Rapid and safe one-step extraction method for the identification of Brucella strains at genus and species level by MALDI-TOF mass spectrometry

PLoS One. 2018 Jun 5;13(6):e0197864. doi: 10.1371/journal.pone.0197864. eCollection 2018.

Abstract

Brucellosis is essentially a disease of domesticated livestock; however, humans can also be infected via the consumption of contaminated meat or dairy products, underlying the need for rapid and accurate identification methods. Procedures for microbiological identification and typing of Brucella spp. are expensive, time-consuming, and must be conducted in biohazard containment facilities to minimize operator risk. The development of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS)-based assay has reduced the processing time while maintaining performance standards. In this study, to improve the identification accuracy and suitability of the MALDI-TOF-based assay for routine diagnosis, we developed a new protein extraction protocol and generated a custom reference database containing Brucella strains representative of the most widespread species. The reference library was then challenged with blind-coded field samples isolated from infected animals. The results indicated that the database could be used to correctly identify 99.5% and 97% of Brucella strains at the genus and species level, respectively, indicating that the performance of the assay was not affected by the different culture conditions used for microbial isolation. Moreover, the inactivated samples were stored and shipped to reference laboratories with no ill effect on protein stability, thus confirming the reliability of our method for routine diagnosis. Finally, we evaluated the epidemiological value of the protocol by comparing the clustering analysis results of Brucella melitensis strains obtained via multiple locus variable-number tandem repeat analysis or MALDI-TOF MS. The results showed that the MALDI-TOF assay could not decipher the true phylogenetic tree, suggesting that the protein profile did not correspond with the genetic evolution of Brucella.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analytic Sample Preparation Methods
  • Brucella / classification*
  • Brucella / genetics
  • Brucella / isolation & purification*
  • Brucella / physiology
  • Databases, Factual
  • Polymerase Chain Reaction
  • Safety*
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*
  • Tandem Repeat Sequences / genetics
  • Time Factors

Grants and funding

Funding for this research was provided by the ANHIWA (Animal Health and Welfare) project Bruepidia Brucellosis in wildlife and domestic animals: development of a direct diagnostic method and assessment of genetic diversity of Brucella melitensis and Brucella suis biovar 2 strains in the EU.