Streptococcus

n.

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 β-haemolytic streptococci) are associated with many infections, including scarlet fever, and produce many exotoxins. Strains of the α-haemolytic streptococci are associated with bacterial endocarditis. The species S. pneumoniae (formerly Diplococcus pneumoniae) – the pneumococcus – is associated with serious diseases, including pneumonia, pneumococcal meningitis, and septicaemia; it is also a common bacterial cause of ear infections (see also pneumococcal vaccine). 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

Derivatives:

streptococcal adj.