Direct MALDI-TOF MS and Antimicrobial Susceptibility Testing of Positive Blood Cultures Using the FAST^TM System and FAST-PBC Prep Cartridges—Performance Evaluation in a Clinical Microbiology Laboratory Serving High-Risk Patients

Abstract

Bloodstream infections are a leading cause of morbidity and mortality. The rapid diagnostic testing of positive blood cultures (PBCs) shortens times to effective therapy and the de-escalation of broad-spectrum empiric therapy. This is the first study examining the Qvella FASTTM System for the rapid (~20 min) purification of microorganisms directly from PBCs using BacT/Alert® FA/FAN bottles in the bioMérieux Virtuo instrument. We compared the performance of the FASTTM System Liquid ColonyTM (LC), for immediate downstream ID and phenotypic AST, to standard workflow involving colonies obtained by overnight subculture. The LC yielded a concordant species ID by VITEK MS in 121/138 (87.7%) samples, identifying 32 different Gram-positive and Gram-negative species with 3/123 (2.6%) discordances. Compared to standard workflow, direct AST of the LC using VITEK® 2 yielded 98.4% categorical agreement and 98.0% essential agreement. Very major error, major error, and minor error rates were 1.0%, 0.0%, and 1.8%, respectively, for Gram-negative organisms; and 1.9%, 0.2%, and 1.2%, respectively, for Gram-positive organisms. The median times from positive blood culture flag to results by FASTTM System for ID and AST were 7.8 h and 15.7 h, respectively, versus 22.4 h and 36.6 h for standard workflow, respectively. In conclusion, the FASTTM System provides reliable results for direct ID and AST from PBCs with significantly decreased turnaround times.

Keywords

• bloodstream infection
• rapid diagnostics
• microorganism identification