Streptococcus pyogenes
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| Image:Streptococcus pyogenes 01.jpg S. pyogenes bacteria @ 900x magnification.
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| Streptococcus pyogenes Rosenbach 1884 |
Streptococcus pyogenes is a Gram-positive cocci that grows in long chains depending on the culture method.<ref name=Sherris>Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.</ref> S. pyogenes displays group A antigen on its cell wall and beta-hemolysis when cultured on blood agar plate. S. pyogenes typically produces large zones of beta-hemolysis, the complete disruption of erythrocytes and the release of hemoglobin, and it is therefore called Group A (beta-hemolytic) Streptococcus (abbreviated GAS).
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[edit] 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> Lancefield RC (1928). "The antigenic complex of Streptococcus hemolyticus. I. Demonstration of a type-specific substance in extracts of Streptococcus hemolyticus." J Exp Med 47:9-10</ref>. