Type 1 Fimbriae Of Salmonella Typhimurium Mediate Invasion In Vivo In Mice

Members of genus Salmonella are Gram-negative facultative intracellular bacteriabelonging to Enterobacteriaceae, and there are many serotypes. Salmonella is one of themost important pathogens which can cause both people and animal disease.Type 1 fimbriae of Salmonella typhimurium are proteinaceous filaments producedby many members of the family Enterobacteriaceae. It is responsible for the ability ofbacterial adherence and colonization. Furthermore, it is the only fimbriae which canexpress in stationary culture. The previous studyhas proved that type 1 fimbriae can induce thebacterial adherence and colonization to hots cells in vitro.The present study focused on research in vivo and aimed to demonstrate type 1 fimbriaeof Salmonella typhimurium(统一用斜体) will influence the bacterial virulence. The resultswere summarized as follows:1. In order to enhance plasmid stability, aphA-hok-parDE was subcloned into pAZ44which encode the typeâ… fimbriae to obtain pAZ44-h. By comparing the stability ofpAZ44 with pAZ44-h, we confirmed that the plasmid pAZ44 without the stabilizationsystem began to lose plasmid at the 12-24h of culture, while pAZ44-h did not lose theplasmid during the first 10 passages (or 120h of culture). It demonstrated thataphA-hok-parDE apparently enhanced the plasmid stability. This finding laid a goodfoundation for further study of Salmonella typhimurium typeâ… fimbriae.2. The plasmids seperately transformed by electroporation into Salmonellatyphimurium mutant where the genes of invA,lpf1,fim are deleted. The virulence ofrecombinant bacterials was tested at the same time. The results showed that the virulenceof bacteria expressing type 1 fimbriae was decreased shown by LD₅₀ increase of 76-fold.3. Mice were orally immunized with the equal mixture of the bacteria with andwithout expression of Type 1 fimbriae. Three mice were killed at various timepoints of4h, 12h, 24h, 36h, 48h, 72h, 96h, 120h, 144h, 168h, and the blood, mesentery lymphnodes, Peyer' patches, liver, spleen were collected. The tissue was homogenized andthe and the supernatant was plated on MacConkey agar containing different antibiotics.The number of the bacterials grown on the plates were counted.The result shows that thebacterials which cannot express Type 1 fimbriae invaded the body more effective.Taken altogether, the study demonstrated that Type 1 fimbriae of Salmonellatyphimufium decreased bacterial invasion in vivo...