The Role And Mechanism Of Gb3 In Group B Streptococcus Infection

Group B streptococcus（GBS）,an opportunistic pathogen,is widely colonized in the gastrointestinal tract and urogenital tract.Group B streptococcus（GBS）infection is the leading cause of neonatal meningitis and sepsis,which is a serious threat to the health of pregnant women and newborns.Globotriaosylceramide（Gb3）is a kind of neutral sphingolipid,which exists in the extracellular leaflet of cell membrane and participates in embryonic development,apoptosis,cell adhesion,intercellular coordination,cell differentiation,signal transduction and cancer.At the same time,Gb3 also plays an important role in adhesion to host cells.As a cell surface molecule,it can bind to a variety of bacterial components,such as Shiga toxin and Streptococcus suis Fhb,and plays an important role in the process of many bacterial infections.However,whether and how Gb3 also plays a role in GBS infection remains unknown.To explore the above questions,we first used Gb3 synthetase null mice(A4galt^-/-)to establish a mouse model of Gb3 infection by tail vein injection.To reveal the role of Gb3in group B Streptococcus infection,the bacterial load in blood and organs and the survival of mice were evaluated.The results showed that Gb3 deletion could delay GBS infection and protect mice from GBS infection in the early stage.However,with the extension of infection time and the proliferation of bacteria in the body,this protection gradually weakens and disappears.Then,in order to explore the bacterial ligands that interact with Gb3,magnetic beads were used to couple Gb3 with proteins in vitro,and the bacterial surface protein Rib was identified as a potential ligand for Gb3 by mass spectrometry.A Rib protein-deficient strain（BJCH＿SA4Δrib）was constructed to investigate the role of Rib protein in bacterial infection.We infected mice with the mutant strain and the wild-type strain,respectively,and evaluated the bacterial load in the blood at different time points and in various organs 48h after infection.The mice infected with the mutant strain had a significantly lower bacterial load in blood than those infected with the wild type strain at 5 hours after infection,and a significantly lower bacterial load in kidney and brain than those infected with the wild type strain at 48 hours after infection.In the mouse survival experiment,the survival rate of mice infected with the mutant strain was also significantly higher than that of mice infected with the wild type.After the two strains were mixed,the proportion of wild-type strain was significantly higher than that of mutant strain through the statistics of bacterial load in blood and organs.This suggests that Rib protein,as one of the important virulence factors of group B Streptococcus,plays an important role in the infection of group B Streptococcus and helps GBS escape the clearance of natural immunity.We then used human brain microvascular endothelial cells（h CMEC/D3）to evaluate the changes in adhesion of the two strains.The results showed that the ability of bacteria to adhere to cells was significantly decreased after Rib gene deletion,and Rib protein may play a role in adhering to cells during infection.In conclusion,Gb3 plays a role in GBS infection and Gb3 deletion can delay the progression of bacterial infection.Rib,a group B streptococcal cell surface protein,is a bacterial ligand that interacts with Gb3.As a component of bacterial virulence,Rib participates in the bacterial adhesion process and plays a facilitating role during bacterial infection.