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{{Short description|Genus of bacteria}}
{{Taxobox
{{Distinguish|Staphylococcus}}
| color = lightgrey
{{See also|Strep throat}}
| name = ''Streptococcus''
{{Automatic taxobox
| image = Streptococcus.jpg
| image = Streptococci.jpg
| image_width = 270px
| taxon = Streptococcus
| regnum = [[Eubacteria]]
| authority = [[Friedrich Julius Rosenbach|Rosenbach]], 1884
| phylum = [[Firmicutes]]
| classis = [[Bacilli]]
| ordo = [[Lactobacillales]]
| familia = [[Streptococcaceae]]
| genus = '''''Streptococcus'''''
| genus_authority = Rosenbach, [[1884]]
| subdivision_ranks = Species
| subdivision_ranks = Species
| subdivision_ref = <ref name=Streptococcus/>
| subdivision =
| subdivision =
* ''[[Streptococcus acidominimus]]''<ref name=Streptococcus>{{cite web| vauthors = Parte AC |title=Streptococcus|website=[[LPSN]]|url=https://lpsn.dsmz.de/genus/streptococcus}}</ref>
''[[Streptococcus agalactiae|S. agalactiae]]''<br/>
''[[Streptococcus aginosus|S. aginosus]]''<br/>
* ''[[Streptococcus agalactiae]]'' (Group B Streptococcus)
''[[Streptococcus bovis|S. bovis]]''<br/>
* ''[[Streptococcus alactolyticus]]''<ref name=Streptococcus/>
''[[Streptococcus canis|S. canis]]''<br/>
* ''[[Streptococcus anginosus]]''
''[[Streptococcus mutans|S. mutans]]''<br/>
* ''[[Streptococcus australis]]''<ref name=Streptococcus/>
''[[Streptococcus oralis|S. oralis]]''<br/>
* ''[[Streptococcus caballi]]''<ref name=Streptococcus/>
''[[Streptococcus peroris|S. peroris]]''<br/>
* ''[[Streptococcus cameli]]''<ref name=Streptococcus/>
''[[Streptococcus pneumoniae|S. pneumoniae]]''<br/>
* ''[[Streptococcus canis]]''
''[[Streptococcus pyogenes|S. pyogenes]]''<br/>
* ''[[Streptococcus caprae]]''<ref name=Streptococcus/>
''[[Streptococcus ratti|S. ratti]]''<br/>
* ''[[Streptococcus castoreus]]''<ref name=Streptococcus/>
''[[Streptococcus salivarius|S. salivarius]]''<br/>
* ''[[Streptococcus constellatus]]''
''[[Streptococcus sanguinis|S. sanguinis]]''<br/>
* ''[[Streptococcus criceti]]''<ref name=Streptococcus/>
''[[Streptococcus sobrinus|S. sobrinus]]''<br/>
* ''[[Streptococcus cristatus]]''
''[[Streptococcus parasanguinis|S. parasanguinis]]''<br/>
* ''[[Streptococcus cuniculi]]''<ref name=Streptococcus/>
''[[Streptococcus suis|S. suis]]''<br/>
* ''[[Streptococcus danieliae]]''<ref name=Streptococcus/>
''[[Streptococcus thermophilus|S. thermophilus]]''<br/>
* ''[[Streptococcus dentasini]]''<ref name=Streptococcus/>
''[[Streptococcus vestibularis|S. vestibularis]]''<br/>
* ''[[Streptococcus dentiloxodontae]]''<ref name=Streptococcus/>
''[[Streptococcus viridans]]''<br/>
* ''[[Streptococcus dentirousetti]]''<ref name=Streptococcus/>
''[[Streptococcus uberis]]''<br/>
* ''[[Streptococcus devriesei]]''<ref name=Streptococcus/>
* ''[[Streptococcus didelphis]]''<ref name=Streptococcus/>
etc.
* ''[[Streptococcus downei]]''
* ''[[Streptococcus dysgalactiae]]''
* ''[[Streptococcus entericus]]''<ref name=Streptococcus/>
* ''[[Streptococcus equi]]''<ref name=Streptococcus/>
* ''[[Streptococcus equinus]]''
* ''[[Streptococcus faecalis]]'' (Group D Strepcoccus)
* ''[[Streptococcus ferus]]''
* ''[[Streptococcus gallinaceus]]''<ref name=Streptococcus/>
* ''[[Streptococcus gallolyticus]]''<ref name=Streptococcus/>
* ''[[Streptococcus gordonii]]''<ref name=Streptococcus/>
* ''[[Streptococcus halichoeri]]''<ref name=Streptococcus/>
* ''[[Streptococcus halotolerans]]''<ref name=Streptococcus/>
* ''[[Streptococcus henryi]]''<ref name=Streptococcus/>
* ''[[Streptococcus himalayensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus hongkongensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus hyointestinalis]]''<ref name=Streptococcus/>
* ''[[Streptococcus hyovaginalis]]''<ref name=Streptococcus/>
* ''[[Streptococcus ictaluri]]''<ref name=Streptococcus/>
* ''[[Streptococcus infantarius]]''
* ''[[Streptococcus infantis]]''<ref name=Streptococcus/>
* ''[[Streptococcus iniae]]''
* ''[[Streptococcus intermedius]]''
* ''[[Streptococcus lactarius]]''<ref name=Streptococcus/>
* ''[[Streptococcus loxodontisalivarius]]''<ref name=Streptococcus/>
* ''[[Streptococcus lutetiensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus macacae]]''<ref name=Streptococcus/>
* ''[[Streptococcus marimammalium]]''<ref name=Streptococcus/>
* ''[[Streptococcus marmotae]]''<ref name=Streptococcus/>
* ''[[Streptococcus massiliensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus merionis]]''<ref name=Streptococcus/>
* ''[[Streptococcus minor]]''<ref name=Streptococcus/>
* ''[[Streptococcus mitis]]''
* ''[[Streptococcus moroccensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus mutans]]''
* ''[[Streptococcus oralis]]''
* ''[[Streptococcus oricebi]]''<ref name=Streptococcus/>
* ''[[Streptococcus oriloxodontae]]''<ref name=Streptococcus/>
* ''[[Streptococcus orisasini]]''<ref name=Streptococcus/>
* ''[[Streptococcus orisratti]]''
* ''[[Streptococcus orisuis]]''<ref name=Streptococcus/>
* ''[[Streptococcus ovis]]''<ref name=Streptococcus/>
* ''[[Streptococcus panodentis]]''<ref name=Streptococcus/>
* ''[[Streptococcus pantholopis]]''<ref name=Streptococcus/>
* ''[[Streptococcus parasanguinis]]''
* ''[[Streptococcus parasuis]]''<ref name=Streptococcus/>
* ''[[Streptococcus parauberis]]''<ref name=Streptococcus/>
* ''[[Streptococcus peroris]]''
* ''[[Streptococcus pharyngis]]''<ref name=Streptococcus/>
* ''[[Streptococcus phocae]]''<ref name=Streptococcus/>
* ''[[Streptococcus pluranimalium]]''<ref name=Streptococcus/>
* ''[[Streptococcus plurextorum]]''<ref name=Streptococcus/>
* ''[[Streptococcus pneumoniae]]''<ref name=Streptococcus/>
* ''[[Streptococcus porci]]''<ref name=Streptococcus/>
* ''[[Streptococcus porcinus]]''<ref name=Streptococcus/>
* ''[[Streptococcus porcorum]]''<ref name=Streptococcus/>
* ''[[Streptococcus pseudopneumoniae]]''<ref name=Streptococcus/>
* ''[[Streptococcus pseudoporcinus]]''<ref name=Streptococcus/>
* ''[[Streptococcus pyogenes]]'' (Group A Streptococcus)
* ''[[Streptococcus ratti]]''
* ''[[Streptococcus rifensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus rubneri]]''<ref name=Streptococcus/>
* ''[[Streptococcus rupicaprae]]''<ref name=Streptococcus/>
* ''[[Streptococcus salivarius]]''
* ''[[Streptococcus saliviloxodontae]]''<ref name=Streptococcus/>
* ''[[Streptococcus sanguinis]]''<ref name=Streptococcus/>
* ''[[Streptococcus sinensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus sobrinus]]''<ref name=Streptococcus/>
* ''[[Streptococcus suis]]''
* ''[[Streptococcus tangierensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus thermophilus]]''
* ''[[Streptococcus thoraltensis]]''<ref name=Streptococcus/>
* ''[[Streptococcus tigurinus]]''
* ''[[Streptococcus troglodytae]]''<ref name=Streptococcus/>
* ''[[Streptococcus troglodytidis]]''<ref name=Streptococcus/>
* ''[[Streptococcus uberis]]''
* ''[[Streptococcus urinalis]]''<ref name=Streptococcus/>
* ''[[Streptococcus ursoris]]''<ref name=Streptococcus/>
* ''[[Streptococcus vestibularis]]''
* ''[[Streptococcus zooepidemicus]]''
* [[Viridans streptococci]]
** [[Streptococcus anginosus group|''Streptococcus anginosus'' group]]
}}
}}


