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Role of M protein in adherence of group A streptococci
M G Caparon1, D S Stephens, A Olsén
1Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Abstract:
The role of the M protein in adherence of group A streptococci to human epithelial cells was directly tested by using an isogenic pair of M+ and M- strains. There was no difference between these strains in the number of streptococcal units that adhered to buccal or tonsillar epithelial cells, indicating the following: (i) that adhesins that are not dependent upon M protein expression are present on the surface of group A streptococci and (ii) that the M protein is not the primary streptococcal adherence ligand. However, the M+ strain adhered to tonsillar epithelial cells as aggregates. This aggregation was dependent on the presence of the M protein, since the isogenic M- strain did not clump. The coaggregation of streptococci suggests that the M protein plays an important role in promoting the formation of microcolonies after initial attachment. Binding to fibronectin, a potential epithelial cell receptor for group A streptococci, was also the same for the isogenic M+ and M- strains as well as for an isogenic strain with a regulatory mutation that decreases the expression of M protein. In summary, the M protein is not the primary streptococcal adhesin, nor is it required to orient the streptococcal adhesin and/or fibronectin receptor.
Insights
Group A streptococci adherence to human cells does not primarily involve M protein. However, M protein is crucial for streptococcal aggregation and microcolony formation after initial attachment.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Group A Streptococcus (GAS) is a significant human pathogen.
- The M protein is a major surface virulence factor of GAS.
- Its precise role in bacterial adherence to host cells is not fully understood.
Purpose of the Study:
- To investigate the role of the M protein in the adherence of group A streptococci to human epithelial cells.
- To determine if M protein functions as a primary adhesin for GAS.
Main Methods:
- Utilized isogenic M+ and M- strains of group A Streptococcus.
- Quantified bacterial adherence to buccal and tonsillar epithelial cells.
- Assessed binding to fibronectin.
Main Results:
- No significant difference in adherence was observed between M+ and M- strains to epithelial cells.
- M+ strains exhibited aggregation on tonsillar cells, which was absent in M- strains.
- Fibronectin binding was similar across M+, M-, and M- protein-downregulated strains.
Conclusions:
- M protein is not the primary adhesin mediating GAS attachment to epithelial cells.
- M protein plays a critical role in promoting streptococcal aggregation and microcolony formation.
- M protein is not essential for orienting adhesins or fibronectin receptors during initial attachment.