Applicability of an in-House Saponin-Based Extraction Method in Bruker Biotyper Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry System for Identification of Bacterial and Fungal Species in Positively Flagged Blood Cultures.
We used an in-house saponin-based extraction method to evaluate the performance of the Bruker Biotyper matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) system for the identification of bacteria and fungi in 405 positively flagged blood culture bottles. Results obtained from MALDI-TOF/MS were compared with those obtained using conventional phenotypic identification methods. Of the 405 positively flagged blood culture bottles, 365 showed monomicrobal growth and were correctly identified to the species (72.1%) or genus (89.6%) level using the Bruker Biotyper system. The remaining 40 positively flagged blood culture bottles showed polymicrobial growth. Of them, 82.5% (n= 33) of the isolates were correctly identified to the species level and 92.5% (n= 37) to the genus level using the Bruker Biotyper system. The overall accuracy of identification to the genus level in flagged blood cultures was 89.5% for Gram-positive organisms, 93.5% for Gram-negative pathogens and 71.9% for fungi. Confidence scores were ≥1.500 for 307 (75.8%) bottles, ≥1.700 for 249 (61.5%) bottles and ≥2.000 for 142 (35.1%) bottles. None of the yeast cultures yielded scores ≥1.700. Using an identification-score cutoff of ≥1.500, the MALDI Biotyper correctly identified 99.2% of Gram-positive bacteria, 97.6% of Gram-negative bacteria and 100% of yeast isolates to the genus level and 77.6% of Gram-positive bacteria, 87.1% of Gram-negative bacteria and 100.0% of yeast isolates to the species level. The overall rate of identification using our protocol was 89.9% (364/405) for genus level identification and 73.1% (296/405) for species level identification. Yeast isolates yielded the lowest confidence scores, which compromised the accuracy of identification. Further optimization of the protein extraction procedure in positive blood cultures is needed to improve the rate of identification.
Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan UniversityTaipei, Taiwan; Departments of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan UniversityTaipei, Taiwan.
Jung-Yien
JY
Chien
Departments of Laboratory Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan UniversityTaipei, Taiwan; Departments of Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan UniversityTaipei, Taiwan.
Tai-Fen
TF
Lee
Departments of Laboratory Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University Taipei, Taiwan.
Shin-Hei
SH
Du
Department of Graduate Institute of Biomedical Sciences, Chang Gung UniversityTao-Yuan, Taiwan; Bruker Taiwan Co., Ltd.Taipei, Taiwan.
Shih-Hua
SH
Teng
Department of Internal Medicine, Far Eastern Memorial Hospital Taipei, Taiwan.
Chun-Hsing
CH
Liao
Departments of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University Taipei, Taiwan.
Wang-Hui
WH
Sheng
Departments of Laboratory Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan UniversityTaipei, Taiwan; Departments of Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan UniversityTaipei, Taiwan.
Lee-Jene
LJ
Teng
Departments of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan UniversityTaipei, Taiwan; Departments of Laboratory Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan UniversityTaipei, Taiwan.
Po-Ren
PR
Hsueh
Bruker Biotyper system; MALDI-TOF MS; Vitek MS system; flagged blood cultures; performance
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