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A strain-independent method to induce progressive and lethal pneumococcal pneumonia in neutropenic mice
Andres F Zuluaga1,2, Beatriz E Salazar3, Maria Agudelo4,5,6
1GRIPE [Grupo Investigador de Problemas en Enfermedades infecciosas], Medellín, Colombia. andres.zuluaga@udea.edu.co.
Background:
Experimental models of pneumonia with penicillin non-susceptible Streptococcus pneumoniae (PNSSP) are hard to reproduce because the majority of strains with clinical relevance (like serotypes 6B, 9 V and 19 F) have low murine virulence. By optimization of culture and inoculum conditions of PNSSP (using porcine mucin), our aim was to develop a suitable, reliable and reproducible pneumonia mouse model for anti-infective pharmacology research.
Results:
Seven PNSSP strains, including serotypes 6B, 9 V, 14 and 19 F were included. Strain INS-E611 displayed the highest murine virulence and was chosen to validate the lung model. Nose-instilled pneumococci grew between 2.1 and 2.5 log10 CFU/g of lung in 24 hours when an optimized culture of bacterial cells was used, but animals were all alive and recovered of infection after 36 h. In contrast, inoculum supplementation with mucin led to 100% mortality related to a successful lung infection confirmed by histopathology. These findings were reproduced with all seven PNSSP strains in neutropenic mice. Immunocompetent animals cleared all strains spontaneously.
Conclusions:
This pneumonia model produces a progressive and uniformly fatal lung infection with diverse serotypes of PNSSP independently of their intrinsic murine virulence.
Insights
Developing a reliable pneumonia mouse model for penicillin non-susceptible Streptococcus pneumoniae (PNSSP) is crucial. This study optimized conditions using mucin, achieving reproducible, fatal lung infections with diverse PNSSP strains for anti-infective research.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Penicillin non-susceptible Streptococcus pneumoniae (PNSSP) strains, particularly common serotypes, exhibit low virulence in standard mouse models, hindering research.
- Developing reproducible experimental pneumonia models for PNSSP is essential for anti-infective drug development.
Purpose of the Study:
- To establish a reliable and reproducible mouse model of pneumonia caused by PNSSP for anti-infective pharmacology research.
- To overcome the challenge of low murine virulence associated with clinically relevant PNSSP strains.
Main Methods:
- Optimization of bacterial culture and inoculum conditions for PNSSP, specifically incorporating porcine mucin.
- Validation of the developed pneumonia model using seven diverse PNSSP strains, including serotypes 6B, 9V, 14, and 19F.
- Assessment of model efficacy in both neutropenic and immunocompetent mouse models.
Main Results:
- Supplementation of the inoculum with mucin resulted in 100% mortality in mice, confirming a successful and fatal lung infection.
- The optimized model demonstrated reproducible results across all seven tested PNSSP strains in neutropenic mice.
- Immunocompetent mice spontaneously cleared the infection, highlighting the model's ability to differentiate immune responses.
Conclusions:
- The developed pneumonia model provides a progressive and uniformly fatal infection with various PNSSP serotypes.
- This model is effective regardless of the intrinsic murine virulence of the specific PNSSP strain used.
- The mucin-supplemented inoculum method is key to establishing a reproducible and lethal PNSSP pneumonia model.