Streptococcus pyogenes is a spherical, Gram-positive bacterium that is the cause of group A streptococcal infections. S. pyogenes displays streptococcal group A antigen on its cell wall. S. pyogenes typically produces large zones of beta-hemolysis (the complete disruption of erythrocytes and the release of haemoglobin) when cultured on blood agar plates, and are therefore also called Group A (beta-hemolytic) Streptococcus (abbreviated GABHS). Streptococci are catalase-negative. In ideal conditions, S. pyogenes has an incubation period of approximately 1–3 days. It is an infrequent, but usually pathogenic, part of the skin flora. It is estimated that there are more than 700 million infections each year and over 650, 000 cases of severe, invasive infections which have a mortality rate of 25 %.