Streptococcus pyogenes is a spherical Gram-positive bacterium around 0.6-1.0 µm in diameter, which is enclosed in a capsule and exists in pairs or in chains. It is a non-motile, facultative organism where its metabolism allows it to grow in the presence and absence of oxygen. Pyogenic streptococci are beta-haemolytic and so subsequently cause complete lysis of red blood cells in blood agar, making them clear and colourless. They produce a large number of enzymes and toxins which contribute to the invasion and pathogenesis of infections that Streptococcus pyogenes causes  .
They are most commonly found in the oral cavity and from the throat they are able to spread infection elsewhere.
- ↑ Folds, J. D. and Normansell, D. E. (1999) Pocket Guide to Clinic Immunology. Washington, D.C.: American Society for Microbiology
- ↑ Sleigh, J. D. and Timbury, M. C. (1998) Notes on Medical Bacteriology. 5th ed. New York: Churchill Livingstone.