Editing Streptococcus (section)

==Pathogenesis and classification==
{{see also|Streptococcosis}}
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>

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>

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}}

====Pneumococci====
* ''[[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" />

====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>

=== 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.

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.
[[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 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.

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"/>

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.

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

==== 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:
* GBS [[bacteriuria]] during this pregnancy
* 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>

==== 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 }}</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>