Direct identification and susceptibility testing of positive blood cultures: a large-scale evaluation of an ammonium chloride-based in-house workflow.

PURPOSE: Previously, we reported an ammonium chloride-based in-house rapid workflow for direct pathogen identification and antibiotic susceptibility testing from positive blood cultures, eliminating the need for the following overnight subculture. Here, we aimed to assess the workflow’s reliability, accuracy, and potential for integration into routine clinical practice. METHODS: From 2018 to 2022, 1,686 monomicrobial positive blood cultures were processed by the rapid workflow: ammonium chloride lysis/centrifugation/wash followed by MALDI-TOF MS identification and, when indicated, same-day VITEK-2 direct antibiotic susceptibility testing. Results were compared with routine culture-based identification and antibiotic susceptibility testing. RESULTS: The overall agreement between in-house rapid workflow and conventional culture-based methods was 92.59%. Direct antibiotic susceptibility testing using VITEK 2 on 384 gram-negative and 126 gram-positive isolates showed very major, major, and minor error rates of 0.02%, 0.02%, and 1.14% for gram-negative bacteria, and 0.77%, 0.51%, and 1.09% for gram-positive bacteria. In addition, our IH rapid workflow significantly decreased 22.97 h to pathogen identification and 25.3 h to AST results. CONCLUSION: Over five years, our in-house rapid workflow demonstrated reliable performance for pathogen direct identification and antibiotic susceptibility testing from positive blood cultures. The findings suggest that our rapid workflow has the potential to replace the subculturing of positive blood culture isolates to agar plates for definitive identification and antibiotic susceptibility testing. This could be a significant step forward in improving the efficiency and effectiveness of diagnosing and treating bloodstream infections.