Evaluation of the pathogenesis of meningitis caused by Streptococcus suis sequence type 7 using the infection of BV2 microglial cells.

Streptococcus suis is an important agent of swine and human meningitis. Among several sequence types (STs) characterized within the S. suis strain population, ST7 has emerged only in China and has been reported to be the cause of the human outbreak caused by S. suis in 2005. S. suis ST7 was shown to be derived from S. suis ST1 through a single-nucleotide change in the housekeeping gene thyA. The virulence potential of S. suis ST7 is reported to be higher than that of the worldwide-studied pathogenic S. suis ST1. The pathogenesis of ST1 infection has been partially elucidated, but information on the pathogenesis of ST7 infections remains scarce. To improve our understanding of the mechanisms involved in the development of meningitis caused by ST7, this study compared the microglial inflammatory response induced by ST1 and ST7 strains. The data showed that S. suis ST7 possessed a higher ability to induce pro-inflammatory cytokine production and to activate mitogen-activated protein kinase pathways and several transcription factors. The stimulation of microglial cells by S. suis increased the expression levels of the nucleotide oligomerization domain 2 (Nod2) gene. Finally, the results indicated that signal transducer and activator of transcription 3 (STAT-3) was involved in the development of meningitis induced by S. suis ST7 infection.