'''''Streptococcus''''' is a [[genus]] of [[sphere|spherical]] [[Gram-positive]] [[bacterium|bacteria]], belonging to the [[phylum (biology)|phylum]] [[Firmicutes]]<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref> and the [[lactic acid bacteria]] group. [[Cell division|Cellular division]] occurs along a single [[Coordinate axis|axis]] in these bacteria, and thus they grow in chains or pairs, hence the name &mdash; from [[Greek language|Greek]] στρεπτος ''streptos'', meaning easily bent or twisted, like a chain. Contrast this with [[Staphylococcus|staphylococci]], which divide along multiple axes and generate grape-like clusters of [[cell (biology)|cell]]s.
'''''Streptococcus''''' is a [[genus]] of [[gram-positive bacteria|gram-positive]] or spherical bacteria that belongs to the family [[Streptococcaceae]], within the order [[Lactobacillales]] (lactic acid bacteria), in the phylum [[Bacillota]].<ref name=Sherris/> [[Cell division]] in streptococci occurs along a single [[coordinate system|axis]], thus when growing they tend to form pairs or chains, which may appear bent or twisted. This differs from [[Staphylococcus|staphylococci]], which divide along multiple axes, thereby generating irregular, grape-like clusters of [[cell (biology)|cells]]. Most streptococci are [[Oxidase test|oxidase-negative]] and [[Catalase#Clinical significance and application|catalase-negative]], and many are [[facultative anaerobic organism|facultative anaerobes]] (capable of growth both aerobically and anaerobically).


The term was coined in 1877 by Viennese surgeon [[Theodor Billroth|Albert Theodor Billroth]] (1829–1894),<ref>{{Cite web|url=https://www.etymonline.com/word/streptococcus|title=streptococcus|website=Online Etymology Dictionary|access-date=25 July 2018}}</ref> by combining the prefix "strepto-" (from {{Langx|grc|[[wikt:στρεπτός|στρεπτός]]|streptós|easily twisted, pliant}}<ref>{{LSJ|strepto/s|στρεπτός|longref}}</ref>), together with the suffix "-coccus" (from Modern {{Langx|la|coccus}}, from {{Langx|grc|κόκκος|kókkos|grain, seed, berry|link=no}}.<ref>{{LSJ|ko/kkos|κόκκος|shortref}}</ref>) In 1984, many bacteria formerly grouped in the genus ''Streptococcus'' were separated out into the [[Genus|genera]] ''[[Enterococcus]]'' and ''[[Lactococcus]]''.<ref name="pmid12364372">{{cite journal | vauthors = Facklam R | title = What happened to the streptococci: overview of taxonomic and nomenclature changes | journal = Clinical Microbiology Reviews | volume = 15 | issue = 4 | pages = 613–630 | date = October 2002 | pmid = 12364372 | pmc = 126867 | doi = 10.1128/CMR.15.4.613-630.2002 }}</ref> Currently, over 50 species are recognised in this genus. This genus has been found to be part of the [[salivary microbiome]].<ref>{{cite journal | vauthors = Wang K, Lu W, Tu Q, Ge Y, He J, Zhou Y, Gou Y, Van Nostrand JD, Qin Y, Li J, Zhou J, Li Y, Xiao L, Zhou X | display-authors = 6 | title = Preliminary analysis of salivary microbiome and their potential roles in oral lichen planus | journal = Scientific Reports | volume = 6 | issue = 1 | pages = 22943 | date = March 2016 | pmid = 26961389 | pmc = 4785528 | doi = 10.1038/srep22943 | bibcode = 2016NatSR...622943W }}</ref>
Streptococci are [[oxidase]]&ndash; and [[catalase]]&ndash;negative.


==Pathogenesis==
==Pathogenesis and classification==
{{see also|Streptococcosis}}
Tastes like orange soda.
In addition to [[streptococcal pharyngitis|strep throat]], certain ''Streptococcus'' species are responsible for many cases of [[meningitis]], [[bacterial pneumonia]], [[endocarditis]], [[erysipelas]] and [[necrotizing fasciitis]] (the 'flesh-eating' bacterial infections). However, many streptococcal species are non-pathogenic. Streptococci are also part of the normal [[Commensalism|commensal]] [[flora (microbiology)|flora]] of the mouth, skin, intestine, and upper respiratory tract of humans.
In addition to [[streptococcal pharyngitis]] (strep throat), certain ''Streptococcus'' species are responsible for many cases of [[conjunctivitis|pink eye]],<ref>{{cite web | url=http://www.medicinenet.com/pink_eye/article.htm | title=How to Get Rid of Pinkeye, Symptoms, Treatment, Causes & Pictures}}</ref> [[meningitis]], [[bacterial pneumonia]], [[endocarditis]], [[erysipelas]], and [[necrotizing fasciitis]] (the 'flesh-eating' bacterial infections). However, many streptococcal species are not pathogenic, and form part of the [[Commensalism|commensal]] human [[Microbiota (microbiology)|microbiota]] of the mouth, skin, intestine, and upper respiratory tract. Streptococci are also a necessary ingredient in producing [[Emmental cheese|Emmentaler ("Swiss") cheese]].<ref>{{Cite web |title=Streptococcus {{!}} Center for Academic Research and Training in Anthropogeny (CARTA) |url=https://carta.anthropogeny.org/glossary/streptococcus |access-date=2022-07-23 |website=carta.anthropogeny.org}}</ref>


As a rule, individual species of ''Streptococcus'' are classified based on their [[Hemolysis (microbiology)|hemolytic]] properties (breakdown of red blood cells in a laboratory).<ref name=Baron>{{cite book | author = Patterson MJ | title = Streptococcus. ''In:'' Baron's Medical Microbiology ''(Baron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.824 (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-only 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 hemolytic, actually a misnomer, as no hemolysis takes place.
Species of streptococci are classified based on their [[Hemolysis (microbiology)|hemolytic]] properties.<ref name=Baron>{{cite book | author = Patterson MJ | title = Streptococcus. ''In:'' Baron's Medical Microbiology| editor = Baron S| display-editors = etal| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | id = [https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.824 (via NCBI Bookshelf)] | isbn = 978-0-9631172-1-2}}</ref> Alpha-hemolytic species cause oxidization of iron in [[hemoglobin]] molecules within red blood cells, giving it a greenish color on blood agar. [[Beta-hemolytic]] species cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. [[Gamma-hemolytic]] species cause no hemolysis.<ref>{{Cite book | vauthors = Sharma S, Khanna G, Gangane SD |url=https://books.google.com/books?id=2eeaDwAAQBAJ&dq=Streptococcus++Gamma-hemolytic+species+cause+no+hemolysis&pg=PA102 |title=Textbook of Pathology and Genetics for Nurses E-Book |date=2019-07-13 |publisher=Elsevier Health Sciences |isbn=978-81-312-5538-4 |language=en}}</ref>


Beta-hemolytic streptococci are further classified by [[Lancefield grouping]], a [[serotype]] classification (that is, describing specific carbohydrates present on the bacterial cell wall).<ref name="pmid12364372"/> The 21 described serotypes are named Lancefield groups A to W (excluding E, I and J). This system of classification was developed by [[Rebecca Lancefield]], a scientist at [[Rockefeller University]].<ref>{{cite journal | vauthors = Carroll KC | title = Biographical Feature: Rebecca Lancefield, Ph.D | journal = Journal of Clinical Microbiology | volume = 57 | issue = 8 | date = August 2019 | pmid = 31142605 | pmc = 6663886 | doi = 10.1128/JCM.00728-19 | veditors = Munson E }}</ref>
Beta-hemolytic streptococci are further characterised via the [[Serovar|Lancefield serotyping]] - based on specific carbohydrates in the bacterial cell wall.<ref name=Facklam_2002>{{cite journal | author=Facklam R | title=What happened to the streptococci: overview of taxonomic and nomenclature changes | journal=Clin Microbiol Rev | year=2002 | pages=613–30 | volume=15 | issue=4 | pmid=12364372 | doi = 10.1128/CMR.15.4.613-630.2002 <!--Retrieved from CrossRef by DOI bot-->}}</ref> These are named Lancefield groups A to T, although some species, such as ''S. pneumoniae'', do not express Lancefield antigens. See the related article on [[Rebecca Lancefield]]. In the medical setting, 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”).

In the medical setting, the most important groups are the alpha-hemolytic streptococci ''S. pneumoniae'' and ''Streptococcus'' ''viridans ''groups, and the beta-hemolytic streptococci of Lancefield groups A and B (also known as "group A strep" and "group B strep").

