|Abstract||Background: Brucellosis is a global zoonosis caused by the bacteria of the genus Brucella a hazard group III pathogen. Typing of Brucella species is of great importance for understanding the epidemiology of the disease and an essential tool for the eradication program and vaccine development. The aim of the present study is to evaluate Matrix-assisted laser desorption ion-ization- time of flight spectrometry (MALDI-TOF MS), a proteomic based as-say, for biotyping B. melitensis in Qatar.
Methodology: A total of sixty three B. melitensis isolated from clinical spec-imens, were biochemically identified by Vitek 2 Compact and serotyped us-ing monospecific Brucella antisera. MALDI-TOF MS Identification was car-ried out against the newly constructed Brucella library. Subsequently, MALDI typing was performed by visual inspection of the generated spectra to determine potential biotype-specific marker peaks. Molecular typing was performed using B. melitensis biotyping PCR kit as a reference method. Results: MALDI-TOF MS identified all the isolates as B. melitensis with a score of >2.3 indicating highly probable species identification. The visual in-spection of the generated spectra revealed six promising marker peaks at m/z 4682, 5028, 5970, 6823, 7356, and 7326. The presence or absence of these marker peaks grouped the isolates into four groups with four distinct marker peak profiles. PCR typing results showed the presence of only two biotypes, B. melitensis biotype 2 (n=32) and B. melitensis biotype 3 (n=31). The mass spectral profiles that share the marker peak at m/z 7356 (n=32) were confirmed as biotype 2 while the mass spectral profiles that share the marker peak at m/z 5970 (n=31) as biotype 3. No B. melitensis biotype 1 was detected in this study. Conclusion: Human brucellosis in Qatar is exclusively caused by B. melitensis with equal distribution of biotype 2 and biotype 3. MALDI-TOF MS was found to be a promising tool to identify and differentiate B. melitensis biotypes 2 and 3. Peak at m/z 7356 was identified as biotype 2-specific marker peak and peak at m/z 5970 as biotype 3-specific.