL stood out for its combination of rapid turnaround and high accuracy, including for antibiotic-resistant organisms and β-lactam/β-lactamase inhibitor (BL/BLI) antibiotics. These findings underscore the potential of RAST systems to deliver timely and reliable susceptibility results directly from GN-PBCs, thereby supporting more effective antimicrobial stewardship and clinical decision-making. However, the real-world impact will also depend on how well these systems integrate into routine workflows, as seamless implementation can directly affect time-to-result (TTR)—an essential element in optimizing the management of GN-bloodstream infection (BSI).