Streptococcus

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iStreptococcus

Scientific classification

Kingdom:	Eubacteria
Phylum:	Firmicutes
Class:	Bacilli
Order:	Lactobacillales
Family:	Streptococcaceae
Genus:	Streptococcus Rosenbach 1884

Streptococcus, a genus of spherical, Gram-positive bacteria of the phylum Firmicutes.<ref name=Sherris>Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.</ref> Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, thus the name — from Greek streptos, meaning easily bent or twisted, like a chain. Constrast this with staphylococci which divide along multiple axes and generate grape-like clusters of cells.

In addition to strep throat, members of this genus are responsible for many cases of meningitis, bacterial pneumonia, endocarditis, erysipelas and even necrotizing fasciitis (so-called 'flesh-eating' bacterial infections). It should be noted, however, that many streptococcal species are non-pathogenic.

Streptococci are part of the normal commensal flora of the mouth, skin, intestine and upper respiratory tract of humans.

1 Classification of Streptococci
2 References

[edit] Classification of Streptococci

Individual species of Streptococcus are classified primarily based on their hemolytic properties (breakdown of red blood cells in a laboratory).<ref name=Baron>Patterson MJ (1996). Streptococcus. In: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1. </ref> Alpha hemolysis is caused by a reduction of iron in hemoglobin giving it a greenish color on blood agar. Beta hemolysis is complete rupture of red blood cells giving distinct, wide, clear areas around bacterial colonies on blood agar. Other streptococci are labeled as gamma haemolytic, actually a misnomer as no hemolysis takes place.

Beta-hemolytic streptococci are further characterised via the Lancefield serotyping - based on specific carbohydrates in the bacterial cell wall.<ref name=Facklam_2002>Facklam R (2002). "What happened to the streptococci: overview of taxonomic and nomenclature changes". Clin Microbiol Rev 15 (4): 613-30. PubMed.</ref> These are named Lancefield groups A to T. See the related article on Rebecca Lancefield. Medically the most important groups are the alpha-hemolytic streptococci, S. pneumoniae and Streptococcus Viridans-group, and the beta-hemolytic streptococci of Lancefield groups A and B (also known as “Group A Strep” and “Group B Strep”)

[edit] Alpha-Hemolytic Streptococci

[edit] Pneumococci

S. pneumoniae, a leading cause of bacterial pneumonia, otitis media and meningitis.

[edit] Viridans and Other Alpha-Hemolytic Streptococci

S. mutans, a contributor to dental caries.
S. viridans, a cause of endocarditis and dental abscesses.
Streptococcus thermophilis is used in the manufacture of swiss cheese.

[edit] Beta-Hemolytic Streptococci

[edit] Group A Streptococci

S. pyogenes (also known as GAS) is the causative agent in Group A streptococcal infections, (GAS) including strep throat, acute rheumatic fever, scarlet fever, and acute glomerulonephritis. If strep throat is not treated, it can develop into rheumatic fever, a disease that affects the joints and heart valves. Other Streptococcus species may also possess the Group A antigen, but human infections by non-S. pyogenes GAS strains (some S. dysgalactiae subsp. equisimilis and S. anginosus Group strains) appear to be uncommon.

[edit] Group B Streptococci

S. agalactiae, or GBS, causes meningitis in neonates and the elderly, with occasional systemic bacteremia. They can also colonize the female reproductive tract, increasing the risk for premature rupture of membranes and transmission to the child. The CDC recommends women who are pregnant should be tested for Group B Strep and given antibiotics during labor in order to reduce the risk of transmission to the baby. In the UK, as the prevalence in the female genital tract is around 15%, antibiotics are not recommended as the side effects of giving antibiotics to the sheer number of women who would test positive and not pass it to their babies outweighs the very few it would benefit.

[edit] Group C Streptococci

Includes S. equi which causes strangles in horses, and S. zooepidemicus which causes infections in several species of mammals including cattle and horses.

[edit] Group D Streptococci (Enterococci)

Many former Group D streptococci have been reclassified and placed in the genus Enterococcus (includes S. faecalis, S. faciem, S. durans, and S. avium).<ref name=Ruoff_1990>Ruoff KL (1990). "Recent taxonomic changes in the genus Enterococcus". Eur J Clin Microbiol Infect Dis 9 (2): 75-9. PubMed.</ref> For example, Streptococcus faecalis is now Enterococcus faecalis.

The remaining non-enterococcal Group D strains include S. bovis and S. suis.

[edit] Non-Hemolytic Streptococci

Non-hemolytic streptococci rarely cause disease. However weakly hemolytic group D beta-hemolytic streptococci and Listeria monocytogenes should not be confused with non-hemolytic streptococci.