Streptococcus suis (S. suis) is a swine pathogen and also a zoonotic agent. In this study, the effects of subinhibitory concentrations (sub-MICs) of emodin on biofilm formation by S. suis ATCC700794 were evaluated. As quantified by crystal violet staining, biofilm formation by S. suis ATCC700794 was dose-dependently decreased after growth with 1/2 MIC, 1/4 MIC, or 1/8 MIC of emodin. By scanning electron microscopy, the structural architecture of the S. suis ATCC700794 biofilms was examined following growth in culture medium supplemented with 1/2 MIC, 1/4 MIC, 1/8 MIC, or 1/16 MIC of emodin. Scanning electron microscopy analysis revealed the potential effect of emodin on biofilm formation by S. suis ATCC700794. The expression of luxS gene and virulence genes in S. suis ATCC700794 was investigated by quantitative RT-PCR. It was found that sub-MICs of emodin significantly decreased the expression of gapdh, sly, fbps, ef, and luxS. However, it was found that sub-MICs of emodin significantly increased the expression of cps2J, mrp, and gdh. These findings showed that sub-MICs of emodin could cause the difference in the expression level of the virulence genes.
Keywords: Biofilm formation; Emodin; Streptococcus suis; Virulence factors.