Nevertheless, in the past years it has been
shown that mass spectrometry is a reliable tool for bacterial identification . Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is a fast and easily applied method for bacteria selleck products classification at the species level [23–25]. Mass spectrometry detects and compares individual protein mass peaks of bacterial cells. Samples can either be spotted as native bacteria cells (direct smear), or an additional extraction step can be performed to purify the proteins of the bacteria. Most studies so far were performed with bacterial colonies grown on various solid agar-based media or MALDI-TOF MS was used to identify microorganisms directly in clinical samples such as blood or urine . Only a few studies describe the mass spectrometry
analysis for bacteria grown in liquid media [27, 28]. This can be critical regarding the methodical MALDI-TOF MS sample preparation, and can limit the application for bacteria such as Borrelia or Leptospira, which are commonly grown in nutrient enriched semisolid or liquid media . Recently, it was shown that directly spotted Leptospira samples can be identified at the species level using MALDI-TOF MS . Adavosertib price For some bacterial groups, it has been reported that GDC-0068 research buy extracted samples allow better identification than directly smeared samples [30–32]. This is due to the better quality achieved with extracted samples. In this study we, therefore, evaluated the use of MALDI-TOF MS for extracted Leptospira strains and compared our results with molecular typing methods. The extraction protocol established in this study for Leptospira spp. grown in liquid media ID-8 was used to create a reference spectra database of 28 well-defined Leptospira strains. Based on multiple measurements, the database was evaluated with characterized leptospiral strains and with 16 field isolates.
Statistical analysis with two independently compiled datasets of L. interrogans L. borgpetersenii and L. kirschneri was performed to visualise peak pattern differences of the protein spectra at species level and for certain serovars used in this approach. To confirm the identity for all tested strains, 16S rRNA sequencing and multi locus sequence typing (MLST) analysis was performed and compared to a created dendrogram containing all established reference spectra. In conclusion, MALDI-TOF MS is a rapid and easily applicable method for the characterisation of Leptospira spp. at the species level, and differentiating peaks were identified for a number of the examined strains indicating serovar affiliation. The method can be used as a comparable tool to well-established molecular genetic typing methods like MLST.