Streptococcus pyogenes

Streptococcus pyogenes
S. pyogenes bacteria at 900x magnification
Scientific classification
Kingdom: Eubacteria
Phylum: Firmicutes
Class: Cocci
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species: S. pyogenes
Binomial name
Streptococcus pyogenes
Rosenbach 1884

Streptococcus pyogenes is a species of bacteria. Like most other streptococci, it is clinically important in human illness. It is an infrequent, but usually pathogenic, part of the skin flora. It is the sole species of Lancefield group A and is often called group A streptococcus (GAS), because it displays streptococcal group A antigen on its cell wall. Group A streptococcal infection can cause illness, which typically produces small zones of beta-hemolysis, a complete destruction of red blood cells. (A zone size of 2-3 mm is typical). It is thus also called group A (beta-hemolytic) streptococcus (GABHS).

Like other cocci, streptococci are round bacteria. The name derives from the Greek word streptos, meaning twisted chain, because streptococcal cells tend to link together in chains, which resemble a string of pearls when viewed under the microscope.[1] Streptococci are catalase-negative and Gram-positive.[2] S. pyogenes can be cultured on blood agar plates. Under ideal conditions, it has an incubation period of 1 to 3 days.[3]

An estimated 700 million GAS infections occur worldwide each year. While the overall mortality rate for these infections is 0.1%, over 650,000 of the cases are severe and invasive, and have a mortality rate of 25%.[4] Early recognition and treatment are critical; diagnostic failure can result in sepsis and death.[5][6]

Serotyping

In 1928, Rebecca Lancefield published a method for serotyping S. pyogenes based on its M protein, a virulence factor displayed on its surface.[7] Later, in 1946, Lancefield described the serologic classification of S. pyogenes isolates based on their surface T antigen.[8] Four of the 20 T antigens have been revealed to be pili, which are used by bacteria to attach to host cells.[9] Over 220 M serotypes and about 20 T serotypes are known. This is why the plural term group A streptococci (referring to the serotypes) and the singular term group A streptococcus (referring to the single species) are both commonly encountered.

Pathogenesis

S. pyogenes is the cause of many important human diseases, ranging from mild superficial skin infections to life-threatening systemic diseases.[2] Infections typically begin in the throat or skin. The most striking sign is a strawberry-like rash. 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 life-threatening condition requiring surgery.

Infections due to certain strains of S. pyogenes can be associated with the release of bacterial 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.[2]

S. pyogenes can also cause disease in the form of postinfectious "nonpyogenic" (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 postinfectious 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 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.[10] A carbohydrate-based bacterial capsule composed of hyaluronic acid surrounds the bacterium, protecting it from phagocytosis by neutrophils.[2] 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.[11] M protein also inhibits opsonization by the alternative complement pathway by binding to host complement regulators. The M protein found on some serotypes is also able to prevent opsonization by binding to fibrinogen.[2] However, the M protein is also the weakest point in this pathogen's defense, as 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.

