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Experimental infection of mice with Listeria monocytogenes and L. innocua
Abstract:
Swiss mice were infected with two Listeria strains: L. monocytogenes strain 10401, serovar 4b, and L. innocua strain 390, serovar 6a. Bacteria were inoculated by intravenous, subcutaneous or oral routes, and then enumerated in the spleen. The splenic infection was studied comparatively for these three inoculation routes with both strains. Strain 390 caused a splenic colonization only after intravenous inoculation. For the 10401 strain, the peak of infection appeared on the 3rd day after inoculation; the intravenous route was the most efficient to kill mice, the subcutaneous one the most efficient to obtain a reproductible sublethal infection; the oral route infected regularly only with doses higher than 10(7) bacteria. A splenomegaly appeared only in mice infected with strain 10401. Estimation of Listeria strain pathogenicity depended more on the measure of bacterial count in the spleen on the 3rd day of infection than on LD50. To be able to compare quantitatively the pathogenicity of L. monocytogenes and L. innocua, it seemed impossible to use only one dose of bacteria and to inoculate through one route.
Insights
Comparing Listeria monocytogenes and Listeria innocua infection routes in mice, researchers found that inoculation method and bacterial strain significantly impact splenic colonization and pathogenicity. Strain and route selection are crucial for reproducible Listeria infection studies.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Listeria monocytogenes is a significant human pathogen, while Listeria innocua is considered non-pathogenic.
- Understanding the comparative pathogenicity and infection dynamics of these closely related species is crucial for diagnostics and research.
Purpose of the Study:
- To comparatively analyze the splenic infection and pathogenicity of Listeria monocytogenes and Listeria innocua in Swiss mice.
- To evaluate the influence of different inoculation routes (intravenous, subcutaneous, oral) on infection outcomes for both Listeria strains.
Main Methods:
- Swiss mice were infected with L. monocytogenes (strain 10401) and L. innocua (strain 390) via intravenous, subcutaneous, or oral routes.
- Bacterial counts in the spleen were enumerated at different time points post-infection.
- Pathogenicity was assessed by survival rates, splenic colonization, and observed splenomegaly.
Main Results:
- L. innocua (strain 390) caused splenic colonization only after intravenous inoculation.
- L. monocytogenes (strain 10401) showed peak splenic infection on day 3; intravenous route was most lethal, subcutaneous route yielded reproducible sublethal infections, and oral route required high doses (>10^7 bacteria).
- Splenomegaly was observed only in mice infected with L. monocytogenes (strain 10401).
Conclusions:
- Bacterial count in the spleen on day 3 post-infection is a more reliable indicator of Listeria pathogenicity than LD50.
- Quantitative comparison of L. monocytogenes and L. innocua pathogenicity requires careful selection of bacterial dose and inoculation route, as a single standardized method is insufficient.