īeta-hemolytic streptococci are further classified by Lancefield grouping, a serotype classification (that is, describing specific carbohydrates present on the bacterial cell wall). Gamma-hemolytic species cause no hemolysis. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. Beta-hemolytic species cause complete rupture of red blood cells. Alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Species of Streptococcus are classified based on their hemolytic properties. Streptococci are also a necessary ingredient in producing Emmentaler ('Swiss') cheese. However, many streptococcal species are not pathogenic, and form part of the commensal human microbiota of the mouth, skin, intestine, and upper respiratory tract. In addition to streptococcal pharyngitis (strep throat), certain Streptococcus species are responsible for many cases of pink eye, meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis (the 'flesh-eating' bacterial infections). This genus has been found to be part of the salivary microbiome. Currently, over 50 species are recognised in this genus. ) In 1984, many bacteria formerly grouped in the genus Streptococcus were separated out into the genera Enterococcus and Lactococcus. The term was coined in 1877 by Viennese surgeon Albert Theodor Billroth (1829–1894), by combining the prefix 'strepto-' (from Ancient Greek: στρεπτός, romanized: streptós, lit.'easily twisted, pliant' ), together with the suffix '-coccus' (from Modern Latin: coccus, from Ancient Greek: κόκκος, romanized: kókkos, lit.'grain, seed, berry'. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes (capable of growth both aerobically and anaerobically). This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Cell division in streptococci occurs along a single axis, so as they grow, they tend to form pairs or chains that may appear bent or twisted.

Streptococcus is a genus of gram-positive coccus (plural cocci) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Streptococcus pyogenes (Group A Streptococcus).Streptococcus faecalis (Group D Strepcoccus).Streptococcus agalactiae (Group B Streptococcus).

Spherical bacteria