Direct identification of pathogens from positive blood cultures by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Abstract

Objective To develop a rapid and accurate technique for pathogens identification from positive blood cultures by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Methods A total of 266 culture-positive blood samples from clinical laboratory in the Second Affiliated Hospital of Soochow University during January to July 2015 were collected. The blood was transferred into separation-gel tubes, and the bacteria were enriched and purified by differential centrifugation. MALDI-TOF MS was applied to identify the bacteria and the results were compared with conventional bacterial culture. Results Among 266 culture-positive blood samples, 260 were monomicrobial cultures and 6 were polymicrobial cultures. Of 260 monomicrobial cultures, 98.8% (257/260) and 96.2% (250/260) of organisms were identified at the genus level and the species level, respectively. Of 140 Gram-negative bacterial isolates, 99.3% (139/140) and 97.9% (137/140) were identified at the genus level and the species level, respectively. Of 120 Gram-positive bacteria isolates, 98.3% (118/120) and 94.2% (113/120) were identified at the genus level and the species level, respectively. None of the 6 polymicrobial cultures were identified. Conclusion MALDI-TOF MS can directly identify the bacteria from positive blood cultures, which provides a rapid and accurate method for the diagnosis of bloodstream infection. Key words: Spectrometry, mass, matrix-assisted laser desorption-ionization; Bacterial infection; Bloodstream infection; Diagnosis