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Correlation between the production of extracellular substances by type III group B streptococcal strains and
Abstract:
Twelve strains of serotype III group B streptococci (8 isolated from cases of neonatal disease, 3 isolated from asymptomatically colonized infants, and 1 laboratory reference strain) were examined for the vitro production of three potential extracellular virulence products: type-specific antigen, neuraminidase, and protease. In addition, virulence in a mouse model, expressed as 50% lethal dose, was determined for the 12 strains to determine whether a relationship existed between the production of any of the three extracellular products and virulence. Only production of extracellular type-specific antigen showed a correlation with virulence in the mouse model. The high producers of extracellular type-specific antigen were an average of 166-fold more virulent for mice than low producers of the same component. There was no correlation between virulence and either neuraminidase or protease production, nor was there a correlation between either of these two extracellular products and the levels of extracellular type-specific antigen. When levels of group B streptococci of each type (a high and low producer of extracellular type-specific antigen) in organs of infected mice were examined, comparable levels of organisms were found in the brain, spleen, and lungs of mice near death regardless of the initial inoculum. However, the high producer of extracellular type-specific antigen caused death in mice with a 2 to 3 log lower inoculum than the low producer, suggesting that these strains may be more invasive.
Insights
Group B streptococci virulence in newborns is linked to extracellular type-specific antigen production. High antigen producers are significantly more virulent in a mouse model, suggesting increased invasiveness.
Area of Science:
- Microbiology
- Infectious Diseases
- Neonatal Health
Background:
- Group B Streptococcus (GBS) is a leading cause of neonatal disease.
- Virulence factors of GBS are not fully understood.
- Extracellular products like type-specific antigen, neuraminidase, and protease are potential contributors to GBS pathogenicity.
Purpose of the Study:
- To investigate the in vitro production of extracellular virulence factors by GBS serotype III.
- To determine the correlation between extracellular product production and GBS virulence in a mouse model.
- To assess the relationship between specific virulence factors and GBS invasiveness.
Main Methods:
- Twelve GBS serotype III strains were analyzed for extracellular type-specific antigen, neuraminidase, and protease production.
- Mouse model was used to determine the 50% lethal dose (LD50) for each strain.
- GBS organ burden was quantified in infected mice.
Main Results:
- Production of extracellular type-specific antigen correlated significantly with virulence in the mouse model.
- High producers of extracellular type-specific antigen were 166-fold more virulent than low producers.
- No correlation was found between virulence and neuraminidase or protease production.
Conclusions:
- Extracellular type-specific antigen is a key virulence factor for GBS serotype III.
- High extracellular type-specific antigen production may indicate increased GBS invasiveness.
- Further research into type-specific antigen's role in neonatal infections is warranted.