Streptococcus pyogenes
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{{Taxobox
| color = lightblue
| name = ''Streptococcus pyogenes''
| image = Streptococcus_pyogenes_01.jpg
| image_width = 240px
| image_caption = ''S. pyogenes'' bacteria @ 900x magnification.
| regnum = [[Bacterium|Bacteria]]
| phylum = [[Firmicutes]]
| classis = [[Bacilli]]
| ordo = [[Lactobacillales]]
| familia = [[Streptococcaceae]]
| genus = ''[[Streptococcus]]''
| species = '''''S. pyogenes'''''
| binomial = ''Streptococcus pyogenes''
| binomial_authority = Rosenbach 1884
}}
'''''Streptococcus pyogenes''''' is a [[coccus|spherical]] [[gram-positive]] [[bacteria]] that grows in long chains <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 is the cause of [[Group A streptococcal infection]]s. ''S. pyogenes'' displays [[group A antigen]] on its cell wall and [[Hemolysis (microbiology)|beta-hemolysis]] when cultured on blood agar plate. ''S. pyogenes'' typically produces large zones of beta-hemolysis, the complete disruption of [[erythrocyte]]s and the release of [[hemoglobin]], and it is therefore called Group A (beta-hemolytic) ''[[Streptococcus]]'' (abbreviated ''GAS''). Streptococci are catalase-negative. In ideal conditions, Streptococcus pyogenes has an incubation period of approximately 10 days.
==Serotyping==
In 1928, [[Rebecca Lancefield]] published a method for serotyping ''S. pyogenes'' based on its ''M protein'', a [[virulence]] factor that is displayed on its surface.<ref name=Lancefield_1928>{{cite journal | author = Lancefield RC| title = The antigenic complex of ''Streptococcus hemolyticus'' | journal = J Exp Med | year = 1928 | volume = 47 | pages = 9–10 | url=http://www.jem.org/cgi/content/abstract/47/1/91| doi = 10.1084/jem.47.1.91 }}</ref> Later in 1946, Lancefield described the serologic classification of ''S. pyogenes'' isolates based on their surface ''T antigen''.<ref name=Lancefield_1946>{{cite journal | author = Lancefield RC, Dole VP | title = The properties of T antigen extracted from group A hemolytic streptococci | journal = J Exp Med | year = 1946 | volume = 84 | pages = 449–71 | doi= 10.1084/jem.84.5.449 }}</ref> Four of the 20 T antigens have been revealed to be [[pilus|pili]], which are used by bacteria to attach to host cells.<ref name=Mora_2005>{{cite journal |author=Mora M, Bensi G, Capo S, Falugi F, Zingaretti C, Manetti A, Maggi T, Taddei A, Grandi G, Telford J |title=Group A Streptococcus produce pilus-like structures containing protective antigens and Lancefield T antigens |journal=Proc Natl Acad Sci U S A |volume=102 |issue=43 |pages=15641–6 |year=2005 |pmid=16223875 |doi=10.1073/pnas.0507808102}}</ref> Currently, over 100 M serotypes and approximately 20 T serotypes are known.
==Pathogenesis==
{{main|Group A streptococcal infection}}
''S. pyogenes'' is the cause of many important human diseases ranging from mild superficial skin infections to life-threatening systemic diseases. Infections typically begin in the throat or skin. Examples of mild ''S. pyogenes'' infections include [[pharyngitis]] ("strep throat") and localized skin infection ("[[impetigo]]"). [[Erysipelas]] and [[cellulitis]] are characterized by multiplication and lateral spread of ''S. pyogenes'' in deep layers of the skin. ''S. pyogenes'' invasion and multiplication in the [[fascia]] can lead to [[necrotizing fasciitis]], a potentially life-threatening condition requiring surgical treatment.
Infections due to certain strains of ''S. pyogenes'' can be associated with the release of bacterial [[toxin|toxins]]. Throat infections associated with release of certain toxins lead to [[scarlet fever]]. Other toxigenic ''S. pyogenes'' infections may lead to streptococcal [[toxic shock syndrome]], which can be life-threatening.
''S. pyogenes'' can also cause disease in the form of post-infectious "non-pyogenic" (not associated with local bacterial multiplication and pus formation) syndromes. These [[autoimmune]] mediated complications follow a small percentage of infections and include [[rheumatic fever]] and acute poststreptococcal [[glomerulonephritis]]. Both conditions appear several weeks following the initial streptococcal infection. [[Rheumatic fever]] is characterised by inflammation of the joints and/or heart following an episode of Streptococcal [[pharyngitis]]. Acute [[glomerulonephritis]], inflammation of the [[kidney|renal]] [[glomerulus]], can follow Streptococcal [[pharyngitis]] or skin infection.