'''Table: Medically relevant streptococci'''<ref name=Baron/>
{| class="wikitable sortable"
! Species
! Host
! Disease
|-
| ''[[Streptococcus pyogenes|S. pyogenes]]'' ||human||[[pharyngitis]], [[cellulitis]], [[erysipelas]]
|-
| ''[[Streptococcus agalactiae|S. agalactiae]]'' ||human, cattle||[[neonatal meningitis]] and [[sepsis]]
|-
| ''[[Streptococcus dysgalactiae|S. dysgalactiae]]''||human, animals||[[endocarditis]], [[bacteremia]], [[pneumonia]], [[meningitis]], [[respiratory infections]]
|-
| ''[[Streptococcus gallolyticus|S. gallolyticus]]'' ||human, animals||biliary or [[urinary tract infections]], [[endocarditis]]
|-
| ''[[Streptococcus anginosus|S. anginosus]]'' || human, animals ||subcutaneous/organ [[abscess]]es, [[meningitis]], respiratory infections
|-
| ''[[Streptococcus sanguinis|S. sanguinis]]'' ||human|| endocarditis, [[dental caries]]
|-
| ''[[Streptococcus suis|S. suis]]'' ||swine|| meningitis
|-
| ''[[Streptococcus mitis|S. mitis]]''||human|| endocarditis
|-
| ''[[Streptococcus mutans|S. mutans]]''||human|| dental caries
|-
| ''[[Streptococcus pneumoniae|S. pneumoniae]]''||human|| [[pneumonia]]
|}

===Alpha-hemolytic===
When [[alpha-hemolysis]] (α-hemolysis) is present, the agar under the colony will appear dark and greenish due to the conversion of hemoglobin to green [[biliverdin]]. ''Streptococcus pneumoniae'' and a group of oral streptococci (''Streptococcus viridans'' or viridans streptococci) display alpha-hemolysis.
Alpha-hemolysis is also termed incomplete hemolysis or partial hemolysis because the cell membranes of the red blood cells are left intact. This is also sometimes called green hemolysis because of the color change in the agar.{{citation needed|date=August 2022}}


===Alpha-Hemolytic Streptococcus===
====Pneumococci====
====Pneumococci====
*''[[Streptococcus pneumoniae|S. pneumoniae]]'', a leading cause of bacterial [[pneumonia]], otitis media and [[meningitis]].
* ''[[Streptococcus pneumoniae|S. pneumoniae]]'' (sometimes called pneumococcus), is a leading cause of bacterial [[pneumonia]] and the occasional etiology of [[otitis media]], [[sinusitis]], [[meningitis]], and [[peritonitis]]. Inflammation is thought to be the major cause of how pneumococci cause disease, hence the tendency of diagnoses associated with them to involve inflammation. They possess no Lancefield antigens.<ref name="Sherris" />


====Viridans and Others====
====The viridans group: alpha-hemolytic====
* The [[viridans streptococci]] are a large group of [[commensal]] bacteria that are either [[alpha-hemolytic]], producing a green coloration on blood [[agar plates]] (hence the name "viridans", from Latin ''vĭrĭdis'', green), or nonhemolytic. They possess no Lancefield antigens.<ref name="Sherris">{{cite book |url=https://archive.org/details/sherrismedicalmi0000unse |title=Sherris Medical Microbiology |publisher=Appleton & Lange |year=1994 |isbn=0-8385-8541-8 |veditors=Ryan KJ, Sherris JC |edition=3rd |pages=[https://archive.org/details/sherrismedicalmi0000unse/page/266 266]–7 |url-access=limited}}</ref>
* ''[[Streptococcus mutans|S. mutans]]'', a contributor to [[dental caries]]
* ''[[Streptococcus viridans|S. viridans]]'', a cause of [[endocarditis]] and [[Tooth abscess|dental abscesses]]
* ''[[Streptococcus thermophilus|S. thermophilus]]'', used in the manufacture of some cheeses and yogurts
* ''[[Streptococcus constellatus|S. constellatus]]'', occasional human pathogen, notable as colonies grown on blood [[agar]] smell strongly of caramel


===Beta-Hemolytic Streptococci===
=== Beta-hemolytic ===
[[Beta-hemolysis]] (β-hemolysis), sometimes called complete [[Hemolysis (microbiology)|hemolysis]], is a complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells. There are two types of streptolysin: Streptolysin O (SLO) and streptolysin S (SLS). Streptolysin O is an oxygen-sensitive cytotoxin, secreted by most group A ''Streptococcus'' (GAS), and interacts with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), and usually results in beta-hemolysis under the surface of blood agar. Streptolysin S is an oxygen-stable cytotoxin also produced by most GAS strains which results in clearing on the surface of blood agar. SLS affects immune cells, including polymorphonuclear leukocytes and lymphocytes, and is thought to prevent the host immune system from clearing infection. ''Streptococcus pyogenes'', or GAS, displays beta hemolysis.
====Group A ====
''[[Streptococcus pyogenes|S. pyogenes]]'' (also known as ''GAS'') is the causative agent in [[Group A streptococcal infection]]s, (''GAS'') including [[streptococcal pharyngitis]] ("strep throat"), acute [[rheumatic fever]], [[scarlet fever]], acute [[glomerulonephritis]] and [[necrotizing fasciitis]]. If [[strep throat]] is not treated, it can develop into [[rheumatic fever]], a disease that affects the [[joint]]s and [[heart valve]]s. 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.


Some weakly beta-hemolytic species cause intense hemolysis when grown together with a strain of ''Staphylococcus''. This is called the [[CAMP test]]. ''Streptococcus agalactiae'' displays this property. ''[[Clostridium perfringens]]'' can be identified presumptively with this test. ''Listeria monocytogenes'' is also positive on sheep's blood agar.
Group A Strep infection is generally diagnosed with a [[Rapid Strep Test]] or by culture.
[[File:Alpha and Beta haemolytic streptococci.jpg|thumb|250px|Alpha-hemolytic ''[[S. viridans]]'' (right) and [[beta-hemolytic]] ''[[S. pyogenes]]'' (left) streptococci growing on blood agar]]


====Group B ====
==== Group A ====
Group A ''[[Streptococcus pyogenes|S. pyogenes]]'' is the causative agent in a wide range of [[group A streptococcal infection]]s (GAS). These [[infection]]s may be noninvasive or invasive. The noninvasive infections tend to be more common and less severe. The most common of these infections include [[streptococcal pharyngitis]] (strep throat) and [[impetigo]].<ref name="Cohen-Poradosu 2007">{{cite journal | vauthors = Cohen-Poradosu R, Kasper DL | title = Group A streptococcus epidemiology and vaccine implications | journal = Clinical Infectious Diseases | volume = 45 | issue = 7 | pages = 863–865 | date = October 2007 | pmid = 17806050 | doi = 10.1086/521263 | doi-access = free }}</ref> [[Scarlet fever]] is another example of Group A noninvasive infection.
''[[Streptococcus agalactiae|S. agalactiae]]'', or ''GBS'', causes [[pneumonia]] and [[meningitis]] in [[neonate]]s and the [[elderly]], with occasional systemic [[bacteremia]]. They can also colonize the intestines and the female reproductive tract, increasing the risk for premature rupture of membranes and transmission to the infant. The American College of Obstetricians and Gynecologists, American Academy of Pediatrics and the [[Centers for Disease Control]] recommend all pregnant women between 35 and 37 weeks gestation should be tested for GBS. Women who test positive should be given prophylactic antibiotics during labor, which will usually prevent transmission to the infant.<ref name=Schrag_2002>{{cite journal |author=Schrag S, Gorwitz R, Fultz-Butts K, Schuchat A |title=Prevention of perinatal group B streptococcal disease. Revised guidelines from CDC |journal=MMWR Recomm Rep |volume=51 |issue=RR-11 |pages=1–22 |year=2002 |pmid=12211284}}</ref> In the [[United Kingdom|UK]], clinicians have been slow to implement the same standards as the [[United States of America|US]], [[Australia]] and [[Canada]]. In the UK, only 1% of maternity units test for the presence of Group B Strep.<ref name=RCOG_2003>{{cite paper | author = Hughes, RG, et al. | title = Prevention of Early Onset Neonatal Group B Streptococcal Disease | publisher = Royal College of Obstetricians and Gynaecologists | url = http://www.rcog.org.uk/index.asp?PageID=520 | format = [[HTML]]}}</ref> Although The Royal College of Obstetricians and Gynaecologists issued risk-based guidelines in 2003 (due for review 2006), the implentation of these guidelines has been patchy. Some groups feel that as a result over 75 infants in the UK die each year of GBS related disease and another 600 or so suffer serious infection, most of which could be prevented <ref name=GBSS_2007>{{cite web | title = Group B Strep Support Home Page | publisher = Group B Strep Support | date = 2007-01-09 | url = http://www.gbss.org.uk/ | format = [[HTML]]}}</ref> however this is yet to be substantiated by RCT in the UK setting and, given the evidence for the efficacy of testing and treating from other countries, it may be that the large-scale trial necessary would receive neither funding nor ethics approval.<ref name=Arjb1_2007>{{cite web | title = RCOG: Preventing group B streptococcus infection in new born babies | publisher = RCOG | date = 2006-02 | url = http://www.rcog.org.uk/index.asp?PageID=1400#national | format = [[HTML]]}}</ref>


