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Strong association between capsular type and virulence for mice among human isolates of Streptococcus pneumoniae
D E Briles1, M J Crain, B M Gray
1Department of Microbiology, University of Alabama, Birmingham 35294.
Abstract:
The relationship between capsular type and virulence for mice was examined with 69 fresh human isolates of Streptococcus pneumoniae. These isolates represented eight capsular types or groups. Serologic and molecular weight differences in PspA (pneumococcal surface protein A) indicated that the strains were clonally distinct. Mice were infected intravenously with washed bacteria of all 69 isolates in sterile salt solutions. Twenty-eight of the isolates were also injected intraperitoneally to permit comparisons between the intravenous and intraperitoneal routes. With a few exceptions, there was concordance between the ability of strains to cause fatal infections by the two routes. About 30% of the 69 isolates were virulent for mice. The abilities of the isolates to kill mice and the length of time between inoculation and death were strongly associated with capsular type. All type 4 isolates, 40% of type 3 isolates, and 60% of group 6 isolates were virulent for mice; type 1 isolates were marginally virulent; and all type or group 14, 19, and 23 isolates were avirulent. Times to death were generally longer for mice infected with group 6 or type 1 than for those infected with type 3 or 4 pneumococci. There was no relationship between clinical diagnosis or tissue source of the isolates and virulence for mice.
Insights
Capsular type significantly influences Streptococcus pneumoniae virulence in mice. Specific pneumococcal types like 4, 3, and 6 showed higher virulence, while others like 14, 19, and 23 were avirulent.
Area of Science:
- Microbiology
- Infectious Diseases
- Immunology
Background:
- Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and sepsis.
- Understanding the factors contributing to pneumococcal virulence is crucial for developing effective vaccines and treatments.
- Pneumococcal capsular type and pneumococcal surface protein A (PspA) are known to influence pathogenicity.
Purpose of the Study:
- To investigate the relationship between capsular type and mouse virulence for 69 human isolates of Streptococcus pneumoniae.
- To compare the virulence of different capsular types and their association with mortality and time to death in a murine model.
- To assess the concordance of virulence between intravenous and intraperitoneal infection routes.
Main Methods:
- Sixty-nine fresh human isolates of Streptococcus pneumoniae, representing eight capsular types/groups, were used.
- Bacterial isolates were administered intravenously and, for a subset, intraperitoneally to mice.
- Virulence was assessed by mortality rates and time between inoculation and death.
Main Results:
- Approximately 30% of the tested Streptococcus pneumoniae isolates were virulent in mice.
- A strong association was observed between capsular type and both lethality and time to death.
- Isolates of type 4, 3, and group 6 demonstrated significant virulence, whereas types 14, 19, and 23 were avirulent.
Conclusions:
- Capsular type is a major determinant of Streptococcus pneumoniae virulence in a murine model.
- Virulence varied significantly among different capsular types, impacting disease severity and outcome.
- Clinical diagnosis or tissue source did not correlate with observed mouse virulence.