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Flagella help Salmonella typhimurium survive within murine macrophages
Abstract:
In this study, we evaluated how flagella enhance the pathogenicity of Salmonella typhimurium in strain C57BL/6J mice. When mice were infected orally with flagellated or nonflagellated S. typhimurium, equivalent numbers of bacteria colonized the gastrointestinal tracts of the animals, but the number of flagellated organisms increased faster once colonization began in the spleens and livers. To evaluate this differential rate of Salmonella growth, the rate of blood clearance, and the kinetics of net multiplication of salmonellae in splenic tissue after intravenous challenge, the two groups of mice were compared. We found that clearance of bacteria from the blood was the same for flagellated or nonflagellated strains. However, the number of flagellated bacteria in the spleen increased logarithmically until the death of the animals, whereas the number of nonflagellated salmonellae increased only slightly. In contrast, both flagellated and nonflagellated strains grew exponentially in the spleens of mice pretreated with silica, a macrophage toxic agent. In an in vitro macrophage assay, flagellated salmonellae survived longer than nonflagellated organisms. These results indicate that flagella either protect S. typhimurium from the intracellular killing mechanisms of murine macrophages or that flagella enhance the ability of S. typhimurium to multiply within murine macrophages.
Insights
Flagella enhance Salmonella typhimurium pathogenicity in mice by promoting bacterial growth in the spleen. This suggests flagella may protect bacteria from macrophage defenses, aiding survival and multiplication.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Flagella are critical virulence factors for many bacterial pathogens.
- Salmonella typhimurium is a significant cause of foodborne illness.
- The role of flagella in Salmonella pathogenesis requires further elucidation.
Purpose of the Study:
- To investigate the role of flagella in Salmonella typhimurium pathogenicity.
- To determine how flagella influence bacterial colonization and growth in vivo.
- To assess the impact of flagella on bacterial survival within host immune cells.
Main Methods:
- Oral and intravenous infection of C57BL/6J mice with flagellated and nonflagellated S. typhimurium strains.
- Quantification of bacterial colonization in the gastrointestinal tract, spleen, and liver.
- Assessment of bacterial blood clearance and splenic multiplication kinetics.
- In vitro macrophage survival assays.
Main Results:
- Flagellated S. typhimurium exhibited enhanced logarithmic growth in the spleen compared to nonflagellated strains.
- Bacterial blood clearance rates were similar for both strains.
- Both flagellated and nonflagellated strains grew in the spleen of silica-treated mice.
- Flagellated S. typhimurium showed increased survival in murine macrophages in vitro.
Conclusions:
- Flagella significantly contribute to Salmonella typhimurium pathogenicity by promoting splenic multiplication.
- Flagella may confer protection against macrophage-mediated bacterial killing.
- Flagella could enhance intracellular survival and proliferation of S. typhimurium within macrophages.