The swine pathogen Streptococcus suis is a Gram-positive bacterium which causes infections in pigs, with an impact in animal health and in the livestock industry, and it is also an important zoonotic agent. During the infection process, surface and secreted proteins are essential in the interaction between microorganisms and their hosts. Here, we report a comparative proteomic analysis of the proteins released to the extracellular milieu in six human clinical isolates belonging to the highly prevalent and virulent serotype 2. The total secreted content was precipitated and analyzed by GeLC-MS/MS. In the six strains, 144 proteins assigned to each of the categories of extracellular or surface proteins were identified, as well as 680 predicted cytoplasmic proteins, many of which are putative moonlighting proteins. Of the nine predicted signal peptide-I secreted proteins, seven had relevant antigenic potential when they were analyzed through bioinformatic analysis. This is the first work comparing the exoproteome fraction of several human isolates of this important pathogen.
Keywords: Streptococcus suis; human infection; moonlighting proteins; proteomics; secreted proteins; vaccine candidates; zoonosis.