The invasive infections caused by group A beta-hemolytic streptococci tend to be more severe and less common. This occurs when the bacterium is able to infect areas where it is not usually found, such as the [[blood]] and [[Organ (anatomy)|organ]]s.<ref>{{cite web|title=Streptococcal Infections (Invasive Group A Strep)|url=http://www.nyc.gov/html/doh/html/cd/cdstrep.shtml|publisher=New York City Department of Health and Mental Hygiene|access-date=21 November 2012|archive-date=6 November 2012|archive-url=https://web.archive.org/web/20121106194414/http://www.nyc.gov/html/doh///html/cd/cdstrep.shtml|url-status=dead}}</ref> The diseases that may be caused include streptococcal [[toxic shock syndrome]], [[necrotizing fasciitis]], [[pneumonia]], and [[bacteremia]].<ref name="Cohen-Poradosu 2007"/> Globally, GAS has been estimated to cause more than 500,000 deaths every year, making it one of the world's leading [[pathogen]]s.<ref name="Cohen-Poradosu 2007"/>
====Group C ====
Includes ''S. equi'', which causes [[strangles]] in horses,<ref name=Harrington_2002>{{cite journal |author=Harrington D, Sutcliffe I, Chanter N |title=The molecular basis of Streptococcus equi infection and disease |journal=Microbes Infect |volume=4 |issue=4 |pages=501–10 |year=2002 |pmid=11932201 | doi = 10.1016/S1286-4579(02)01565-4 <!--Retrieved from CrossRef by DOI bot-->}}</ref> and ''[[Streptococcus zooepidemicus|S. zooepidemicus]]'', which causes infections in several species of mammals including cattle and horses. This can also cause death in chickens and [[moose]]. Many mountaineers from Canada have found corpses of moose lying in the middle of the road; post-mortem tests have found group c streptococcus in their blood.


Additional complications may be caused by GAS, namely acute [[rheumatic fever]] and acute [[glomerulonephritis]]. [[Rheumatic fever]], a disease that affects the [[joints]], [[kidneys]], and [[heart valves]], is a consequence of untreated strep A infection caused not by the bacterium itself, but due to the antibodies created by the immune system to fight off the infection cross-reacting with other proteins in the body. This "cross-reaction" causes the body to essentially attack itself and leads to the damage above. A similar autoimmune mechanism initiated by [[Group A streptococcal infection|Group A beta-hemolytic streptococcal (GABHS) infection]] is hypothesized to cause [[PANDAS (disorder)|pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS)]], wherein autoimmune antibodies affect the basal ganglia, causing rapid onset of psychiatric, motor, sleep, and other symptoms in pediatric patients.
====Group D (Enterococci) *variable in hemolysis====
Many former Group D streptococci have been reclassified and placed in the genus ''[[Enterococcus]]'' (includes ''S. faecalis'', ''S. faecium'', ''S. durans'', and ''S. avium'').<ref name=Ruoff_1990>{{cite journal | author=Ruoff KL | title=Recent taxonomic changes in the genus Enterococcus | journal=Eur J Clin Microbiol Infect Dis | year=1990 | pages=75–9 | volume=9 | issue=2 | pmid= 2108030 | doi = 10.1007/BF01963630 <!--Retrieved from CrossRef by DOI bot-->}}</ref> For example, ''Streptococcus faecalis'' is now ''[[Enterococcus faecalis]]''.


GAS infection is generally diagnosed with a [[rapid strep test]] or by culture.
The remaining non-enterococcal Group D strains include ''[[Streptococcus bovis]]'' and ''[[Streptococcus equinus]]''.


===Non-Hemolytic Streptococci===
==== Group B ====
''[[Streptococcus agalactiae|S. agalactiae]]'', or group B ''streptococcus'', '''GBS''', causes pneumonia and meningitis in [[Infant|newborns]] and the [[elderly]], with occasional systemic [[bacteremia]]. Importantly, ''Streptococcus agalactiae'' is the most common cause of meningitis in [[infant]]s from one month to three months old. They can also colonize the intestines and the female reproductive tract, increasing the risk for premature [[rupture of membranes]] during pregnancy, and [[vertically transmitted infection|transmission]] of the organism to the infant. The [[American College of Obstetricians and Gynecologists]], [[American Academy of Pediatrics]], and the [[Centers for Disease Control]] recommend all pregnant women between 35 and 37 weeks gestation to be tested for GBS. Women who test positive should be given prophylactic antibiotics during labor, which will usually prevent transmission to the infant.<ref name=Schrag_2002>{{cite journal | vauthors = Schrag S, Gorwitz R, Fultz-Butts K, Schuchat A | title = Prevention of perinatal group B streptococcal disease. Revised guidelines from CDC | journal = MMWR. Recommendations and Reports | volume = 51 | issue = RR-11 | pages = 1–22 | date = August 2002 | pmid = 12211284 }}</ref> Group III polysaccharide vaccines have been proven effective in preventing the passing of GBS from mother to infant.<ref>{{Cite journal |last1=Noya |first1=Francisco J. D. |last2=Baker |first2=Carol J. |date=1992-03-01 |title=PREVENTION OF GROUP B STREPTOCOCCAL INFECTION |url=https://www.sciencedirect.com/science/article/pii/S0891552020304244 |journal=Infectious Disease Clinics of North America |volume=6 |issue=1 |pages=41–55 |doi=10.1016/S0891-5520(20)30424-4 |pmid=1578122 |issn=0891-5520}}</ref>


The United Kingdom has chosen to adopt a risk factor-based protocol, rather than the culture-based protocol followed in the US.<ref>{{cite journal | vauthors = | title = Prevention of Early-onset Neonatal Group B Streptococcal Disease: Green-top Guideline No. 36 | journal = BJOG | volume = 124 | issue = 12 | pages = e280–e305 | date = November 2017 | pmid = 28901693 | doi = 10.1111/1471-0528.14821 | doi-access = free }}</ref> Current guidelines state that if one or more of the following risk factors is present, then the woman should be treated with ''intrapartum'' antibiotics:
Non-hemolytic streptococci rarely cause disease. However, weakly hemolytic group D beta-hemolytic streptococci and ''[[Listeria monocytogenes]]'' should not be confused with non-hemolytic
* GBS [[bacteriuria]] during this pregnancy
streptococci.
* History of GBS disease in a previous infant
* Intrapartum fever (≥38&nbsp;°C)
* Preterm labour (<37 weeks)
* Prolonged rupture of membranes (>18 hours)
This protocol results in the administration of intrapartum antibiotics to 15–20% of pregnant women and the prevention of 65–70% of cases of early onset GBS sepsis.<ref>{{cite book | vauthors = Norwitz ER, Schorge JO |title=Obstetrics and Gynecology at a Glance |date=2013 |publisher=John Wiley & Sons, Ltd. |location=Chichester |isbn=978-1118341735 |edition=4th}}</ref>


==References==
==== Group C ====
This group includes ''S. equi'', which causes [[strangles]] in horses,<ref name=Harrington_2002>{{cite journal | vauthors = Harrington DJ, Sutcliffe IC, Chanter N | title = The molecular basis of Streptococcus equi infection and disease | journal = Microbes and Infection | volume = 4 | issue = 4 | pages = 501–510 | date = April 2002 | pmid = 11932201 | doi = 10.1016/S1286-4579(02)01565-4 | doi-access = free }}</ref> and ''[[Streptococcus zooepidemicus|S. zooepidemicus]]'' — ''[[Strangles|S. equi]]'' is a [[Clone (cell biology)|clonal]] descendant or [[biovar]] of the ancestral ''[[Streptococcus zooepidemicus|S. zooepidemicus]]'' — which causes infections in several species of mammals, including cattle and horses. ''[[Streptococcus dysgalactiae|S. dysgalactiae]] subsp. dysgalactiae''<ref name="Haslam_2023">{{cite book | vauthors = Haslam DB, St Geme III JW | chapter = 122 - Groups C and G Streptococci | pages = 752–753 | veditors = Long SS, Prober CG, Fischer M, Kimberlin D |title=Principles and Practice of Pediatric Infectious Diseases | date = 2023 | edition = Sixth |publisher=Elsevier | doi = 10.1016/B978-0-323-75608-2.00122-1 | isbn = 978-0-323-75608-2 }} Note that according to the same source, the subspecies ''equisimilis'' is a grouping of large ''S. dysgalactiae'' colonies, whether they are members of Group C or Group G.</ref> is also a member of group C, [[beta-haemolytic streptococci]] that can cause [[pharyngitis]] and other [[pyogenic]] infections similar to [[Group a streptococcus|group A streptococci]]. Group C streptococcal bacteria are considered zoonotic pathogens, meaning infection can be passed from animal to human.<ref>{{Cite journal |last=Klos |first=Marta |date=12 June 2017 |title=Pathogenicity of Virulent Species of Group C Streptococci in Human |journal=Can J Infect Dis Med Microbiol |volume=2017|pages=1–5 |doi=10.1155/2017/9509604 |doi-access=free |pmid=28694832 |pmc=5485279 }}</ref>

