An Investigation Of The Pathogenicity Of Salmonella Enterica Serovar Typhi Type IVB Pili

Salmonella Typhi (S. Typhi) is the most important bacteria of Salmonella. It is the only one that is pathogenic exclusively for humans. It infects humans by polluted water and food, and by contacting in everyday life via alimentary tract and causes typhoid or enteric fever which is a serious public health problem in developed countries. There are 600,000 deaths annually in the world . The majority of the deaths are in Asia and African because of economy and living conditions of society. Nearly all S.Typhi infections occur from oral ingestion of bacteria. It moves across the intestinal epithelial cells by alimentary tract. After penetrating it and reaching in the submucosal area, the infectious agents are rapidly internalized and reach a group of antigen-presenting cells which is macrophages. Then the bacteria are phagocytized and some of them are not killed but multipled in it. So S.Typhi is the most important facultative intraceullar pathogen of microorganism.Up to date, people have little known about pathogenesis how the bacteria infected humans. And we have not found a appropriate model of animal or effective methods of genetics to study Salmonella Typhi. And then Salmonella Typhimurium were applied to study the problems of human typhoid fever since it could lead to the same disease in murine. But we could not explain the pathogenesis well by using murine cells or murine models. It caused limitation of studing the pathogenesis of S.Typhi.Recetly, the type IV pili of pathogen are recognized in the field of molecular microbiology. It was identified that the type IV pili as an important virulence factor associated with pathogenicity closely. The gene of pili of S.Typhi is type IVB pili which previously identified in the major pathogenicity island. The type IVB pili contains 11 pil genes forming a pil operon, pilLMNOPQRSTUVr which is found in S.Typhi but not in S.Typhimurium. We found that pilS encoded the main component of the type IVB pili and intestinal immunity against PUS protein would be protective against typhoid fever in humans. A PilS mutant of serover Typhi was much reduced in adhesion to and invasion ofhuman intestinal cells in vitro. But the detailed pathogenesis of type IVB pili of S.Typhi has not been reported in the world.To investigate the pathogenicity of type IVB pili of Salmonella enterica serovar typhi. The cytotoxicity effect of THP-1 cells and mouse peripheral macrophages(M ) were detected by the use of CytoTox96 Non-Radioactive Cytotoxicity Assay after the cells were attacked by Typhi J341, Typhi Aji-e and Typhi pz7S::kmr. Typhi J341 expressed IVB pili, while typhi Aai-e expressed type IVB pili but was inserted with a strong promoter of Tac, and typhi j?z7S::kmr did not express type IVB pili. In order to investigate the invasion of these bacteria, the quantities of pilS gene and rfc gene encoding 0-antigen polymerase of Typhi J341, Typhi A2i-6 and Typhi pilS::kmr were measured after the bacteria entered into human THP-1 cells by the use of fluorescence quantitative PCR (FQ-PCR) method.The results showed that J341, Typhi Aii-e induced stronger cytotoxicity effects to THP-1 cells than that of Typhi /w7S::kmr did(the ratio of bacteria/cell is 24:1, 12:1, 4:1, 2:1). And there were more J341, Typhi A2i-e bacteria entrance into human THP-1 cells than that of Typhi /?z7S::kmr through FQ-PCR analysis.The conclusions: Type IVB pili of Salmonella enterica serovar typhi are important for the cytotoxicity and invasion of the bacteria. Type IVB pili of Salmonella typhi are pathogenicity to the human cells, but may not pathogenicity to the murine cells. However there were no remarkable differences of cytotoxicity effects to mouse peripheral M by these strains. At the same time the invasion of the S.Typhi to the infected cells was correlated to its quantity which may be correlated to the expression of the receptor of the type IVB pili. The detailed pathogenesis need studing more.The research proved pathogenesis of Type IVB pili of Salmonella typhi from cell level to molecular level by the view...