Comparative analysis of <i>Brucella melitensis</i> whole cell proteomes for diagnosis of human brucellosis

Background & objectives Brucellosis, an occupational zoonosis, poses notable difficulties in diagnosis because of the need for secure facilities and the risk of exposure when using culture-based methods. Conventional serological tests often suffer from cross-reactivity, highlighting the need for more specific diagnostic markers. The purpose of this study was to understand the differences in whole-cell protein expression of Brucella melitensis isolates from patients with acute and chronic brucellosis and to identify immunodominant proteins that could serve as potential diagnostic markers. Methods The study included 16 blood culture-confirmed patients with acute or chronic brucellosis from a cohort of 185 individuals. Clinical isolates of B. melitensis were subjected to two-dimensional gel electrophoresis (2-DE) and PDQuest software analysis to compare proteomic profiles. Differentially expressed proteins were identified using western blotting with infected human serum samples. Further identification of the protein spots was conducted using Matrix-Assisted Laser Desorption/Ionization - Time-of-flight Mass Spectrometry (MALDI-TOF MS). Results The proteomic analysis of B. melitensis identified an average of 249 protein spots. PDQuest software revealed 65 differentially expressed spots, with 17 of these spots successfully identified via MALDI-TOF MS. Western blot assays demonstrated that human sera containing anti-Brucella antibodies reacted with seven immunodominant protein spots. Among these, the outer membrane porin protein (omp25), aldehyde dehydrogenase, and universal stress protein showed potential for differentiating acute from chronic brucellosis. Interpretation & conclusions The findings indicate that omp25, aldehyde dehydrogenase, and universal stress protein are highly specific to B. melitensis infections and could serve as valuable targets for serodiagnosis.