Direct identification of bacteria from charcoal-containing blood culture bottles using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Eur J Clin Microbiol Infect Dis. 2012 Oct;31(10):2843-50. doi: 10.1007/s10096-012-1638-2. Epub 2012 May 26.

Abstract

Several protocols for direct matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) from positive blood cultures are currently used to speed up the diagnostic process of bacteraemia. Identification rates are high and results are accurate for the BACTEC™ system and for charcoal-free bottles. Only a few studies have evaluated protocols for charcoal-containing BacT/ALERT bottles reaching substantially lower identification rates. We established a new protocol for sample preparation from aerobic and anaerobic positive charcoal-containing BacT/ALERT blood culture bottles and measured the protein profiles (n = 167). Then, we integrated this protocol in the routine workflow of our laboratory (n = 212). During the establishment of our protocol, 74.3 % of bacteria were correctly identified to the species level, in 23.4 %, no result and in 2.4 %, a false identification were obtained. Reliable criteria for correct species identification were a score value ≥1.400 and a best match on rank 1-3 of the same species. Identification rates during routine workflow were 77.8 % for correct identification, 20.8 % for not identified samples and 1.4 % for discordant identification. In conclusion, our results indicate that MALDI-TOF MS is possible, even from charcoal-containing blood cultures. Reliable criteria for correct species identification are a score value ≥1.400 and a best match on rank 1-3 of a single species.

MeSH terms

  • Bacteremia / diagnosis*
  • Bacteremia / microbiology
  • Bacteria, Aerobic / classification
  • Bacteria, Aerobic / isolation & purification*
  • Bacteria, Anaerobic / classification
  • Bacteria, Anaerobic / isolation & purification*
  • Bacterial Proteins / analysis
  • Bacteriological Techniques / methods
  • Charcoal
  • Enterobacteriaceae / classification
  • Enterobacteriaceae / isolation & purification
  • Reagent Kits, Diagnostic*
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*
  • Staphylococcus / classification
  • Staphylococcus / isolation & purification
  • Streptococcus / classification
  • Streptococcus / isolation & purification
  • Time Factors

Substances

  • Bacterial Proteins
  • Reagent Kits, Diagnostic
  • Charcoal