Rapid phenotypic antimicrobial susceptibility testing of Gram-negative bloodstream isolates: clinical evaluation of...

Bloodstream infections (BSIs) and sepsis require rapid initiation of appropriate antimicrobial therapy; however, conventional antimicrobial susceptibility testing (AST) methods are time-consuming and may delay targeted treatment. Rapid phenotypic AST performed directly from positive blood cultures may reduce time to effective therapy and support antimicrobial stewardship.

The analytical performance and turnaround time (TAT) and the time-to-result (TTR) of the LifeScale AST system were evaluated using monomicrobial Gram-negative organisms from positive blood cultures. A total of 156 adult blood culture isolates were tested in parallel using the LifeScale system and the standard-of-care (SoC) MicroScan WalkAway system. Performance was assessed across 14 antimicrobial agents using Essential agreement (EA), adjusted Categorical agreement (CA), and categorical error rates in accordance with Clinical and Laboratory Standards Institute (CLSI) 2025 breakpoints. Discrepant results were resolved by broth microdilution (BMD).

Across 1,360 organism-antimicrobial combinations, the LifeScale AST system demonstrated an overall EA of 97.72% and an adjusted CA of 95.81% following discrepancy resolution. No very major errors remained after adjudication; the final major and minor error rates were 0.37% and 3.90%, respectively. Median TAT was 8.6 h for the LifeScale system compared with 48.1 h for the SoC method, corresponding to a median reduction of 39.5 h and an approximately 80% decrease in TAT; the mean TTR was 4.2 h.

The LifeScale AST system demonstrated high analytical agreement with the SoC method while substantially reducing TAT for AST testing of Gram-negative bloodstream infection isolates. Rapid availability of reliable phenotypic susceptibility results directly from positive blood cultures may enable earlier optimization of antimicrobial therapy and support antimicrobial stewardship, particularly in the management of sepsis.