A Proof-of-Concept of a 2-Hours Direct Antimicrobial Susceptibility Test from Inoculated Urine Samples

Urinary tract infections (UTIs) are the most frequent infections in hospitalized and outpatient settings, where Escherichia coli is the predominant pathogen. Conventional diagnostic and antimicrobial susceptibility testing (AST) methods are time-consuming, often requiring 48 h, leading to empirical antibiotic therapy and contributing to antimicrobial resistance (AMR). FASTinov^® developed a rapid phenotypic method that enables AST directly from urine samples within two hours using flow cytometry. In this study, 154 inoculated urine samples were analyzed to evaluate the performance of two diagnostic panels: FASTgramneg for Gram-negative bacteria and FASTgrampos for Gram-positive bacteria. Data analysis was performed using bioFAST^® software (version 3.0), providing results in accordance with EUCAST guidelines. The FASTgramneg panel allows detection of resistance mechanisms, including extended-spectrum β-lactamases (ESBLs), and screening of AmpC β-lactamases and carbapenemases; the FASTgrampos panel additionally determines the minimal inhibitory concentration (MIC) of vancomycin for Staphylococcus aureus. Overall agreement with conventional AST methods was 97.5% for Gram-negative bacteria and 95.0% for Gram-positive bacteria. All resistance mechanisms were correctly identified with no false positives. The essential agreement for vancomycin's MIC was 95.2%, with a BIAS of +14.3%. Reproducibility was 99.5% for FASTgramneg and 95.0% for FASTgrampos. These results demonstrate that the FASTinov^® kit significantly reduces turnaround time while maintaining high accuracy, supporting improved UTI management and antimicrobial stewardship.