Identification of Bacteria in Blood Culture Broths Using Matrix-Assisted Laser Desorption-Ionization Sepsityper™ and Time of Flight Mass Spectrometry

PLoS One. 2011;6(8):e23285. doi: 10.1371/journal.pone.0023285. Epub 2011 Aug 16.

Abstract

Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a novel method for the direct identification of bacteria from blood culture broths. We evaluate for the first time, the performance of the MALDI Sepsityper™ Kit and MS for the identification of bacteria compared to standard phenotypic methods using the manufacturer's specified bacterial identification criteria (spectral scores ≥1.700-1.999 and ≥2.000 indicated identification to genus and species level, respectively). Five hundred and seven positive blood culture broths were prospectively examined, of which 379 (74.8%; 358 monomicrobial, 21 polymicrobial) were identified by MALDI-TOF MS; 195 (100%) and 132 (67.7%) of 195 gram-positive; and 163 (100%) and 149 (91.4%) of 163 gram-negative organisms from monomicrobial blood cultures were correctly identified to genus and species level, respectively. Spectral scores <1.700 (no identification) were obtained in 128/507 (25.2%) positive blood culture broths, including 31.6% and 32.3% of gram-positive and polymicrobial blood cultures, respectively. Significantly more gram-negative organisms were identified compared to gram-positive organisms at species level (p<0.0001). Five blood cultures were misidentified, but at species level only; including four monomicrobial blood cultures with Streptococcus oralis/mitis that were misidentified as Streptococcus pneumoniae. Positive predictive values for the direct identification of both gram-positive and gram-negative bacteria from monomicrobial blood culture broths to genus level were 100%. A diagnostic algorithm for positive blood culture broths that incorporates gram staining and MALDI-TOF MS should identify the majority of pathogens, particularly to genus level.

MeSH terms

  • Bacteria / classification
  • Bacteria / isolation & purification*
  • Bacteriological Techniques / methods*
  • Gram-Negative Bacteria / classification
  • Gram-Negative Bacteria / isolation & purification
  • Gram-Positive Bacteria / classification
  • Gram-Positive Bacteria / isolation & purification
  • Humans
  • Prospective Studies
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Sepsis / blood
  • Sepsis / diagnosis
  • Sepsis / microbiology*
  • Species Specificity
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*