Brucella abortus is a Gram-negative intracellular bacterium that causes infectious abortion in food-producing animals and chronic infection in humans. This study aimed to characterize a B. abortus S19 antigen preparation obtained by Triton X-114 (TX-114) extraction through immunoproteomics to differentiate infected from vaccinated cattle. Three groups of bovine sera were studied: GI, 30 naturally infected cows; GII, 30 S19-vaccinated heifers; and GIII, 30 nonvaccinated seronegative cows. One-dimensional (1D) and two-dimensional electrophoretic profiles of TX-114 hydrophilic phase antigen revealed a broad spectrum of polypeptides (10-79 kDa). 1D immunoblot showed widespread seroreactivity profile in GI compared with restricted profile in GII. Three antigenic components (10, 12, 17 kDa) were recognized exclusively by GI sera, representing potential markers of infection and excluding vaccinal response. The proteomic characterization revealed 56 protein spots, 27 of which were antigenic spots showing differential seroreactivity profile between GI and GII, especially polypeptides <20 kDa that were recognized exclusively by GI. MS/MS analysis identified five B. abortus S19 proteins (Invasion protein B, Sod, Dps, Ndk, and Bfr), which were related with antigenicity in naturally infected cattle. In conclusion, immunoproteomics of this new antigen preparation enabled the characterization of proteins that could be used as tools to develop sensitive and specific immunoassays for serodiagnosis of bovine brucellosis, with emphasis on differentiation between S19 vaccinated and infected cattle.