Mouse lung infection model to assess Rhodococcus equi virulence and vaccine protection
Patricia González-Iglesias1, Mariela Scortti2, Iain MacArthur1
1Microbial Pathogenesis Unit, School of Biomedical Sciences and The Roslin Institute, University of Edinburgh, Edinburgh, UK.
Abstract:
The pathogenic actinomycete Rhodococcus equi causes severe purulent lung infections in foals and immunocompromised people. Although relatively unsusceptible to R. equi, mice are widely used for in vivo studies with this pathogen. The most commonly employed mouse model is based on systemic (intravenous) infection and determination of R. equi burdens in spleen and liver. Here, we investigated the murine lung for experimental infection studies with R. equi. Using a 10(7)CFU intranasal challenge in BALB/c mice, virulent R. equi consistently survived in quantifiable numbers up to 10 days in the lungs whereas virulence-deficient R. equi bacteria were rapidly cleared. An internally controlled virulence assay was developed in which the test R. equi strains are co-inoculated and monitored in the same mouse. Isogenic R. equi bacteria lacking either the plasmid vapA gene or the entire virulence plasmid were compared using this competitive assay. Both strains showed no significant differences in in vivo fitness in the lung, indicating that the single loss of the virulence factor VapA was sufficient to account for the full attenuation seen in the absence of the virulence plasmid. To test the adequacy of the lung infection model for monitoring R. equi vaccine efficacy, BALB/c mice were immunized with live R. equi and challenged intranasally. Vaccination conferred protection against acute pulmonary challenge with virulent R. equi. Our data indicate that the murine lung infection model provides a useful tool for both R. equi virulence and vaccine studies.
Insights
A new mouse lung infection model effectively studies Rhodococcus equi virulence and vaccine efficacy. This model shows the virulence factor VapA is crucial for R. equi survival in the lungs, aiding vaccine development.
Area of Science:
- Veterinary Medicine
- Microbiology
- Immunology
Background:
- Rhodococcus equi causes severe lung infections in foals and immunocompromised individuals.
- Current mouse models often use systemic infection, but lung-specific models are needed for R. equi research.
Purpose of the Study:
- To establish and validate a murine lung infection model for Rhodococcus equi.
- To investigate the role of the virulence factor VapA in R. equi pathogenesis within the lung.
- To assess the utility of this model for evaluating R. equi vaccine efficacy.
Main Methods:
- Intranasal inoculation of BALB/c mice with virulent and avirulent R. equi strains.
- Development of a competitive index assay using isogenic strains lacking the VapA gene or virulence plasmid.
- Vaccination of mice followed by intranasal challenge to assess protective immunity.
Main Results:
- Intranasal challenge led to sustained R. equi survival in the lungs of infected mice.
- The VapA virulence factor was confirmed as essential for R. equi lung colonization.
- The lung infection model successfully demonstrated vaccine-induced protection against R. equi challenge.
Conclusions:
- The murine lung infection model is a valuable tool for studying R. equi virulence mechanisms.
- This model is suitable for assessing the efficacy of R. equi vaccines.
- Understanding R. equi pathogenesis in the lung is critical for developing effective treatments and vaccines.
