VirA: a virulence-related gene of Streptococcus suis serotype 2.

Streptococcus suis serotype 2 is an important porcine and human zoonotic pathogen. Few virulence factors have been identified and the pathogenesis of infection is not fully understood. We have identified a novel virulence-related gene, virA, of S. suis 2. To investigate its role in pathogenesis, a virA deletion mutant of S. suis 2 wild-type strain ZY458, 458Deltavir, was constructed using suicide vector pSET4s, and a functionally complemented strain 458Deltavir(pvir) was constructed using shuttle plasmid pAT18 containing the virA gene. All rabbits infected with ZY458 and 458Deltavir(pvir) exhibited body weight loss and developed severe clinical symptoms. All 5 rabbits infected with ZY458, and 4 of 5 infected with 458Deltavir(pvir), died within 6 days of infection. In contrast, all 5 rabbits inoculated with 458Deltavir gained weight normally and none developed any clinical symptoms during the entire course monitored. These results indicate that virA plays an important role in the pathogenicity of S. suis serotype 2. To investigate the virA gene further, we compared and analyzed the sequences of virA from wild-type virulent and avirulent strains. Results showed that functional virA appears to exist only in virulent strains and has been structurally mutated in avirulent strains. In conclusion, virA gene is a novel identified virulence-relate gene. It may play a key role in the evolution and pathogenicity of S. suis serotype 2.