Optimized Use of the MALDI BioTyper System and the FilmArray BCID Panel for Direct Identification of Microbial Pathogens from Positive Blood Cultures

Abstract

Despite the current reliance on blood cultures (BCs), the diagnosis of bloodstream infections (BSIs) can be sped up using new technologies performed directly on positive BC bottles. Two methods (the MALDI BioTyper system and FilmArray blood culture identification [BCID] panel) are potentially applicable. In this study, we performed a large-scale clinical evaluation (1,585 microorganisms from 1,394 BSI episodes) on the combined use of the MALDI BioTyper and FilmArray BCID panel compared to a reference (culture-based) method. As a result, the causative organisms of 97.7% (1,362/1,394) of the BSIs were correctly identified by our MALDI BioTyper and FilmArray BCID-based algorithm. Specifically, 65 (5.3%) out of 1,223 monomicrobial BCs that provided incorrect or invalid identifications with the MALDI BioTyper were accurately detected by the FilmArray BCID panel; additionally, 153 (89.5%) out of 171 polymicrobial BCs achieved complete identification with the FilmArray BCID panel. Conversely, full use of the MALDI BioTyper would have resulted in the identification of only 1 causative organism in 97/171 (56.7%) of the polymicrobial cultures. By applying our diagnostic algorithm, the median time to identification was shortened (19.5 h versus 41.7 h with the reference method; P < 0.001), and the minimized use of the FilmArray BCID panel led to a significant cost savings. Twenty-six out of 31 microorganisms that could not be identified were species/genera not designed to be detected with the FilmArray BCID panel, indicating that subculture was not dispensable for a few of our BSI episodes. In summary, the fast and effective testing of BC bottles is realistically adoptable in the clinical microbiology laboratory workflow, although the usefulness of this testing for the management of BSIs remains to be established.

FIG 1

Bloodstream infection diagnostic workflow using direct (MALDI-TOF MS [MALDI BioTyper system] and/or FilmArray BCID panel) or culture-based (reference) microbial identification methods on positive blood culture (BC) broths. According to the developed algorithm, the FilmArray BCID panel assays were performed on BC broths that revealed multiple morphologies by Gram staining and in all cases for which MALDI BioTyper analysis failed to provide reliable results (i.e., identifications with scores of <1.8, multiple hits in the top 10 matches list with scores ranging from >1.7 to <1.8 that were suggestive of the presence of >1 microbial species, and identifications of organisms, such as S. pneumoniae). MALDI-TOF MS, matrix-assisted laser desorption ionization–time of flight mass spectrometry; BCID, blood culture identification.