Direct antimicrobial susceptibility tests of bacteria and yeasts from positive blood cultures by using serum separator gel tubes and MALDI–TOF MS

Abstract Early and appropriate antimicrobial treatment can effectively reduce the mortality rate caused by bloodstream infections (BSIs) and is critical for favorable patient outcomes. In general, >90% of positive blood cultures will show positive results within 48 h after incubation in the BACTECTM FX system. However, an additional 6–8 h are required to obtain clones of the bacterium and another 10–24 h to obtain antimicrobial susceptibility test (AST) results. In this study, direct ASTs of bacteria and yeasts from positive blood cultures were performed by using serum separator gel tubes and matrix-assisted laser desorption ionization–time of flight mass spectrometry(MALDI-TOF MS). 153 BSI cases were caused by a single pathogen. The coincidence rates of genus and species identification between the direct method (from positive blood cultures) and reference method (from subcultured clones) were 86.9% and 83%, respectively. On average, 98.6% of the direct ASTs in 88 Gram-negative bacteria tested had an accurate result compared to the reference method. In Gram- positive bacteria and yeasts, the accuracy rates were 99.2% and 100%, respectively. MALDI-TOF MS combined with serum separator gel tubes can be used for rapidly identifying and performing ASTs on positive blood cultures.