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A genus of nonmotile (with few exceptions), nonsporeforming, aerobic to facultatively anaerobic bacteria (family Lactobacillaceae) containing Gram-positive, spherical or ovoid cells that occur in pairs or short or long chains. Dextrorotatory lactic acid is the main product of carbohydrate fermentation. These organisms occur regularly in the mouth and intestines of humans and other animals, in dairy and other food products, and in fermenting plant juices. Some species are pathogenic. The type species is S. pyogenes. [strepto- + G. kokkos, berry (coccus)]

- S. agalactiae a species found in the milk and tissues from udders of cows with mastitis; also reported to be associated with a variety of human infections, especially those of the urogenital tract.

- S. anginosus an α-hemolytic species of bacteria found in the human throat, sinuses, abscesses, vagina, skin, and feces; this organism is a common cause of isolated liver abscesses.

- S. bovis a bacterial species found in the bovine alimentary tract; this organism may also be found in blood and heart lesions in cases of subacute endocarditis.

- S. constellatus an α-hemolytic species of bacteria found in tonsils, purulent pleurisy, appendix, the nose, throat, and gums, and infrequently on the skin and in the vagina.

- S. durans a bacterial species found in dried milk powder and in the intestines of humans and other animals.

- S. faecalis SYN: Enterococcus faecalis.

- S. intermedius one of a heterogenous collection of streptococci, generally found in the mouth or upper respiratory tract; classification is generally established by fermentation patterns, analysis of the sugar composition of the cell wall, and use of sugar production patterns. SYN: Peptostreptococcus intermedius.

- S. lactis a bacterial species found commonly as a contaminant in milk and dairy products; a common cause of the souring and coagulation of milk; some strains produce nisin, a powerful antibiotic that inhibits the growth of many other Gram-positive organisms.

- S. milleri a term used to refer to the S. intermedius group, which contains three distinct streptococcal species including S. intermedius, S. constellatus, and S. anginosus. These bacteria are found in the human oral cavity and have been associated with a variety of infections including bacteremia; endocarditis; and CNS, oral, and thoracic infections.

- S. mitis a bacterial species found in the human mouth, throat, and nasopharynx; ordinarily, it is not considered to be pathogenic, but this organism may be recovered from ulcerated teeth and sinuses and from blood and heart lesions in cases of subacute endocarditis.

- S. morbillorum SYN: Peptostreptococcus morbillorum.

- S. mutans a bacterial species associated with the production of dental caries in humans and in some other animals and with subacute endocarditis.

- S. pneumoniae a species of Gram-positive, lancet-shaped cocci and diplococci frequently occurring in chains; cells are readily lysed by bile salts. Virulent forms are enclosed in type-specific polysaccharide capsules, the basis for an effective vaccine. Normal inhabitants of the respiratory tract, and the most common cause of lobar pneumonia, they are the most common causative agents of meningitis, and pneumonia worldwide, and also cause sinusitis, and other infections. It is the type species of the former genus Diplococcus. SYN: Fraenkel pneumococcus, pneumococcus, pneumonococcus.

- S. pyogenes a bacterial species found in the human mouth, throat, and respiratory tract and in inflammatory exudates, the bloodstream, and cellulitic lesions in human diseases; it is sometimes found in the udders of cows and in dust from sickrooms, hospital wards, schools, theaters, and other public places; it causes the formation of pus, fatal septicemia, and necrotizing fascitis and myositis. There is also a specific somatic antigen (M protein) for each of the approximately 85 types. It is the type species of the genus S..

- S. salivarius a bacterial species found in the human mouth, throat, and nasopharynx, and associated with dental disease.

- S. sanguis a bacterial species originally found in the so-called vegetation on heart valves from cases of subacute bacterial endocarditis; occasionally found in infected sinuses and teeth and in house dust.

- S. viridans a name applied not to a distinct species but rather to the group of α-hemolytic streptococci as a whole; viridans streptococci have been isolated from the mouth and intestines of humans, the intestines of horses, the milk and feces of cows, and milk products. SYN: viridans streptococci.

strep·to·coc·cus -'käk-əs n

1) cap a genus of spherical or ovoid chiefly nonmotile and parasitic gram-positive bacteria (family Streptococcaceae) that divide only in one plane, occur in pairs or chains, and include important pathogens of humans and domestic animals

2) pl -coc·ci -'käk-.(s)ī any bacterium of the genus Streptococcus broadly a coccus occurring in chains

a genus of Gram-positive nonmotile spherical bacteria occurring in chains. Most species are saprophytes; some are pathogenic. Many pathogenic species are haemolytic, i.e. they have the ability to destroy red blood cells in blood agar. This provides a useful basis for classifying the many different strains. Strains of S. pyogenes (the b-haemolytic streptococci) are associated with many infections, including scarlet fever, and produce many exotoxin. Strains of the a-haemolytic streptococci are associated with bacterial endocarditis. The species S. pneumoniae (formerly Diplococcus pneumoniae) - the pneumococcus - is associated with pneumonia and pneumococcal meningitis. It occurs in pairs, surrounded by a capsule (see quellung reaction). S. mutans has been shown to cause dental caries. See also Lancefield classification, streptokinase.

• streptococcal adj.