This bacterium remains acutely sensitive to [[penicillin]]. Failure of treatment with [[penicillin]] is generally attributed to other local commensal organisms producing β-lactamase or failure to achieve adequate tissue levels in the pharynx. Certain strains have developed resistance to [[macrolides]], [[tetracyclines]] and [[clindamycin]].
==Virulence factors==
''S. pyogenes'' has several [[virulence]] factors that enable it to attach to host tissues, evade the immune response, and spread by penetrating host tissue layers.<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> A [[carbohydrate]] capsule composed of [[hyaluronic acid]] surrounds the bacterium, protecting it from [[phagocytosis]] by [[neutrophils]]. In addition, the capsule and several factors embedded in the cell wall, including M protein, [[lipoteichoic acid]], and protein F (SfbI) facilitate attachment to various host cells.<ref name=Bisno_2003>{{cite journal | author=Bisno AL, Brito MO, Collins CM | title=Molecular basis of group A streptococcal virulence | journal=Lancet Infect Dis | year=2003 | pages=191–200 | volume=3 | issue=4 | pmid=12679262 | doi=10.1016/S1473-3099(03)00576-0}}</ref> M protein also inhibits [[opsonization]] by the alternative [[complement system|complement pathway]] by binding to host complement regulators. M protein found on some serotypes are also able to prevent opsonization by binding to [[fibrinogen]]. However, the M protein is also the weakest point in this pathogen's defense as [[Antibody|antibodies]] produced by the [[immune system]] against M protein target the bacteria for engulfment by [[phagocytes]]. M proteins are unique to each strain, and identification can be used clinically to confirm the strain causing an infection.
''S. pyogenes'' releases a number of proteins, including several virulence factors, into its host:
;Streptolysin O and S
:These are [[Exotoxin|toxins]] which are the basis of the organism's beta-hemolytic property. Streptolysin O is a potent cell poison affecting many types of cell including neutrophils, platelets, and sub-cellular organelles. It causes an immune response and detection of antibodies to it; antistreptolysin O (ASO) can be clinically used to confirm a recent infection. Streptolysin O is cardiotoxic.
;Streptococcal pyogenic [[exotoxins]] (Spe) A and C
:SpeA and SpeC are [[superantigens]] secreted by many strains of ''S. pyogenes''. These pyogenic exotoxins are responsible for the [[rash]] of [[scarlet fever]] and many of the symptoms of streptococcal [[toxic shock syndrome]].
;[[Streptokinase]]
:Enzymatically activates [[plasminogen]], a proteolytic enzyme, into [[plasmin]] which in turn digests [[fibrin]] and other proteins.
;[[Hyaluronidase]]
:It is widely assumed that [[hyaluronidase]] facilitates the spread of the bacteria through tissues by breaking down [[hyaluronic acid]], an important component of [[connective tissue]]. However, very few isolates of ''S. pyogenes'' are capable of secreting active hyaluronidase due to mutations in the gene that encode the enzyme. Moreover, the few isolates that are capable of secreting hyaluronidase do not appear to need it to spread through tissues or to cause skin lesions.<ref name=Starr_2006>{{cite journal |author=Starr C, Engleberg N |title=Role of hyaluronidase in subcutaneous spread and growth of group A streptococcus |journal=Infect Immun |volume=74 |issue=1 |pages=40–8 |year=2006 |pmid=16368955 |doi=10.1128/IAI.74.1.40-48.2006}}</ref> Thus, the true role of hyaluronidase in pathogenesis, if any, remains unknown.
