<unk>  is a species of Gram-positive, aerotolerant bacteria in the genus<unk> . These bacteria are extracellular, and made up of non-motile and non-sporing cocci (round cells) that tend to link in chains. They are clinically important for humans, as they are an infrequent, but usually pathogenic, part of the skin microbiota that can cause Group A streptococcal infection.<unk>  is the predominant species harboring the Lancefield group A antigen, and is often called group A<unk>  <unk> . However, both<unk>  dysgalactiae and the<unk>  anginosus group can possess group A antigen as well. Group A streptococci, when grown on blood agar, typically produce small (2–3 mm) zones of beta-hemolysis, a complete destruction of red blood cells. The name group A (beta-hemolytic)<unk>  (GABHS) is thus also used. The species name is derived from Greek words meaning 'a chain' () of berries ( Latinized from ) and pus ()-forming (genes), since a number of infections caused by the bacterium produce pus. The main criterion for differentiation between Staphylococcus spp. and<unk>  spp. is the catalase test. Staphylococci are catalase positive whereas streptococci are catalase-negative.<unk>  can be cultured on fresh blood agar plates. Under ideal conditions, it has an incubation period of 1 to 3 days. An estimated 700 million<unk>  infections occur worldwide each year. While the overall mortality rate for these infections is 0.1%, over 650,000 of the cases are severe and invasive, with these cases having a mortality rate of 25%. Early recognition and treatment are critical; diagnostic failure can result in sepsis and death.
Streptococcus pyogenes
Staphylococcus aureus
Streptococcus bovis
Streptococcus mutans
Pseudomonas aeruginosa
Staphylococcus haemolyticus
Neisseria flavescens
Corynebacterium diphtheriae