Rapid identification of bacteria from positive blood culture bottles by MALDI-TOF MS following short-term incubation on solid media.

Rapid identification of bacteria from blood cultures enables early initiation of appropriate antibiotic treatment in patients with bloodstream infections (BSI). The objective of the present study was to evaluate the use of matrix-associated laser desorption ionization-time of flight (MALDI-TOF) MS after a short incubation on solid media for rapid identification of bacteria from positive blood culture bottles. MALDI-TOF MS was performed after 2.5 and 5.5 h plate incubation of samples from positive blood cultures. Identification scores with values ≥ 1.7 were accepted as successful identification if the results were confirmed by conventional methods. Conventional methods included MALDI-TOF MS, Vitek 2, and diverse biochemical and agglutination tests after overnight culture. In total, 515 positive blood cultures with monomicrobial bacterial growth representing one blood culture per patient were included in the study. There were 229/515 (44.5%) and 286/515 (55.5%) blood culture bottles with Gram-negative bacteria (GNB) and Gram-positive bacteria (GPB), respectively. MALDI-TOF MS following short-term culture could accurately identify 300/515 (58.3%) isolates at 2.5 h, GNB being identified in greater proportion (180/229; 78.6%) than GPB (120/286; 42.0%). In an additional 124/515 bottles (24.1%), identification was successful at 5.5 h, leading to accurate identification of bacteria from 424/515 (82.3%) blood cultures after short-term culture. Interestingly, 11/24 of the isolated anaerobic bacteria could be identified after 5.5 h. The present study demonstrates, in a large number of clinical samples, that MALDI-TOF MS following short-term culture on solid medium is a reliable and rapid method for identification of bacteria from blood culture bottles with monomicrobial bacterial growth.