Related Experiment Videos
Pathogenicity of the Streptococcus milleri group in pulmonary infections--effect on phagocytic killing by human
1First Department of Internal Medicine, Faculty of Medicine, University of the Ryukyus.
Abstract:
The pathogenicity of Streptococcus constellatus in pulmonary infections was investigated in mice in correlation with the phagocytic killing of the microorganisms by human polymorphonuclear neutrophils (PMNs). The histological inflammation score of the lungs in mice inoculated intratracheally with 10(8) cfu/mouse of the virulent strain S. constellatus RZYK001 obtained from bronchoalveolar fluid of a patient with pneumonia, was significantly higher than in mice inoculated with the avirulent strains S. constellatus RT4303 and RT6002 obtained from saliva of healthy adults (p < 0.001). The bactericidal activity of human PMNs against Staphylococcus aureus ATCC 25923 was not inhibited at all by the culture filtrate of the virulent strain, but the killing index against RZYK001 was 36.4% after 90-min incubation whereas that against RT4303 and RT6002 was 94.7% and 99.4%, respectively (p < 0.001). Therefore, these results suggest a possible pathogenic mechanism of S. constellatus apparently mediated by a structural component of the organisms so that a virulent strain is less likely to be killed than an avirulent one, predisposing it to survive in the infection sites.
Insights
This study reveals that virulent Streptococcus constellatus strains cause more severe lung inflammation in mice than avirulent ones. Virulent strains are also more resistant to being killed by human immune cells, suggesting a mechanism for their pathogenicity in infections.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Streptococcus constellatus is implicated in pulmonary infections.
- Understanding its pathogenicity is crucial for effective treatment.
Purpose of the Study:
- To investigate the pathogenicity of S. constellatus in a mouse model.
- To correlate pathogenicity with the phagocytic killing by human polymorphonuclear neutrophils (PMNs).
Main Methods:
- Mice were intratracheally inoculated with virulent (RZYK001) and avirulent (RT4303, RT6002) S. constellatus strains.
- Lung inflammation was assessed histologically.
- Human PMN bactericidal activity against S. constellatus strains was measured using killing indices.
Main Results:
- The virulent strain RZYK001 caused significantly higher lung inflammation scores compared to avirulent strains.
- Human PMNs exhibited significantly lower killing indices against the virulent strain (36.4%) than against avirulent strains (94.7% and 99.4%).
- Culture filtrate of the virulent strain did not inhibit PMN activity against Staphylococcus aureus.
Conclusions:
- A virulent S. constellatus strain exhibits increased pathogenicity in pulmonary infections.
- Virulent strains are less susceptible to phagocytic killing by human PMNs, suggesting a role for bacterial components in evading immune responses.
- This reduced susceptibility may contribute to the survival and proliferation of virulent strains at infection sites.