Streptococcus pyogenes, also known as Group A Streptococcus (GAS) is a beta-hemolytic type streptococcus. It is one of the most common human pathogens. S. pyogenes can be present within the human bacteriological flora without showing signs of infection. But under certain circumstances it can overgrow and cause illnesses and diseases. This bacterium is responsible for diseases such as pharyngitis (strep throat), scarlet fever (rash), impetigo (infection of the superficial layers of the skin) and cellulitis (infection of the deep layers of the skin).
Streptococcus pyogenes virulence factors
When a S. pyogenes infection occurs, the bacteria are able to rapidly grow and avoid the natural host defenses using some clever tricks. The cell surface of S. pyogenes is very complex and has many proteins that help this bacterium colonize host cells and avoid phagocytosis (the presence of a hyaluronic acid capsule inhibits phagocytosis). In addition, the cytoplasm of S. pyogenes has many proteins similar to those of humans (cardiac, skeletal, and smooth muscle, heart valve fibroblasts, and neuronal tissues). The net result is a sort of “molecular mimicry” that allows the host cell “to tolerate” the invasion. Some strains release potent toxins that can destroy cells as well as possessing enzymes which can protect the bacterium from being trapped by neutrophils.
