From the Guidelines
Streptococcus pyogenes adheres to host tissues through multiple specialized surface proteins that facilitate attachment to human cells, primarily involving M protein, F proteins, lipoteichoic acid, and hyaluronic acid capsule. The primary adhesion mechanism involves M protein, which binds to various host components including fibronectin and collagen 1. F proteins (fibronectin-binding proteins) also play a crucial role by attaching to fibronectin on host cell surfaces. Additionally, S. pyogenes produces lipoteichoic acid, which binds to fibronectin, and utilizes hyaluronic acid capsule to interact with CD44 receptors on epithelial cells. The bacterium also expresses pili (fimbriae) that extend from its surface to enhance attachment.
Key Adhesion Mechanisms
- M protein: binds to fibronectin and collagen
- F proteins: attach to fibronectin on host cell surfaces
- Lipoteichoic acid: binds to fibronectin
- Hyaluronic acid capsule: interacts with CD44 receptors on epithelial cells
- Pili (fimbriae): enhance attachment to host cells These adhesion mechanisms are essential for colonization and represent the initial step in pathogenesis, allowing the bacterium to establish infection in the throat, skin, and other tissues, as seen in various clinical settings, including skin and soft tissue infections 1. The redundancy in adhesion mechanisms demonstrates the evolutionary adaptation of S. pyogenes to effectively colonize various human tissues, which explains its success as a human pathogen.
From the Research
Adhesion Mechanisms of S. pyogenes
- S. pyogenes adheres to host tissues through various mechanisms, including the recognition of fibronectin (Fn) by its own Fn-binding proteins 2.
- These Fn-binding proteins bind to Fn, forming a bridge to α5 β1-integrins, which leads to the rearrangement of cytoskeletal actin in host cells and the uptake of invading S. pyogenes 2.
- The M protein, a major virulence factor, plays a crucial role in the adhesion process, with different serotypes forming serotype-specific interaction networks that are highly dependent on the domain arrangement of the surface-attached M protein 3.
- The binding of secretory IgA, monomeric IgA, and C4b-binding protein (C4BP) to the M protein also contributes to the adhesion and evasion of the host immune system 3.
Role of Fn-binding Proteins
- Fn-binding proteins are essential for the adhesion of S. pyogenes to host tissues, and their binding to Fn facilitates the invasion of host cells 2.
- These proteins also contribute to the evasion of the host innate immune system, including the complement system and phagocytosis 2.
- Fn-binding proteins have been proposed as non-M protein vaccine candidates due to their localization and conservation among different M serotypes 2.
Other Adhesion Factors
- M-related protein (Mrp) is another anti-phagocytic factor that helps S. pyogenes evade phagocytosis by binding to fibrinogen, preventing surface deposition of complement via the classical pathway 4.
- The binding of fibrinogen to Mrp is essential for the growth of S. pyogenes in human blood, and the absence of fibrinogen increases complement deposition on the bacterial surface 4.