Screening And Effects On The Virulence Genes And Luxs Of Chinese Herbal Extracts Against Streptococcus Suis Biofilm

The microorganisms in biofilms live in a self-produced matrix of hydrated extracellular polymeric substances (EPS) that form their immediate environment. EPS are mainly polysaccharides, proteins, nucleic acids and lipids; they provide the mechanical stability of biofilms, mediate their adhesion to surfaces and form a cohesive, three-dimensional polymer network that interconnects and transiently immobilizes biofilm cells. It has been reported that bacteria living in biofilm exhibit dramatically increased resistance to antibiotics. In fact, Bacteria living in biofilms can be up to10～1000times more resistant to antibacterial compounds than their planktonic cultures of the same strain. There is no doubt that biofilms have enormous implications in the development and treatment of bacterial diseases.Streptococcus suis (S. suis), particularly serotype2, is a major swine pathogen responsible for important economic losses to the porcine industry worldwide. It causes a wide range of life-threatening infections, including meningitis, arthritis, septicaemia, pneumonia, endocarditis and even sudden death. S. suis have a natural tendency to adhere to both eukaryotic cells and abiotic surfaces and form biofilms, which prevent eradication of these organisms by the host immune system or with antimicrobial agents. As such, novel strategies or more effective agents exhibiting an antibiofilm ability with clinical efficacy and safety are of great interest.Therefore, we firstly constructed the S.suis biofilm in vitro. Twenty traditional Chinese herbal were screened based on the colony forming unit method, crystal violet staining and scanning electron microscopy, The results of preliminary screening showed that aqueous of radix et rhizoma rhei, rhizoma coptidis, clove leaf, floslonicerae, radix scutellariae, cortex phellodendri exhibited potent active against S.suis biofilm and the effects were most obvious in radix et rhizoma rhei and rhizoma coptidis. Furthermore, the monomer selected from the rhubarb anthraquinone compounds has intervention negative effect on S.suis biofilm formation. The study demonstrated that emodin in the MIC concentration can reduce the formation of biofilm in a dose dependent manner and this can effectively inhibit S.suis biofilm formation.Real time-PCR was applied to detect the sub-inhibitory concentration in emodin on mRNA expression by S.suis biofilm virulence gene cps, sly, gapdh, gdh, ef, mrp,fbps and the density of sensing system signal molecules LuxS/AI-2protease. Our results indicated that1/2MIC group (0.4882mg-mL-1) compared with biofilm controls can upregulated the expression of mRNA of gdh gene by6.33flod(P<0.01); increase cps gene by2.43flod(P<0.01). On the other hand, it can decreasethe generation of mrp gene by2.53flod(P<0.01), decrease sly gene by5.41flod (P<0.01); derease gapdh gene by4.13flod (P<0.01); decrease ef gene by1.64flod (P<0.05) and decrease fbps gene by3.64flod(P<0.01);in a dose dependent manner. Results indicated that emodin regulated the expression of many virulence genes in S.suis biofilm. Significant decrease of LuxS/AI-2protease was observed (P<0.01) when compared with biofilm controls that indicated an increased concentration of emodin.In conclusion, emodin plays an important role in the regulation of S.suis virulence genes and LuxS protease, It also contributes to the intervention of S.suis biofilm formation in a concentration dependent manner.