Streptococcus pyogenes, also known as group A beta-haemolytic Streptococcus (GAS) or group A strep, is a frequent coloniser of the upper respiratory tract, skin, and to a lesser degree, the vagina and urinary tract. A person can be an asymptomatic carrier and transmitter of Streptococcus pyogenes.
Group A strep is found more often in vulvovaginal infections in young girls, though is known to be spread between sexual partners and is found in adult women. Group A strep causes vaginitis, which is inflammation of the vagina.
‘Strep throat’ is generally caused by group A strep. Group A strep vulvovaginal and urinary tract infections are less common than throat infections, but because both areas are mucous membranes, co- or cross-infection or colonisation can occur.
The outer capsule of Streptococcus pyogenes is made of hyaluronic acid, which allows it to evade host defences – we have a lot of hyaluronic acid in our tissues. Group A strep can invade epithelial cells, often without being ‘noticed’ by the immune system of the host, resulting in infections. Epithelial cells don’t really allow antibiotics in, so treatment can be challenging.
M protein binds to the fibrinogen on host cells, blocking phagocytosis. Some strains of streptococci have an abundance of M protein and can quickly multiply.