==== Group D (enterococci) ====
Many former group D streptococci have been reclassified and placed in the genus ''[[Enterococcus]]'' (including ''E. faecalis'', ''E. faecium'', ''E. durans'', and ''E. avium'').<ref name="pmid17400023">{{cite journal | vauthors = Köhler W | title = The present state of species within the genera Streptococcus and Enterococcus | journal = International Journal of Medical Microbiology | volume = 297 | issue = 3 | pages = 133–150 | date = June 2007 | pmid = 17400023 | doi = 10.1016/j.ijmm.2006.11.008 }}</ref> For example, ''Streptococcus faecalis'' is now ''[[Enterococcus faecalis]]''. ''E. faecalis'' is sometimes alpha-hemolytic and ''E. faecium'' is sometimes beta hemolytic.<ref>Holt et al. (1994). ''Bergey's Manual of Determinative Bacteriology'' (9th ed.). Lippincott Williams & Wilkins. {{ISBN|0-683-00603-7}}</ref>

The remaining nonenterococcal group D strains include ''[[Streptococcus gallolyticus]]'', ''[[Streptococcus bovis]]'', ''[[Streptococcus equinus]]'' and ''[[Streptococcus suis]]''.

Nonhemolytic streptococci rarely cause illness. However, weakly hemolytic group D beta-hemolytic streptococci and ''[[Listeria monocytogenes]]'' (which is actually a [[gram-positive]] bacillus) should not be confused with nonhemolytic streptococci.

====Group F streptococci====
Group F streptococci were first described in 1934 by Long and [[Eleanor Albert Bliss|Bliss]] among the "minute haemolytic streptococci".<ref name=Whitworth_1990>{{cite journal | vauthors = Whitworth JM | title = Lancefield group F and related streptococci | journal = Journal of Medical Microbiology | volume = 33 | issue = 3 | pages = 135–151 | date = November 1990 | pmid = 2250284 | doi = 10.1099/00222615-33-3-135 | doi-access = free }}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> They are also known as ''[[Streptococcus anginosus]]'' (according to the Lancefield classification system) or as members of the [[Streptococcus milleri group|''S. milleri'' group]] (according to the European system).

====Group G streptococci====
These streptococci are usually, but not exclusively, beta-hemolytic. ''[[Streptococcus dysgalactiae]] subsp. canis''<ref name="Haslam_2023" /> is the predominant subspecies encountered. It is a particularly common GGS in humans, although it is typically found on animals. ''S. phocae'' is a GGS subspecies that has been found in marine mammals and marine fish species. In marine mammals it has been mainly associated with [[meningoencephalitis]], [[sepsis]], and [[endocarditis]], but is also associated with many other pathologies. Its environmental reservoir and means of transmission in marine mammals is not well characterized. Group G streptococci are also considered zoonotic pathogens.

==== Group H streptococci ====
Group H streptococci cause infections in medium-sized canines. Group H streptococci rarely cause human illness unless a human has direct contact with the mouth of a canine. One of the most common ways this can be spread is human-to-canine, mouth-to-mouth contact. However, the canine may lick the human's hand and infection can be spread, as well.<ref>{{cite web |title=Bacterial Infection (Streptococcus) in Dogs |url=http://www.petmd.com/dog/conditions/respiratory/c_multi_streptococcal_infections |website=petmd.com |access-date=12 December 2014}}</ref>

== Clinical identification==
[[File:Diagnostic algorithm of possible bacterial infection.png|thumb|Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England setting. Main ''Streptococcus'' groups are included as "''Strep.''" at bottom left.]]
In clinical practice, the most common groups of ''Streptococcus'' can be distinguished by simple bench tests, such as the PYR test for [[group A streptococcus]]. There are also latex agglutination kits which can distinguish each of the main groups seen in clinical practice.

== Treatment ==
Streptococcal infections can be treated with antibiotics from the [[penicillin]] family. Most commonly, penicillin or amoxicillin is used to treat strep infection. These antibiotics work by disrupting peptidoglycan production in the cell wall.<ref>{{Cite journal |last=Lowe |first=Derek |date=19 Jan 2022 |title=How Do Penicillins Actually Work? |url=https://www.science.org/content/blog-post/how-do-penicillins-actually-work |journal=Science |via=American Association for the Advancement of Science}}</ref> Treatment most often occurs as a 10-day oral antibiotic cycle. For patients with penicillin allergies and those suffering from skin infections, clindamycin can be used. Clindamycin works by disrupting protein synthesis within the cell.

==Molecular taxonomy and phylogenetics==
[[File:Streptococcus phylogenetic tree.png|thumb|Phylogenetic tree of ''Streptococcus'' species, based on data from PATRIC.<ref>{{cite web |title=Bacteria-Firmicutes-Bacilli-Lactobacillales-Streptococcaceae-Streptococcus |url=https://www.patricbrc.org/view/Taxonomy/1301#view_tab=phylogeny |website=PATRIC, University of Chicago |access-date=12 December 2014}}</ref> 16S groups are indicated by brackets and their key members are highlighted in red.]]
Streptococci have been divided into six groups on the basis of their [[16S ribosomal RNA|16S]] rDNA sequences: ''S. anginosus, S. gallolyticus, S. mitis, S. mutans, S. pyogenes'' and ''S. salivarius''.<ref name=Kawamura1995>{{cite journal | vauthors = Kawamura Y, Hou XG, Sultana F, Miura H, Ezaki T | title = Determination of 16S rRNA sequences of Streptococcus mitis and Streptococcus gordonii and phylogenetic relationships among members of the genus Streptococcus | journal = International Journal of Systematic Bacteriology | volume = 45 | issue = 2 | pages = 406–408 | date = April 1995 | pmid = 7537076 | doi = 10.1099/00207713-45-2-406 | doi-access = free }}</ref> The 16S groups have been confirmed by whole genome sequencing (see figure). The important pathogens ''S. pneumoniae'' and ''S. pyogenes'' belong to the ''S. mitis'' and ''S. pyogenes'' groups, respectively,<ref>Liu, D., ''Molecular Detection of Human Bacterial Pathogens'' ([[Boca Raton, Florida|Boca Raton]]: [[CRC Press]], 2011), [https://books.google.com/books?id=nnGhc44bypAC&pg=PA324 p. 324].</ref> while the causative agent of [[dental caries]], ''[[Streptococcus mutans]]'', is basal to the ''Streptococcus'' group.
[[File:Streptococcus subclades.png|thumb|A conceptual diagram of ''Streptococcus'' subclade taxonomy based on phylogenetic trees and the [[conserved signature indels]] (CSIs) that are specifically shared by groups of streptococci.<ref name=":0"/> The number of CSIs identified for each group is shown. ]]
Recent technological advances have resulted in an increase of available genome sequences for ''Streptococcus'' species, allowing for more robust and reliable phylogenetic and comparative genomic analyses to be conducted.<ref name=":0">{{cite journal | vauthors = Patel S, Gupta RS | title = Robust demarcation of fourteen different species groups within the genus Streptococcus based on genome-based phylogenies and molecular signatures | journal = Infection, Genetics and Evolution | volume = 66 | pages = 130–151 | date = December 2018 | pmid = 30248475 | doi = 10.1016/j.meegid.2018.09.020 | bibcode = 2018InfGE..66..130P | s2cid = 52813184 }}</ref> In 2018, the evolutionary relationships within ''Streptococcus'' was re-examined by Patel and Gupta through the analysis of comprehensive [[phylogenetic tree]]s constructed based on four different datasets of proteins and the identification of 134 highly specific molecular signatures (in the form of [[conserved signature indels]]) that are exclusively shared by the entire genus or its distinct subclades.<ref name=":0" />

The results revealed the presence of two main clades at the highest level within ''Streptococcus'', termed the "Mitis-Suis" and "Pyogenes-Equinus-Mutans" clades.<ref name=":0" /> The "Mitis-Suis" main clade comprises the Suis subclade and the Mitis clade, which encompasses the Angiosus, Pneumoniae, Gordonii and Parasanguinis subclades. The second main clade, the "Pyogenes-Equinus-Mutans", includes the Pyogenes, Mutans, Salivarius, Equinus, Sobrinus, Halotolerans, Porci, Entericus and Orisratti subclades. In total, 14 distinct subclades have been identified within the genus ''Streptococcus'', each supported by reliable branching patterns in phylogenetic trees and by the presence of multiple [[conserved signature indels]] in different proteins that are distinctive characteristics of the members of these 14 clades.<ref name=":0" /> A summary diagram showing the overall relationships among the ''Streptococcus'' based on these studies is depicted in a figure on this page.

