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Hyaluronic acid capsule is a virulence factor for mucoid group A streptococci
M R Wessels1, A E Moses, J B Goldberg
1Channing Laboratory, Brigham and Women's Hospital, Boston, MA 02115.
Abstract:
Mucoid strains of group A Streptococcus have been associated with recent outbreaks of acute rheumatic fever. The mucoid colony morphology of these strains is a result of abundant production of capsular polysaccharide, which is composed of hyaluronic acid. To study the role of the hyaluronic acid capsule in virulence, we derived an acapsular mutant from a mucoid strain of group A Streptococcus by transposon mutagenesis. M protein expression was not altered in the mutant strain. The mucoid wild-type strain grew in fresh human blood and was resistant to phagocytic killing in vitro. In contrast, the acapsular mutant failed to grow in fresh human blood and was sensitive to phagocytic killing in vitro. Loss of capsule was associated with a 100-fold reduction in virulence of the organisms in mice. We conclude that the hyaluronic acid capsule protects mucoid group A streptococci from phagocytosis and has an important role in virulence.
Insights
The hyaluronic acid capsule of mucoid group A Streptococcus is crucial for virulence. This capsule protects bacteria from phagocytosis, enhancing their ability to cause acute rheumatic fever.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Mucoid strains of group A Streptococcus (GAS) are linked to acute rheumatic fever outbreaks.
- The mucoid phenotype is due to abundant hyaluronic acid capsule production.
- The role of this capsule in GAS virulence requires further investigation.
Purpose of the Study:
- To investigate the role of the hyaluronic acid capsule in the virulence of mucoid group A Streptococcus.
- To determine if the capsule influences bacterial survival and resistance to phagocytosis.
Main Methods:
- Generated an acapsular mutant of a mucoid GAS strain using transposon mutagenesis.
- Assessed M protein expression in both wild-type and mutant strains.
- Evaluated bacterial growth in human blood and resistance to phagocytosis in vitro.
- Determined the virulence of both strains in a murine model.
Main Results:
- The acapsular mutant lacked the hyaluronic acid capsule but maintained M protein expression.
- Wild-type mucoid GAS grew in human blood and resisted phagocytosis.
- The acapsular mutant failed to grow in human blood and was susceptible to phagocytosis.
- Loss of the capsule resulted in a 100-fold reduction in virulence in mice.
Conclusions:
- The hyaluronic acid capsule is essential for the virulence of mucoid group A Streptococcus.
- The capsule protects GAS from phagocytic killing, contributing to disease pathogenesis.
- Targeting the hyaluronic acid capsule may be a strategy to combat GAS infections.