Streptococcus

Streptococcus (from Ancient Greek στρεπτός (streptós) 'twisted' and κόκκος (kókkos) 'grain') is a genus of gram-positive spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs along a single axis, thus when growing they tend to form pairs or chains, which may appear bent or twisted. This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes (capable of growth both aerobically and anaerobically).

The term was coined in 1877 by Viennese surgeon Albert Theodor Billroth (1829–1894), from Ancient Greek στρεπτός (streptós), meaning "twisted", and κόκκος (kókkos), meaning "grain". In 1984, many bacteria formerly grouped in the genus Streptococcus were separated out into the genera Enterococcus and Lactococcus. Currently, over 50 species are recognised in this genus.

Streptococcus species play a large role in human health and disease. Most exist as commensally as parts of the human microbiome, for example in the mouth, skin, intestine, and upper respiratory tract. Some exist as pathogens and cause infections collectively known as streptococcosis, such as streptococcal pharyngitis (strep throat), pink eye, meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis (the 'flesh-eating' bacterial infections).