==Genomics==
[[File:Streptococcus gene overlap.png|thumb|Common and species-specific genes among ''[[Streptococcus sanguinis]]'', ''[[Streptococcus mutans|S. mutans]]'', and ''[[Streptococcus pneumoniae|S. pneumoniae]]''. Modified after Xu et al. (2007)<ref name="Xu2007">{{cite journal | vauthors = Xu P, Alves JM, Kitten T, Brown A, Chen Z, Ozaki LS, Manque P, Ge X, Serrano MG, Puiu D, Hendricks S, Wang Y, Chaplin MD, Akan D, Paik S, Peterson DL, Macrina FL, Buck GA | display-authors = 6 | title = Genome of the opportunistic pathogen Streptococcus sanguinis | journal = Journal of Bacteriology | volume = 189 | issue = 8 | pages = 3166–3175 | date = April 2007 | pmid = 17277061 | pmc = 1855836 | doi = 10.1128/JB.01808-06 }}</ref> ]]
The genomes of hundreds of species have been sequenced.<ref>{{cite web | url = http://patricbrc.org/portal/portal/patric/Taxon?cType=taxon&cId=1301 | title = Streptococcus | archive-url =https://web.archive.org/web/20130310052630/http://patricbrc.org/portal/portal/patric/Taxon?cType=taxon&cId=1301 | archive-date=2013-03-10 | work = PATRIC | publisher = Virginia Bioinformatics Institute | location = Blacksburg, VA }}</ref> Most ''Streptococcus'' genomes are 1.8 to 2.3 Mb in size and encode 1,700 to 2,300 proteins. Some important genomes are listed in the table.<ref name="Ferretti2004">{{cite journal | vauthors = Ferretti JJ, Ajdic D, McShan WM | title = Comparative genomics of streptococcal species | journal = The Indian Journal of Medical Research | volume = 119 | issue = Suppl | pages = 1–6 | date = May 2004 | pmid = 15232152 }}</ref> The four species shown in the table (''S. pyogenes, S. agalactiae, S. pneumoniae'', and ''S. mutans'') have an average pairwise protein sequence identity of about 70%.<ref name="Ferretti2004" />

{| class="wikitable"
!feature !! ''S. pyogenes'' !!''S. agalactiae''!!''S. pneumoniae''!! ''S. mutans''
|-
| [[base pair]]s || 1,852,442|| 2,211,488 ||2,160,837 ||2,030,921
|-
| [[Open reading frame|ORFs]] || 1792 ||2118 ||2236 ||1963
|-
| [[prophage]]s || yes ||no ||no ||no
|}

== Bacteriophage ==
[[Bacteriophage]]s have been described for many species of ''Streptococcus''. 18 [[prophage]]s have been described in ''[[Streptococcus pneumoniae|S. pneumoniae]]'' that range in size from 38 to 41 kb in size, encoding from 42 to 66 genes each.<ref>{{Citation |last1=McShan |first1=W. Michael |title=The Bacteriophages of Streptococcus pyogenes |date=2016 |work=Streptococcus pyogenes: Basic Biology to Clinical Manifestations |editor-last=Ferretti |editor-first=Joseph J. |url=http://www.ncbi.nlm.nih.gov/books/NBK333409/ |access-date=2024-02-07 |place=Oklahoma City (OK) |publisher=University of Oklahoma Health Sciences Center |pmid=26866212 |last2=Nguyen |first2=Scott V. |editor2-last=Stevens |editor2-first=Dennis L. |editor3-last=Fischetti |editor3-first=Vincent A.}}</ref> Some of the first ''Streptococcus'' phages discovered were Dp-1<ref>
McDonnell M, Ronda C, Tomasz A (1975) "Diplophage": a bacteriophage of Diplococcus pneumoniae. Virology 63:577–582</ref><ref>NCBI: [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Undef&id=59241 Streptococcus phage Dp-1] (species)</ref>
and ω1 (alias ω-1).<!--neither ICTV nor NCBI Tax Browser. 2020-06-17 --><ref>Tiraby JG, Tiraby E, Fox MS (Dec 1975) Pneumococcal bacteriophages. Virology 68:566–569. [[doi:10.1016/0042-6822(75)90300-1]]. {{PMID|844}}</ref><ref name="pmid15492930">{{cite journal | vauthors = López R | title = Streptococcus pneumoniae and its bacteriophages: one long argument | journal = International Microbiology | volume = 7 | issue = 3 | pages = 163–171 | date = September 2004 | pmid = 15492930 }} [https://web.archive.org/web/20170809143835/http://www.im.microbios.org/0703/0703163.pdf PDF via web archive] (9 Aug 2017)</ref><ref>Rubens López, Ernesto García: [https://academic.oup.com/femsre/article/28/5/553/776721 Recent trends on the molecular biology of pneumococcal capsules, lytic enzymes, and bacteriophage], Oxford Academic FEMS Microbiology Reviews. Volume 28, Issue 5. 1 Nov 2004, pp.&nbsp;554—580, [[doi:10.1016/j.femsre.2004.05.002]] (Free Fulltext)</ref>
In 1981 the Cp (Complutense phage 1, officially ''Streptococcus virus Cp1'', ''[[Picovirinae]]'') family was discovered with Cp-1 as its first member.<ref name="pmid6275103">{{cite journal | vauthors = Ronda C, López R, García E | title = Isolation and characterization of a new bacteriophage, Cp-1, infecting Streptococcus pneumoniae | journal = Journal of Virology | volume = 40 | issue = 2 | pages = 551–559 | date = November 1981 | pmid = 6275103 | pmc = 256658 | doi = 10.1128/JVI.40.2.551-559.1981 }}</ref> Dp-1 and Cp-1 infect both ''S. pneumoniae'' and ''[[Streptococcus mitis|S. mitis]]''.<ref name="pmid25692983">{{cite journal | vauthors = Ouennane S, Leprohon P, Moineau S | title = Diverse virulent pneumophages infect Streptococcus mitis | journal = PLOS ONE | volume = 10 | issue = 2 | pages = e0118807 | year = 2015 | pmid = 25692983 | pmc = 4334900 | doi = 10.1371/journal.pone.0118807 | doi-access = free | bibcode = 2015PLoSO..1018807O }}</ref> However, the host ranges of most ''Streptococcus'' phages have not been investigated systematically.

==Natural genetic transformation==

[[Transformation (genetics)|Natural genetic transformation]] involves the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a complex process dependent on the expression of numerous genes. To be capable of transformation a bacterium must enter a special physiologic state referred to as [[Natural competence|competence]]. [[Streptococcus pneumoniae|''S. pneumoniae'']], [[Streptococcus mitis|''S. mitis'']] and [[Streptococcus oralis|''S. oralis'']] can become competent, and as a result actively acquire homologous DNA for transformation by a predatory fratricidal mechanism <ref name="pmid18485065">{{cite journal | vauthors = Johnsborg O, Eldholm V, Bjørnstad ML, Håvarstein LS | title = A predatory mechanism dramatically increases the efficiency of lateral gene transfer in Streptococcus pneumoniae and related commensal species | journal = Molecular Microbiology | volume = 69 | issue = 1 | pages = 245–253 | date = July 2008 | pmid = 18485065 | doi = 10.1111/j.1365-2958.2008.06288.x | s2cid = 30923996 | doi-access = free }}</ref> This fratricidal mechanism mainly exploits non-competent siblings present in the same niche <ref name="pmid17277796">{{cite journal | vauthors = Claverys JP, Håvarstein LS | title = Cannibalism and fratricide: mechanisms and raisons d'être | journal = Nature Reviews. Microbiology | volume = 5 | issue = 3 | pages = 219–229 | date = March 2007 | pmid = 17277796 | doi = 10.1038/nrmicro1613 | s2cid = 35433490 }}</ref> Among highly competent isolates of ''S. pneumoniae'', Li et al.<ref name="pmid27068094">{{cite journal | vauthors = Li G, Liang Z, Wang X, Yang Y, Shao Z, Li M, Ma Y, Qu F, Morrison DA, Zhang JR | display-authors = 6 | title = Addiction of Hypertransformable Pneumococcal Isolates to Natural Transformation for In Vivo Fitness and Virulence | journal = Infection and Immunity | volume = 84 | issue = 6 | pages = 1887–1901 | date = June 2016 | pmid = 27068094 | pmc = 4907133 | doi = 10.1128/IAI.00097-16 }}</ref> showed that nasal colonization fitness and virulence (lung infectivity) depend on an intact competence system. Competence may allow the streptococcal pathogen to use external homologous DNA for recombinational repair of DNA damages caused by the host's oxidative attack.<ref name="pmid18295550">{{cite journal | vauthors = Michod RE, Bernstein H, Nedelcu AM | title = Adaptive value of sex in microbial pathogens | journal = Infection, Genetics and Evolution | volume = 8 | issue = 3 | pages = 267–285 | date = May 2008 | pmid = 18295550 | doi = 10.1016/j.meegid.2008.01.002 | bibcode = 2008InfGE...8..267M }}</ref>

