The cell envelope subtilisin-like proteinase is a virulence determinant for Streptococcus suis

<p>Abstract</p> <p>Background</p> <p><it>Streptococcus suis </it>is a major swine pathogen and zoonotic agent that mainly causes septicemia, meningitis, and endocarditis. It has recently been suggested that proteinases produced by <it>S. suis </it>(serotype 2) are potential virulence determinants. In the present study, we screened a <it>S. suis </it>mutant library created by the insertion of Tn<it>917 </it>transposon in order to isolate a mutant deficient in a cell surface proteinase. We characterized the gene and assessed the proteinase for its potential as a virulence factor.</p> <p>Results</p> <p>Two mutants (G6G and M3G) possessing a single Tn<it>917 </it>insertion were isolated. The affected gene coded for a protein (SSU0757) that shared a high degree of identity with <it>Streptococccus thermophilus </it>PrtS (95.9%) and, to a lesser extent, with <it>Streptococcus agalactiae </it>CspA (49.5%), which are cell surface serine proteinases. The SSU0757 protein had a calculated molecular mass of 169.6 kDa and contained the catalytic triad characteristic of subtilisin family proteinases: motif I (Asp₂₀₀), motif II (His₂₃₉), and motif III (Ser₅₆₈). SSU0757 also had the Gram-positive cell wall anchoring motif (Leu-Pro-X-Thr-Gly) at the carboxy-terminus, which was followed by a hydrophobic domain. All the <it>S. suis </it>isolates tested, which belonged to different serotypes, possessed the gene encoding the SSU0757 protein. The two mutants devoid of subtilisin-like proteinase activity had longer generation times and were more susceptible to killing by whole blood than the wild-type parent strain P1/7. The virulence of the G6G and M3G mutants was compared to the wild-type strain in the CD1 mouse model. Significant differences in mortality rates were noted between the P1/7 group and the M3G and G6G groups (<it>p </it>< 0.001).</p> <p>Conclusion</p> <p>In summary, we identified a gene coding for a cell surface subtilisin-like serine proteinase that is widely distributed in <it>S. suis</it>. Evidences were brought for the involvement of this proteinase in <it>S. suis </it>virulence.</p

Amoeba Host Model for Evaluation of Streptococcus suis Virulence ▿

The Gram-positive bacterium Streptococcus suis is a major swine pathogen worldwide that causes meningitis, septicemia, and endocarditis. In this study, we demonstrate that the amoeba Dictyostelium discoideum can be a relevant alternative system to study the virulence of S. suis