Name Description
Streptolysin O An exotoxin, one of the bases of the organism's beta-hemolytic property, streptolysin O causes an immune response and detection of antibodies to it; antistreptolysin O (ASO) can be clinically used to confirm a recent infection.
Streptolysin S A cardiotoxic exotoxin, another beta-hemolytic component, not immunogenic and O2 stable: A potent cell poison affecting many types of cell including neutrophils, platelets, and subcellular organelles.
Streptococcal pyrogenic exotoxin A (SpeA) Superantigens secreted by many strains of S. pyogenes: This pyrogenic exotoxin is responsible for the rash of scarlet fever and many of the symptoms of streptococcal toxic shock syndrome, also known as toxic shock like syndrome(TSLS).
Streptococcal pyrogenic exotoxin C (SpeC)
Streptokinase Enzymatically activates plasminogen, a proteolytic enzyme, into plasmin, which in turn digests fibrin and other proteins
Hyaluronidase Hyaluronidase is widely assumed to facilitate 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 capable of secreting hyaluronidase do not appear to need it to spread through tissues or to cause skin lesions.[12] Thus, the true role of hyaluronidase in pathogenesis, if any, remains unknown.
Streptodornase Most strains of S. pyogenes secrete up to four different DNases, which are sometimes called streptodornase. The DNases protect the bacteria from being trapped in neutrophil extracellular traps (NETs) by digesting the NETs' web of DNA, to which are bound neutrophil serine proteases that can kill the bacteria.[13]
C5a peptidase C5a peptidase cleaves a potent neutrophil chemotaxin called C5a, which is produced by the complement system.[14] C5a peptidase is necessary to minimize the influx of neutrophils early in infection as the bacteria are attempting to colonize the host's tissue. [15] 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. [16]
Streptococcal chemokine protease The affected tissue of patients with severe cases of necrotizing fasciitis are devoid of neutrophils.[17] The serine protease ScpC, which is released by S. pyogenes, is responsible for preventing the migration of neutrophils to the spreading infection. ScpC degrades the chemokine IL-8, which would otherwise attract neutrophils to the site of infection. [15][16]

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, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta-hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on agar not containing blood, and then performing the catalase test 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.[18][19] Pyrrolidonyl Arylamidase (PYR) test is a rapid test which is used for the presumptive identification of group A beta-hemolytic Streptococci. GBS gives positive finding on this test. [20]

Treatment

The treatment of choice is penicillin, and the duration of treatment is well established as being 10 days minimum.[21] For toxic shock syndrome and necrotizing fasciitis, high-dose penicillin and clindamycin are used. Additionally, for necrotizing fasciitis, surgery is often needed to remove damaged tissue and stop the spread of the infection.[22]

No instance of penicillin resistance has been reported to date, although since 1985, many reports of penicillin tolerance have been made.[23] The reason for the failure of penicillin to treat S. pyogenes is most commonly patient noncompliance, but in cases where patients have been compliant with their antibiotic regimen, and treatment failure still occurs, another course of antibiotic treatment with cephalosporins is common.[24]

In individuals with a penicillin allergy, erythromycin, other macrolides, and cephalosporins have been shown to be effective treatments.[24]

Prevention

S. pyogenes infections are best prevented through effective hand hygiene.[22] No vaccines are currently available to protect against S. pyogenes infection, although research has been conducted into the development of one.[25] Difficulties in developing a vaccine include the wide variety of strains of S. pyogenes present in the environment and the large amount of time and number of people that will be needed for appropriate trials for safety and efficacy of the vaccine.[25][26]

Applying in bionanotechnology

Many S. pyogenes proteins have unique properties, which have been harnessed in recent years to produce a highly specific "superglue"[27][28] and a route to enhance the effectiveness of antibody therapy.[29]

Genome

The genome of different strains were sequenced (genome size is 1.8-1.9 Mbp)[30] encoding about 1700-1900 proteins (1700 in strain NZ131,[31][32] 1865 in strain MGAS5005 [33][34]).