== See also ==
* [[Cia-dependent small RNAs]]
* [[Quellung reaction]]
* [[Streptococcal infection in poultry]]
* [[Streptococcal pharyngitis]]
* [[Streptokinase]]

== References ==
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==External links==
== External links ==
* {{cite journal | title = Adoption of perinatal group B streptococcal disease prevention recommendations by prenatal-care providers--Connecticut and Minnesota, 1998 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 49 | issue = 11 | pages = 228–232 | date = March 2000 | pmid = 10763673 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5111a1.htm | author1 = Centers for Disease Control and Prevention (CDC) }}
*[http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5111a1.htm Prevention of Perinatal Group B Streptococcal Disease] August 16, 2002 MMWR 2000;49:228-232.
* [https://scitechdaily.com/nature-inspired-crispr-enzyme-discoveries-vastly-expand-genome-editing/ Nature-Inspired CRISPR Enzyme Discoveries Vastly Expand Genome Editing ]. On: SciTechDaily. June 16, 2020. Source: Media Lab, Massachusetts Institute of Technology.
*[http://www.strepb.ca/home.htm The Canadian Strep B Foundation]
* [https://patricbrc.org/view/Taxonomy/1301#view_tab=overview Streptococcus] genomes and related information at [http://patricbrc.org/ PATRIC], a Bioinformatics Resource Center funded by [https://www.niaid.nih.gov/ NIAID]
*[http://www.gbss.org.uk The UK Group B Strep Support charity]
* [http://www.strepb.ca/home.htm The Canadian Strep B Foundation] {{Webarchive|url=https://web.archive.org/web/20130502151359/http://www.strepb.ca/home.htm |date=2013-05-02 }}
* [http://www.gbss.org.uk The UK Group B Strep Support] charity
* Stuttering [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7693426/ Streptococcal Infection] Infection


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[[Category:Streptococcaceae]]
[[Category:Streptococcaceae]]
[[Category:Gut flora]]
[[Category:Gut flora bacteria]]
[[Category:Gram-positive bacteria]]

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[[es:Streptococcus]]
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Latest revision as of 15:20, 15 November 2024

Not to be confused with Staphylococcus.
See also: Strep throat

Streptococcus
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Bacillota
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Rosenbach, 1884
Species[1]

Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota.[2] 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),[3] by combining the prefix "strepto-" (from Ancient Greek: στρεπτός, romanized: streptós, lit. 'easily twisted, pliant'[4]), together with the suffix "-coccus" (from Modern Latin: coccus, from Ancient Greek: κόκκος, romanized: kókkos, lit. 'grain, seed, berry'.[5]) In 1984, many bacteria formerly grouped in the genus Streptococcus were separated out into the genera Enterococcus and Lactococcus.[6] Currently, over 50 species are recognised in this genus. This genus has been found to be part of the salivary microbiome.[7]

Pathogenesis and classification

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See also: Streptococcosis

In addition to streptococcal pharyngitis (strep throat), certain Streptococcus species are responsible for many cases of pink eye,[8] meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis (the 'flesh-eating' bacterial infections). However, many streptococcal species are not pathogenic, and form part of the commensal human microbiota of the mouth, skin, intestine, and upper respiratory tract. Streptococci are also a necessary ingredient in producing Emmentaler ("Swiss") cheese.[9]

Species of streptococci are classified based on their hemolytic properties.[10] Alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Beta-hemolytic species cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. Gamma-hemolytic species cause no hemolysis.[11]

Beta-hemolytic streptococci are further classified by Lancefield grouping, a serotype classification (that is, describing specific carbohydrates present on the bacterial cell wall).[6] The 21 described serotypes are named Lancefield groups A to W (excluding E, I and J). This system of classification was developed by Rebecca Lancefield, a scientist at Rockefeller University.[12]

In the medical setting, the most important groups are the alpha-hemolytic streptococci S. pneumoniae and Streptococcus viridans groups, and the beta-hemolytic streptococci of Lancefield groups A and B (also known as "group A strep" and "group B strep").

Table: Medically relevant streptococci[10]

Species Host Disease
S. pyogenes human pharyngitis, cellulitis, erysipelas
S. agalactiae human, cattle neonatal meningitis and sepsis
S. dysgalactiae human, animals endocarditis, bacteremia, pneumonia, meningitis, respiratory infections
S. gallolyticus human, animals biliary or urinary tract infections, endocarditis
S. anginosus human, animals subcutaneous/organ abscesses, meningitis, respiratory infections
S. sanguinis human endocarditis, dental caries
S. suis swine meningitis
S. mitis human endocarditis
S. mutans human dental caries
S. pneumoniae human pneumonia

Alpha-hemolytic

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When alpha-hemolysis (α-hemolysis) is present, the agar under the colony will appear dark and greenish due to the conversion of hemoglobin to green biliverdin. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha-hemolysis. Alpha-hemolysis is also termed incomplete hemolysis or partial hemolysis because the cell membranes of the red blood cells are left intact. This is also sometimes called green hemolysis because of the color change in the agar.[citation needed]

Pneumococci

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  • S. pneumoniae (sometimes called pneumococcus), is a leading cause of bacterial pneumonia and the occasional etiology of otitis media, sinusitis, meningitis, and peritonitis. Inflammation is thought to be the major cause of how pneumococci cause disease, hence the tendency of diagnoses associated with them to involve inflammation. They possess no Lancefield antigens.[2]

The viridans group: alpha-hemolytic

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Beta-hemolytic

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Beta-hemolysis (β-hemolysis), sometimes called complete hemolysis, is a complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells. There are two types of streptolysin: Streptolysin O (SLO) and streptolysin S (SLS). Streptolysin O is an oxygen-sensitive cytotoxin, secreted by most group A Streptococcus (GAS), and interacts with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), and usually results in beta-hemolysis under the surface of blood agar. Streptolysin S is an oxygen-stable cytotoxin also produced by most GAS strains which results in clearing on the surface of blood agar. SLS affects immune cells, including polymorphonuclear leukocytes and lymphocytes, and is thought to prevent the host immune system from clearing infection. Streptococcus pyogenes, or GAS, displays beta hemolysis.

Some weakly beta-hemolytic species cause intense hemolysis when grown together with a strain of Staphylococcus. This is called the CAMP test. Streptococcus agalactiae displays this property. Clostridium perfringens can be identified presumptively with this test. Listeria monocytogenes is also positive on sheep's blood agar.

Alpha-hemolytic S. viridans (right) and beta-hemolytic S. pyogenes (left) streptococci growing on blood agar

Group A

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Group A S. pyogenes is the causative agent in a wide range of group A streptococcal infections (GAS). These infections may be noninvasive or invasive. The noninvasive infections tend to be more common and less severe. The most common of these infections include streptococcal pharyngitis (strep throat) and impetigo.[13] Scarlet fever is another example of Group A noninvasive infection.

The invasive infections caused by group A beta-hemolytic streptococci tend to be more severe and less common. This occurs when the bacterium is able to infect areas where it is not usually found, such as the blood and organs.[14] The diseases that may be caused include streptococcal toxic shock syndrome, necrotizing fasciitis, pneumonia, and bacteremia.[13] Globally, GAS has been estimated to cause more than 500,000 deaths every year, making it one of the world's leading pathogens.[13]

Additional complications may be caused by GAS, namely acute rheumatic fever and acute glomerulonephritis. Rheumatic fever, a disease that affects the joints, kidneys, and heart valves, is a consequence of untreated strep A infection caused not by the bacterium itself, but due to the antibodies created by the immune system to fight off the infection cross-reacting with other proteins in the body. This "cross-reaction" causes the body to essentially attack itself and leads to the damage above. A similar autoimmune mechanism initiated by Group A beta-hemolytic streptococcal (GABHS) infection is hypothesized to cause pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS), wherein autoimmune antibodies affect the basal ganglia, causing rapid onset of psychiatric, motor, sleep, and other symptoms in pediatric patients.

GAS infection is generally diagnosed with a rapid strep test or by culture.

