MALDI-TOF Mass Spectrometry analysis first time applied to the identification of the pathogenic and non pathogenic spirochetes (Brachyspira spp. and Leptospira spp.) and benefits of database extension

Objectives: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) recently emerged as a first-line method for the accurate identification of bacteria, but to date no application was evaluated for Brachyspira spp. and few data are available for Leptospira spp. We investigated the potential of MALDI-TOF MS for the rapid identification of isolates of these spirochetes. Methods: In this study, we applied MALDI-TOF MS on human and animal Brachyspira and Leptospira reference strains in order to look for usability and benefits of supplementing the existing database MALDI Biotyper (Bruker Daltonics) and successively we tested additional strains belonging to a well characterized collection to provide evidence for the usefulness of MALDI-TOF MS for the rapid, cheap and reliable spirochaetal identification. Results: Each Brachyspira and Leptospira reference strain yielded a protein profile including unique peaks, so that each strain yielded a unique profile. All the obtained protein profiles were found to be reproducible over a second, independent experiment and no differences were observed when strains were from different lots of media. All reference strains profiles were deposited in a database to be used for further blind identification of additional spirochetal isolates from our collection (at present only for Brachyspira strains). Each strain yielded an identifiable protein profile with an identification score value >2.0. The specific peaks differentiating the Brachyspira and Leptospira species were used for the construction of two separate spectra-based MSP (amin spectrum profile) dendrograms of the reference strains. Conclusion: MALDI-TOF MS is very rapid and only minimal amounts of bacteria are needed, in particular a series of developments including robust and easy-to use software and hardware, a drastically shortening of the time to identification of a positive culture, and even lowering the costs considerably has put the methodology in a central position. Current methods for Brachyspira and Leptospira identification are time-consuming and costly. On the other hand, MALDI-TOF MS makes it possible to identify field isolates with high accuracy and high speed at low cost. In our hands MALDI-TOF MS has proven to be an accurate identification method and a reliable alternative to genetic-based methods for the identification of Brachyspira isolates from both human and animal origin and of Leptospira spp. strains