Sandbox: GAS pathophysiology

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Transmission

Group A streptococcal infection can be transmitted by the following:[1]

  • Direct inter-personal transmission
  • Infected airborne droplets

Virulence factors

Group A streptococcus are responsible for various diseases ranging from mild to life threatening cases. The bacteria depends mainly on many virulence factors which are responsible for the pathogenesis of the infections.[1]

Virulence factors Mechanism of action
M - protein
  • The most important virulence factor.
  • It prevents the phagocytosis of the bacteria by binding to the fibrinogen and prevents binding the complement to the bacterial cell wall.
Streptolysin O and S
  • Streptolysin O works on killing the differecnt cells like the neutrophils, platelets and the sub-cellular organelles.
Streptococcal pyrogenic exotoxins A and C
  • SpeA and SpeC are superantigens secreted by many strains of S. pyogenes. These pyrogenic exotoxins are responsible for the rash of scarlet fever and many of the symptoms of streptococcal toxic shock syndrome.
Streptokinase
  • Enzymatically activates plasminogen which is a proteolytic enzyme into plasmin which in turn digests fibrin and other proteins.
Hyalourinidase
  • It helps the bacteria to spread through the tissue by destroying the hyaluronic acid which is a connective tissue component.[2]
Streptodornase
C5a peptidase
  • C5a peptidase cleaves a potent neutrophil chemotaxin called C5a, which is produced by the complement system.[4] C5a peptidase is necessary to minimize the influx of neutrophils early in infection as the bacteria are attempting to colonize the host's tissue.[5].
Streptococcal chemokine protease
  • The affected tissue of patients with severe cases of necrotizing fasciitis are devoid of neutrophils.[6]. The serine protease ScpC, which is released by S. pyogenes, is responsible for preventing the migration of neutrophils to the spreading infection.[7] ScpC degrades the chemokine IL-8, which would otherwise attract neutrophils 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.[5][7]

Pathogenesis

  • The initial step in pathogenesis of group a streptococcus, in order to cause infection, is the adhesion and colonization of the bacteria to the epithelial cells.[8][9].The bacteria adheses and invades the cell leading to tissue destruction and infection.

References

  1. ↑ 1.0 1.1 Brouwer S, Barnett TC, Rivera-Hernandez T, Rohde M, Walker MJ (2016). "Streptococcus pyogenes adhesion and colonization". FEBS Lett. 590 (21): 3739–3757. doi:10.1002/1873-3468.12254. PMID 27312939.
  2. ↑ Starr C, Engleberg N (2006). "Role of hyaluronidase in subcutaneous spread and growth of group A streptococcus". Infect Immun. 74 (1): 40–8. PMID 16368955.
  3. ↑ Buchanan J, Simpson A, Aziz R, Liu G, Kristian S, 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. PMID 16488874.
  4. ↑ Wexler D, Chenoweth D, Cleary P (1985). "Mechanism of action of the group A streptococcal C5a inactivator". Proc Natl Acad Sci U S A. 82 (23): 8144–8. PMID 3906656.
  5. ↑ 5.0 5.1 Ji Y, McLandsborough L, Kondagunta A, Cleary P (1996). "C5a peptidase alters clearance and trafficking of group A streptococci by infected mice". Infect Immun. 64 (2): 503–10. PMID 8550199.
  6. ↑ Hidalgo-Grass C, Dan-Goor M, Maly A, Eran Y, Kwinn L, Nizet V, Ravins M, Jaffe J, Peyser A, Moses A, 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. PMID 15001327.
  7. ↑ 7.0 7.1 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. PMID 16977314.
  8. ↑ Courtney HS, Hasty DL, Dale JB (2002). "Molecular mechanisms of adhesion, colonization, and invasion of group A streptococci". Ann Med. 34 (2): 77–87. PMID 12108578.
  9. ↑ Moschioni M, Pansegrau W, Barocchi MA (2010). "Adhesion determinants of the Streptococcus species". Microb Biotechnol. 3 (4): 370–88. doi:10.1111/j.1751-7915.2009.00138.x. PMC 3815805. PMID 21255337.
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