Group B

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S. agalactiae, or group B streptococcus, GBS, causes pneumonia and meningitis in newborns and the elderly, with occasional systemic bacteremia. Importantly, Streptococcus agalactiae is the most common cause of meningitis in infants from one month to three months old. They can also colonize the intestines and the female reproductive tract, increasing the risk for premature rupture of membranes during pregnancy, and transmission of the organism to the infant. The American College of Obstetricians and Gynecologists, American Academy of Pediatrics, and the Centers for Disease Control recommend all pregnant women between 35 and 37 weeks gestation to be tested for GBS. Women who test positive should be given prophylactic antibiotics during labor, which will usually prevent transmission to the infant.[15] Group III polysaccharide vaccines have been proven effective in preventing the passing of GBS from mother to infant.[16]

The United Kingdom has chosen to adopt a risk factor-based protocol, rather than the culture-based protocol followed in the US.[17] Current guidelines state that if one or more of the following risk factors is present, then the woman should be treated with intrapartum antibiotics:

  • GBS bacteriuria during this pregnancy
  • History of GBS disease in a previous infant
  • Intrapartum fever (≥38 °C)
  • Preterm labour (<37 weeks)
  • Prolonged rupture of membranes (>18 hours)

This protocol results in the administration of intrapartum antibiotics to 15–20% of pregnant women and the prevention of 65–70% of cases of early onset GBS sepsis.[18]

Group C

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This group includes S. equi, which causes strangles in horses,[19] and S. zooepidemicus — S. equi is a clonal descendant or biovar of the ancestral S. zooepidemicus — which causes infections in several species of mammals, including cattle and horses. S. dysgalactiae subsp. dysgalactiae[20] is also a member of group C, beta-haemolytic streptococci that can cause pharyngitis and other pyogenic infections similar to group A streptococci. Group C streptococcal bacteria are considered zoonotic pathogens, meaning infection can be passed from animal to human.[21]

Group D (enterococci)

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Many former group D streptococci have been reclassified and placed in the genus Enterococcus (including E. faecalis, E. faecium, E. durans, and E. avium).[22] For example, Streptococcus faecalis is now Enterococcus faecalis. E. faecalis is sometimes alpha-hemolytic and E. faecium is sometimes beta hemolytic.[23]

The remaining nonenterococcal group D strains include Streptococcus gallolyticus, Streptococcus bovis, Streptococcus equinus and Streptococcus suis.

Nonhemolytic streptococci rarely cause illness. However, weakly hemolytic group D beta-hemolytic streptococci and Listeria monocytogenes (which is actually a gram-positive bacillus) should not be confused with nonhemolytic streptococci.

Group F streptococci

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Group F streptococci were first described in 1934 by Long and Bliss among the "minute haemolytic streptococci".[24] They are also known as Streptococcus anginosus (according to the Lancefield classification system) or as members of the S. milleri group (according to the European system).

Group G streptococci

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These streptococci are usually, but not exclusively, beta-hemolytic. Streptococcus dysgalactiae subsp. canis[20] is the predominant subspecies encountered. It is a particularly common GGS in humans, although it is typically found on animals. S. phocae is a GGS subspecies that has been found in marine mammals and marine fish species. In marine mammals it has been mainly associated with meningoencephalitis, sepsis, and endocarditis, but is also associated with many other pathologies. Its environmental reservoir and means of transmission in marine mammals is not well characterized. Group G streptococci are also considered zoonotic pathogens.

Group H streptococci

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Group H streptococci cause infections in medium-sized canines. Group H streptococci rarely cause human illness unless a human has direct contact with the mouth of a canine. One of the most common ways this can be spread is human-to-canine, mouth-to-mouth contact. However, the canine may lick the human's hand and infection can be spread, as well.[25]

Clinical identification

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Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England setting. Main Streptococcus groups are included as "Strep." at bottom left.

In clinical practice, the most common groups of Streptococcus can be distinguished by simple bench tests, such as the PYR test for group A streptococcus. There are also latex agglutination kits which can distinguish each of the main groups seen in clinical practice.

Treatment

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Streptococcal infections can be treated with antibiotics from the penicillin family. Most commonly, penicillin or amoxicillin is used to treat strep infection. These antibiotics work by disrupting peptidoglycan production in the cell wall.[26] Treatment most often occurs as a 10-day oral antibiotic cycle. For patients with penicillin allergies and those suffering from skin infections, clindamycin can be used. Clindamycin works by disrupting protein synthesis within the cell.

Molecular taxonomy and phylogenetics

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Phylogenetic tree of Streptococcus species, based on data from PATRIC.[27] 16S groups are indicated by brackets and their key members are highlighted in red.

Streptococci have been divided into six groups on the basis of their 16S rDNA sequences: S. anginosus, S. gallolyticus, S. mitis, S. mutans, S. pyogenes and S. salivarius.[28] The 16S groups have been confirmed by whole genome sequencing (see figure). The important pathogens S. pneumoniae and S. pyogenes belong to the S. mitis and S. pyogenes groups, respectively,[29] while the causative agent of dental caries, Streptococcus mutans, is basal to the Streptococcus group.

A conceptual diagram of Streptococcus subclade taxonomy based on phylogenetic trees and the conserved signature indels (CSIs) that are specifically shared by groups of streptococci.[30] The number of CSIs identified for each group is shown.

Recent technological advances have resulted in an increase of available genome sequences for Streptococcus species, allowing for more robust and reliable phylogenetic and comparative genomic analyses to be conducted.[30] In 2018, the evolutionary relationships within Streptococcus was re-examined by Patel and Gupta through the analysis of comprehensive phylogenetic trees constructed based on four different datasets of proteins and the identification of 134 highly specific molecular signatures (in the form of conserved signature indels) that are exclusively shared by the entire genus or its distinct subclades.[30]

The results revealed the presence of two main clades at the highest level within Streptococcus, termed the "Mitis-Suis" and "Pyogenes-Equinus-Mutans" clades.[30] The "Mitis-Suis" main clade comprises the Suis subclade and the Mitis clade, which encompasses the Angiosus, Pneumoniae, Gordonii and Parasanguinis subclades. The second main clade, the "Pyogenes-Equinus-Mutans", includes the Pyogenes, Mutans, Salivarius, Equinus, Sobrinus, Halotolerans, Porci, Entericus and Orisratti subclades. In total, 14 distinct subclades have been identified within the genus Streptococcus, each supported by reliable branching patterns in phylogenetic trees and by the presence of multiple conserved signature indels in different proteins that are distinctive characteristics of the members of these 14 clades.[30] A summary diagram showing the overall relationships among the Streptococcus based on these studies is depicted in a figure on this page.

Genomics

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Common and species-specific genes among Streptococcus sanguinis, S. mutans, and S. pneumoniae. Modified after Xu et al. (2007)[31]

The genomes of hundreds of species have been sequenced.[32] Most Streptococcus genomes are 1.8 to 2.3 Mb in size and encode 1,700 to 2,300 proteins. Some important genomes are listed in the table.[33] The four species shown in the table (S. pyogenes, S. agalactiae, S. pneumoniae, and S. mutans) have an average pairwise protein sequence identity of about 70%.[33]

feature S. pyogenes S. agalactiae S. pneumoniae S. mutans
base pairs 1,852,442 2,211,488 2,160,837 2,030,921
ORFs 1792 2118 2236 1963
prophages yes no no no

Bacteriophage

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Bacteriophages have been described for many species of Streptococcus. 18 prophages have been described in S. pneumoniae that range in size from 38 to 41 kb in size, encoding from 42 to 66 genes each.[34] Some of the first Streptococcus phages discovered were Dp-1[35][36] and ω1 (alias ω-1).[37][38][39] In 1981 the Cp (Complutense phage 1, officially Streptococcus virus Cp1, Picovirinae) family was discovered with Cp-1 as its first member.[40] Dp-1 and Cp-1 infect both S. pneumoniae and S. mitis.[41] However, the host ranges of most Streptococcus phages have not been investigated systematically.

Natural genetic transformation

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Natural genetic transformation involves the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a complex process dependent on the expression of numerous genes. To be capable of transformation a bacterium must enter a special physiologic state referred to as competence. S. pneumoniae, S. mitis and S. oralis can become competent, and as a result actively acquire homologous DNA for transformation by a predatory fratricidal mechanism [42] This fratricidal mechanism mainly exploits non-competent siblings present in the same niche [43] Among highly competent isolates of S. pneumoniae, Li et al.[44] showed that nasal colonization fitness and virulence (lung infectivity) depend on an intact competence system. Competence may allow the streptococcal pathogen to use external homologous DNA for recombinational repair of DNA damages caused by the host's oxidative attack.[45]

See also

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References

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  2. ^ a b c Ryan KJ, Sherris JC, eds. (1994). Sherris Medical Microbiology (3rd ed.). Appleton & Lange. pp. 266–7. ISBN 0-8385-8541-8.
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  4. ^ στρεπτός in Liddell, Henry George; Scott, Robert (1940) A Greek–English Lexicon, revised and augmented throughout by Jones, Sir Henry Stuart, with the assistance of McKenzie, Roderick. Oxford: Clarendon Press. In the Perseus Digital Library, Tufts University.
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