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Fimbriae and infectivity in Salmonella typhimurium
Abstract:
A genotypically non-fimbriate (Fim-) strain of Salmonella typhimurium and a genotypically fimbriate (Fim+) strain derived from it by spontaneous mutation were compared for pathogenicity in mice. The two strains caused similar numbers of infections and deaths in groups of mice challenged by intraperitoneal inoculation, and nearly similar numbers in groups challenged by inoculation on to the conjunctiva, but the Fim+ strain caused many more infections (plus 26%) and deaths (plus 40%) than the Fim- strain when the inoculation was by mouth. Faecal cultures were made at intervals up to 120 days in the mice surviving after oral or conjunctival challenge and S. typhimurium was isolated more commonly from the animals challenged with the Fim+ strain (906 isolations from 384 animals infected out of 877 challenged) than from those challenged with the Fim- strain (614 isolations from 341 animals infected out of 877 challenged). The greater opportunity for faecal dissemination enjoyed by Fim+ bacteria may account for the preponderance of Fim+ over Fim- strains of S. typhimurium found in mammalian sources.
Insights
Fimbriae enhance Salmonella typhimurium pathogenicity, particularly via oral routes. Fimbriated strains caused more infections and deaths, suggesting fimbriae aid fecal dissemination in mammals.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Immunology
Background:
- Fimbriae are crucial virulence factors in many bacterial pathogens.
- Salmonella typhimurium possesses fimbriae that may influence its host-pathogen interactions.
- Understanding the role of fimbriae in Salmonella pathogenicity is essential for disease control.
Purpose of the Study:
- To compare the pathogenicity of fimbriate (Fim+) and non-fimbriate (Fim-) Salmonella typhimurium strains in a murine model.
- To investigate the influence of fimbriae on infection dynamics and dissemination following different challenge routes.
Main Methods:
- Generation of Fim+ and Fim- Salmonella typhimurium strains through spontaneous mutation.
- Intraperitoneal, conjunctival, and oral challenge of mice with both strains.
- Monitoring infection rates, mortality, and bacterial shedding via fecal cultures up to 120 days.
Main Results:
- Both strains exhibited similar pathogenicity via intraperitoneal and conjunctival routes.
- The Fim+ strain demonstrated significantly increased infections (+26%) and mortality (+40%) following oral challenge.
- S. typhimurium was more frequently isolated from fecal cultures of mice challenged with the Fim+ strain.
Conclusions:
- Fimbriae significantly enhance Salmonella typhimurium pathogenicity, especially following oral ingestion.
- Fimbriae likely facilitate fecal dissemination, contributing to the prevalence of Fim+ strains in mammalian reservoirs.
- These findings highlight the importance of fimbriae in Salmonella epidemiology and host adaptation.