;Streptodornase
:Most strains of ''S. pyogenes'' secrete up to four different [[DNase]]s, which are sometimes called ''streptodornase''. The DNases protect the bacteria from being trapped in [[neutrophil extracellular traps]] (NETs) by digesting the NET's web of DNA, to which are bound [[neutrophil]] [[serine protease]]s that can kill the bacteria.<ref name=Buchanan_2006>{{cite journal |author=Buchanan J, Simpson A, Aziz R, Liu G, Kristian S, Kotb M, Feramisco J, Nizet V |title=DNase expression allows the pathogen group A Streptococcus to escape killing in neutrophil extracellular traps |journal=Curr Biol |volume=16 |issue=4 |pages=396–400 |year=2006 |pmid=16488874 |doi=10.1016/j.cub.2005.12.039}}</ref>
;[[C5a]] [[peptidase]]
:C5a peptidase cleaves a potent [[neutrophil]] chemotaxin called [[C5a]], which is produced by the complement system.<ref name=Wexler_1985>{{cite journal |author=Wexler D, Chenoweth D, Cleary P |title=Mechanism of action of the group A streptococcal C5a inactivator |journal=Proc Natl Acad Sci U S A |volume=82 |issue=23 |pages=8144–8 |year=1985 |pmid=3906656 |doi=10.1073/pnas.82.23.8144}}</ref> C5a peptidase is necessary to minimize the influx of neutrophils early in infection as the bacteria are attempting to colonize the host's tissue.<ref name="Ji 1996">{{cite journal |author=Ji Y, McLandsborough L, Kondagunta A, Cleary P |title=C5a peptidase alters clearance and trafficking of group A streptococci by infected mice |journal=Infect Immun |volume=64 |issue=2 |pages=503–10 |year=1996 |pmid=8550199}}</ref>
;Streptococcal chemokine protease
:The affected tissue of patients with severe cases of [[necrotizing fasciitis]] are devoid of [[neutrophil]]s.<ref name=Hidalgo-Grass_2004>{{cite journal |author=Hidalgo-Grass C, Dan-Goor M, Maly A, Eran Y, Kwinn L, Nizet V, Ravins M, Jaffe J, Peyser A, Moses A, Hanski E |title=Effect of a bacterial pheromone peptide on host chemokine degradation in group A streptococcal necrotising soft-tissue infections |journal=Lancet |volume=363 |issue=9410 |pages=696–703 |year=2004 |pmid=15001327 |doi=10.1016/S0140-6736(04)15643-2}}</ref> The [[serine protease]] ScpC, which is released by ''S. pyogenes'', is responsible for preventing the migration of neutrophils to the spreading infection.<ref name="Hidalgo-Grass 2006">{{cite journal |author=Hidalgo-Grass C, Mishalian I, Dan-Goor M, Belotserkovsky I, Eran Y, Nizet V, Peled A, Hanski E |title=A streptococcal protease that degrades CXC chemokines and impairs bacterial clearance from infected tissues |journal=EMBO J |volume=25 |issue=19 |pages=4628–37 |year=2006 |pmid=16977314 |doi=10.1038/sj.emboj.7601327}}</ref> ScpC degrades the [[chemokine]] [[Interleukin 8|IL-8]], which would otherwise attract [[neutrophil]]s to the site of infection. C5a peptidase, although required to degrade the neutrophil chemotaxin C5a in the early stages of infection, is not required for ''S. pyogenes'' to prevent the influx of neutrophils as the bacteria spread through the [[fascia]].<ref name="Ji 1996"/><ref name="Hidalgo-Grass 2006"/>
==Diagnosis==
Usually, a throat swab is taken to the laboratory for testing. A [[Gram stain]] is performed to show Gram positive, cocci, in chains. Then, culture the organism on [[blood agar]] with added [[bacitracin]] antibiotic disk to show [[Hemolysis (microbiology)|beta-haemolytic]] colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Then, perform [[catalase]] test, which should show a negative reaction for all ''Streptococci''. ''S. pyogenes'' is cAMP and [[hippurate]] tests negative. Serological identification of the organism involves testing for the presence of group A specific polysaccharide in the bacterium's cell wall using the [[Phadebact]] test.
==Treatment==
The treatment of choice is [[penicillin]], however in the absence of readily available penicillin, small incisions made to the infected area will relieve swelling and discomfort until proper medical assistance can be sought. There is no reported instance of penicillin-resistance reported to date, although since 1985 there have been many reports of penicillin-tolerance.<ref>{{cite journal|journal=J Pediatr|year=1985|volume=107|issue=5|pages=681–4|title=Association of penicillin tolerance with failure to eradicate group A streptococci from patients with pharyngitis|author=Kim KS, Kaplan EL|pmid=3903089|doi=10.1016/S0022-3476(85)80392-9}}</ref>
[[Macrolides]], [[chloramphenicol]], and [[tetracycline]]s may be used if the strain isolated has been shown to be sensitive, but resistance is much more common.
==References==
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===Other reading===
* Gladwin, Mark and Bill Trattler. ''Clinical Microbiology Made Ridiculously Simple, 3rd edition'', 2004.
* Brooks, Geo F., Janet S. Butel, and Stephen A. Morse. ''Jawetz, Melnick, and Adelberg's Medical Microbiology, 22nd edition'', 2001.
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