See also

References

  1. ↑ "Definition of Streptococcus pneumoniae (pneumococcus)". Retrieved November 21, 2012.
  2. 1 2 3 4 5 Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
  3. ↑ Streptococcal Pharyngitis
  4. ↑ Aziz RK, Kansal R, Aronow BJ, Taylor WL, Rowe SL, Kubal M, Chhatwal GS, Walker MJ, Kotb M (2010). Ahmed, Niyaz, ed. "Microevolution of Group A Streptococci In Vivo: Capturing Regulatory Networks Engaged in Sociomicrobiology, Niche Adaptation, and Hypervirulence". PLoS ONE 5 (4): e9798. doi:10.1371/journal.pone.0009798. PMC 2854683. PMID 20418946. Retrieved 2011-08-12.
  5. ↑ Jim Dwyer (July 11, 2012). "An Infection, Unnoticed, Turns Unstoppable". The New York Times. Retrieved July 12, 2012.
  6. ↑ Jim Dwyer (July 18, 2012). "After Boy’s Death, Hospital Alters Discharging Procedures". The New York Times. Retrieved July 19, 2012.
  7. ↑ Lancefield RC (1928). "The antigenic complex of Streptococcus hemolyticus". J Exp Med 47 (1): 9–10. doi:10.1084/jem.47.1.91.
  8. ↑ Lancefield RC, Dole VP (1946). "The properties of T antigen extracted from group A hemolytic streptococci". J Exp Med 84 (5): 449–71. doi:10.1084/jem.84.5.449. PMC 2135665. PMID 19871581.
  9. ↑ Mora M, Bensi G, Capo S, Falugi F, Zingaretti C, Manetti AG, Maggi T, Taddei AR, Grandi G, Telford JL (2005). "Group A Streptococcus produce pilus-like structures containing protective antigens and Lancefield T antigens". Proc Natl Acad Sci USA 102 (43): 15641–6. doi:10.1073/pnas.0507808102. PMC 1253647. PMID 16223875.
  10. ↑ Patterson MJ (1996). Streptococcus. In: Baron's Medical Microbiology (Baron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.
  11. ↑ Bisno AL, Brito MO, Collins CM (2003). "Molecular basis of group A streptococcal virulence". Lancet Infect Dis 3 (4): 191–200. doi:10.1016/S1473-3099(03)00576-0. PMID 12679262.
  12. ↑ Starr CR, Engleberg NC (2006). "Role of Hyaluronidase in Subcutaneous Spread and Growth of Group A Streptococcus". Infect Immun 74 (1): 40–8. doi:10.1128/IAI.74.1.40-48.2006. PMC 1346594. PMID 16368955.
  13. ↑ Buchanan JT, Simpson AJ, Aziz RK, Liu GY, Kristian SA, Kotb M, Feramisco J, Nizet V (2006). "DNase expression allows the pathogen group A Streptococcus to escape killing in neutrophil extracellular traps". Curr Biol 16 (4): 396–400. doi:10.1016/j.cub.2005.12.039. PMID 16488874.
  14. ↑ Wexler DE, Chenoweth DE, Cleary PP (1985). "Mechanism of action of the group A streptococcal C5a inactivator". Proc Natl Acad Sci USA 82 (23): 8144–8. doi:10.1073/pnas.82.23.8144. PMC 391459. PMID 3906656.
  15. 1 2 Ji Y, McLandsborough L, Kondagunta A, Cleary PP (1996). "C5a peptidase alters clearance and trafficking of group A streptococci by infected mice". Infect Immun 64 (2): 503–10. PMC 173793. PMID 8550199.
  16. 1 2 Hidalgo-Grass C, Mishalian I, Dan-Goor M, Belotserkovsky I, Eran Y, Nizet V, Peled A, Hanski E (2006). "A streptococcal protease that degrades CXC chemokines and impairs bacterial clearance from infected tissues". EMBO J 25 (19): 4628–37. doi:10.1038/sj.emboj.7601327. PMC 1589981. PMID 16977314.
  17. ↑ Hidalgo-Grass C, Dan-Goor M, Maly A, Eran Y, Kwinn LA, Nizet V, Ravins M, Jaffe J, Peyser A, Moses AE, Hanski E (2004). "Effect of a bacterial pheromone peptide on host chemokine degradation in group A streptococcal necrotising soft-tissue infections". Lancet 363 (9410): 696–703. doi:10.1016/S0140-6736(04)15643-2. PMID 15001327.
