Optimizing bloodstream infection diagnosis: Implementation of the EUCAST Rapid Antimicrobial Susceptibility Testing (RAST) with automated digital imaging

Bloodstream infections have high mortality, making rapid antimicrobial susceptibility testing (RAST) essential for optimizing empirical therapy. The EUCAST-developed RAST method provides susceptibility results within 4–8 h. The aim of the study is to assess the feasibility of integrating RAST into an automated incubation and digital imaging system (BD Kiestra™), focusing on: (i) digital readability at 4, 6, and 8 h, (ii) categorical agreement (CA), and (iii) detection of ESBL-producing bacteria and MRSA. A prospective study was conducted at Parc Taulí Hospital (September 2023-March 2024). Positive blood cultures were processed following the EUCAST RAST method. Plates were imaged at 4, 6, and 8 h using BD Kiestra™ ReadA browser. Results were compared to the reference microdilution method. CA was calculated, and errors were categorized as very major (VME), major (ME), or minor (mE). ESBL detection was evaluated using cefotaxime and ceftazidime cut-offs and DDST. A total of 133 positive blood cultures were analyzed, including Staphylococcus aureus (39), Escherichia coli (72), Klebsiella pneumoniae (16), and Klebsiella oxytoca (6). Readability was limited at 4 h, but exceeded 98% for Gram-negative bacteria and 85% for S. aureus at 6 h. CA was above 90% for all antibiotics and bacteria, except for E. coli with piperacillin-tazobactam, amoxicillin-clavulanate and ciprofloxacin. ESBL detection surpassed 95% at 6 and 8 h, while MRSA detection was 100% at 8 h. Integrating RAST with digital imaging improves efficiency and enables reliable, remote interpretation of antimicrobial susceptibility, accelerating decision-making in bloodstream infections.