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Inoculum composition and Salmonella pathogenicity island 1 regulate M-cell invasion and epithelial destruction by
M A Clark1, B H Hirst, M A Jepson
1Department of Physiological Sciences, Medical School, University of Newcastle upon Tyne, United Kingdom. Ann.Clark@newcastle.ac.uk
Abstract:
In the mouse model of Salmonella typhimurium infection, the specialized antigen-sampling intestinal M cells are the primary route of Salmonella invasion during the early stages of infection. Under certain experimental conditions, M-cell invasion is accompanied by M-cell destruction and loss of adjacent regions of the follicle-associated epithelium (FAE), although the conditions responsible for expression of the cytotoxic phenotype in a proportion of previous studies have not been defined. In the present study, we have demonstrated that the cytotoxic effect exerted by wild-type S. typhimurium on mouse Peyer's patch FAE is dependent on the inoculum composition. We have also demonstrated that the extent of FAE destruction correlates with the extent of M-cell invasion. Bacteria inoculated in Luria-Bertani (LB) broth induce extensive FAE loss and exhibit efficient M-cell invasion, whereas bacteria inoculated in phosphate-buffered saline fail to induce significant FAE disruption and invade M cells at significantly lower levels. Similarly, inoculation in LB significantly enhances invasion of Madin-Darby canine kidney cells by wild-type S. typhimurium. Mutants defective for expression of invA, a component of Salmonella pathogenicity island 1 which is vital for efficient invasion of cultured cells, fail to induce FAE destruction and, when inoculated in LB, are attenuated for M-cell invasion. Variation in inv gene expression is, therefore, one possible mechanism by which inoculate composition may regulate the virulence of wild-type S. typhimurium. Our findings suggest that the composition of the gut luminal contents may be critical in determining the outcome of naturally acquired Salmonella infections and that both vaccine formulation and dietary status of vaccine recipients may significantly affect the efficacy and safety of live Salmonella oral vaccine delivery systems.
Insights
Salmonella typhimurium invasion and gut tissue damage depend on the bacterial growth medium. Luria-Bertani broth enhances Salmonella invasion and follicle-associated epithelium loss, unlike phosphate-buffered saline.
Area of Science:
- Microbiology
- Immunology
- Gastroenterology
Background:
- Intestinal M cells are key entry points for Salmonella typhimurium.
- Salmonella invasion can cause M cell destruction and follicle-associated epithelium (FAE) loss.
- Conditions triggering Salmonella's cytotoxic effects on FAE are not fully understood.
Purpose of the Study:
- To investigate how inoculum composition affects Salmonella typhimurium's cytotoxic effects on mouse Peyer's patch FAE.
- To determine the correlation between FAE destruction and M cell invasion.
- To explore the role of invA gene expression in Salmonella virulence.
Main Methods:
- Comparing Salmonella typhimurium virulence in mice using different inoculation media (Luria-Bertani broth vs. phosphate-buffered saline).
- Assessing M cell invasion and FAE destruction levels.
- Evaluating invasion of Madin-Darby canine kidney cells.
- Testing Salmonella mutants defective in invA expression.
Main Results:
- Bacteria in Luria-Bertani broth induced significant FAE loss and enhanced M cell invasion compared to phosphate-buffered saline.
- FAE destruction extent correlated with M cell invasion levels.
- invA mutants showed reduced FAE destruction and attenuated M cell invasion, even in Luria-Bertani broth.
Conclusions:
- Inoculum composition critically influences Salmonella typhimurium virulence and FAE damage.
- invA gene expression is a key factor in Salmonella-induced FAE destruction and M cell invasion.
- Gut luminal contents, vaccine formulation, and host diet may impact live Salmonella oral vaccine efficacy and safety.