  18. ↑ Kellogg JA, Bankert DA, Elder CJ, Gibbs JL, Smith MC (September 2001). "Identification of Streptococcus pneumoniae revisited". J. Clin. Microbiol. 39 (9): 3373–5. doi:10.1128/jcm.39.9.3373-3375.2001. PMC 88350. PMID 11526182.
  19. ↑ Burdash NM, West ME (March 1982). "Identification of Streptococcus pneumoniae by the Phadebact coagglutination test". J. Clin. Microbiol. 15 (3): 391–4. PMC 272105. PMID 7076811.
  20. ↑ http://microbeonline.com/pyrrolidonyl-arylamidase-pyr-test-principle-procedure-results
  21. ↑ Falagas ME, Vouloumanou EK, Matthaiou DK, Kapaskelis AM, Karageorgopoulos DE (2008). "Effectiveness and safety of short-course vs long-course antibiotic therapy for group a beta hemolytic streptococcal tonsillopharyngitis: a meta-analysis of randomized trials". Mayo Clin Proc 83 (8): 880–9. doi:10.4065/83.8.880. PMID 18674472.
  22. 1 2 "Group A Strep". CDC.gov. CDC. Retrieved 7 December 2014.
  23. ↑ Kim KS, Kaplan EL (1985). "Association of penicillin tolerance with failure to eradicate group A streptococci from patients with pharyngitis". J Pediatr 107 (5): 681–4. doi:10.1016/S0022-3476(85)80392-9. PMID 3903089.
  24. 1 2 Khan, Zartash. "Group A Streptococcal Infections Treatment & Management". Medscape. Retrieved 7 December 2014.
  25. 1 2 Good MF, Batzloff MR, Pandey M (November 2013). "Strategies in the development of vaccines to prevent infections with group A streptococcus". Human vaccine & immunotherapeutics 9 (11): 2393–7. doi:10.4161/hv.25506. PMC 3981849. PMID 23863455.
  26. ↑ "Initiative for Vaccine Research (IVR) – Group A Streptococcus". World Health Organization. Retrieved 15 June 2012.
  27. ↑ http://www.ox.ac.uk/news/science-blog/flesh-eating-bacteria-inspire-superglue
  28. ↑ Zakeri B, Fierer JO, Celik E, Chittock EC, Schwarz-Linek U, Moy VT, Howarth M (2012). "Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin". Proceedings of the National Academy of Sciences 109 (12): E690–7. doi:10.1073/pnas.1115485109. PMC 3311370. PMID 22366317.
  29. ↑ Baruah K, Bowden TA, Krishna BA, Dwek RA, Crispin M, Scanlan CN (2012). "Selective Deactivation of Serum IgG: A General Strategy for the Enhancement of Monoclonal Antibody Receptor Interactions". Journal of Molecular Biology 420 (1–2): 1–7. doi:10.1016/j.jmb.2012.04.002. PMC 3437440. PMID 22484364.
  30. ↑ Beres SB, Richter EW, Nagiec MJ, Sumby P, Porcella SF, DeLeo FR, Musser JM (2006). "Molecular genetic anatomy of inter- and intraserotype variation in the human bacterial pathogen group a Streptococcus". Proceedings of the National Academy of Sciences 103 (18): 7059–64. doi:10.1073/pnas.0510279103. PMC 1459018. PMID 16636287.
  31. ↑ Streptococcus pyogenes NZ131 in MicrobesOnline
  32. ↑ McShan, W. M.; Ferretti, J. J.; Karasawa, T; Suvorov, A. N.; Lin, S; Qin, B; Jia, H; Kenton, S; Najar, F; Wu, H; Scott, J; Roe, B. A.; Savic, D. J. (2008). "Genome sequence of a nephritogenic and highly transformable M49 strain of Streptococcus pyogenes". Journal of Bacteriology 190 (23): 7773–85. doi:10.1128/JB.00672-08. PMC 2583620. PMID 18820018.
  33. ↑ Sumby, P; Porcella, S. F.; Madrigal, A. G.; Barbian, K. D.; Virtaneva, K; Ricklefs, S. M.; Sturdevant, D. E.; Graham, M. R.; Vuopio-Varkila, J; Hoe, N. P.; Musser, J. M. (2005). "Evolutionary origin and emergence of a highly successful clone of serotype M1 group a Streptococcus involved multiple horizontal gene transfer events". The Journal of Infectious Diseases 192 (5): 771–82. doi:10.1086/432514. PMID 16088826.
  34. ↑ Streptococcus pyogenes MGAS5005 in MicrobesOnline

Further reading

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