Microorganisms direct identification from blood culture by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allows a fast and reliable bacterial identification from culture plates. Direct analysis of clinical samples may increase its usefulness in samples in which a fast identification of microorganisms can guide empirical treatment, such as blood cultures (BC). Three hundred and thirty BC, reported as positive by the automated BC incubation device, were processed by conventional methods for BC processing, and by a fast method based on direct MALDI-TOF MS. Three hundred and eighteen of them yield growth on culture plates, and 12 were false positive. The MALDI-TOF MS-based method reported that no peaks were found, or the absence of a reliable identification profile, in all these false positive BC. No mixed cultures were found. Among these 318 BC, we isolated 61 Gram-negatives (GN), 239 Gram-positives (GP) and 18 fungi. Microorganism identifications in GN were coincident with conventional identification, at the species level, in 83.3% of BC and, at the genus level, in 96.6%. In GP, identifications were coincident with conventional identification in 31.8% of BC at the species level, and in 64.8% at the genus level. Fungaemia was not reliably detected by MALDI-TOF. In 18 BC positive for Candida species (eight C. albicans, nine C. parapsilosis and one C. tropicalis), no microorganisms were identified at the species level, and only one (5.6%) was detected at the genus level. The results of the present study show that this fast, MALDI-TOF MS-based method allows bacterial identification directly from presumptively positive BC in a short time (<30 min), with a high accuracy, especially when GN bacteria are involved.

An Evaluation Of Direct Identification Of Pathogens From Blood Cultures By Maldi-Tof Mass Spectrometry

“…With a special set of MALDI Sepsityper is possible to identify bacteria directly from the positive blood culture (17)(18)(19)(20)(21)(22)(23)(24)(25). Most reports describe the blood culture must be grown in automated BACTEC system vials (26,27).…”

Evaluation of MALDI-TOF MS in the microbiology laboratory

“…These methods may be laborious and include several phases such as centrifugation, wash, gel separation and protein extraction. (13) obtained an accurate bacterial identification of 83.3% Gram negative bacteria and 31.8% Gram positive bacteria (28) in comparison with conventional methods. In contrast, Moussaoui et al (24) yielded better results with the accurate identification of 91.1% Gram negative and 89% Gram positive microorganisms through MALDI-TOF MS.…”

“…Besides, the low inoculum of microorganisms present in the samples also hampers the identification of mass spectra. Thus, several research groups have developed and assessed different protocols for the extraction of proteins from microorganisms and removal of substances that may interfere in MALDI-TOF MS analysis (2,13,20,28) . These methods may be laborious and include several phases such as centrifugation, wash, gel separation and protein extraction.…”

Applications of MALDI‐TOF Mass Spectrometry in Clinical Diagnostic Microbiology

“…In one study (Ferreira et al, 2010c), no fungi (0/18) were identified at the species level and only one at the genus level. This poor performance is attributed to the relatively low load of fungi observed in positive blood culture and to the presence of residual blood protein which co-migrates during the MALDI-TOF assay, which impairs the performance of the diagnostic algorithm.…”