Identification Of The Routes Of Streptococcus Suis Breaking Through Human Mucosal Epithelial Cells And The Detection Of Toxicity Strains

Streptococcus suis is an emerging zoonotic agent.The main routes of entry of the organism in humans,in general,were considered to be wound infection and oral infection.S.suis not only can infecte pigs causing a large number of pigs died,but also infecte humans through the consumption of pork infected with S.suis.Infection of Streptococcus suis in humans will lead to permanent hearing loss or suffering from sepsis,meningitis,streptococcal toxic shock syndrome and other illnesses,and even death.In 1968,Denmark reported the first case of Streptococcus suis infection,after which the cases of human infection have been found in Europe,Asia,the America,Australia and New Zealand and other places.Streptococcus suis has caused serious public health problems on a global scale,which has aroused widespread concern among people around the world.However,the current research on the pathogenicity of Streptococcus suis is still very limited.The attachment of bacteria to host cells and their subsequent invasion and spreading are key processes during pathogenesis.Therefore,to study the pathogenic mechanism of pathogens is to study the interaction between pathogens and host cells.To study the epidemic trend of Streptococcus suis and the routes of Streptococcus suis breaking through human mucosal epithelial cells is helpful to prevent and control of Streptococcus suis.In this study,the 16S rRNA gene of 50 isolates was identified by PCR and all the strains were identified as Streptococcus suis.Then 50 isolates of Streptococcus suis were classified by multi-locus sequence typing(MLST)and five different sequence types(STs)were found including twenty-nine ST1,thirteen ST7,four ST242,two ST658 and two ST665.Subsequently,we studied the ability of adhesion,invasion and cytotoxicity of 50 isolates of Streptococcus suis to human epithelial colorectal adenocarcinoma cell line Caco-2 and human laryngeal epithelial cell line Hep-2,and explored the possible routes of Streptococcus suis to break through human mucosal epithelial cells:(1)The Streptococcus suis isolated from human patients could adhere and invade Caco-2 cells and Hep-2 cells.(2)The adhesion of Streptococcus suis to Caco-2 cells was associated with ST.ST7 had the strongest adhesion,while ST1 adhesion was the weakest,the average adhesion index was 3.37 and 0.75 respectively.There was also a significant difference in the ability of adhesion among the strains with the same ST.(3)The invasive ability of 50 strains of Streptococcus suis to Caco-2 cells was correlated with ST.ST7 had the strongest invasive ability,while ST665 had the weakest.Their average invasion index was 43.67 and 1.06,respectively.There was also a significant difference in the ability of invasion among the strains with the same ST.(4)The cytotoxicity of 50 strains of Streptococcus suis to Caco-2 cells was related to ST.The cytotoxic effect of ST658 was the strongest(average 67.35 %),ST242 was the weakest(average of 12.08 %).There was also a significant difference in the cytotoxicity among the strains with the same ST.(5)There were also significant differences in the adhesion,invasion and cytotoxicity of Caco-2 cells and Hep-2 cells in the same strain.The adhesion,invasion and cytotoxicity of most Streptococcus suis to Hep-2 cells was higher than that of Caco-2 cells.(6)Four possible routes of Streptococcus suis to break through human mucosal epithelial cells were proposed:adhered and then directly invaded the epithelial cells;adhered and then released suilysin or other virulence factors to destroy the permeability of host cells and then invaded the epithelial cells;adhered and then through the bypass pathway(translocation)and then invaded epithelial cells;other routes of Streptococcus suis to break through human mucosal epithelial cells.In addition,the pathogenicity island was found to be associated with cytotoxicity.The isolates containing 89 K pathogenicity island were significantly more cytotoxic to host cells than strains without full length of 89 kb.Therefore,based on the 89 K pathogenicity island,the rapid detection method of highly cytotoxicity strains using PCR was established in this study to identify and distinguish isolates that have strong cytotoxicity.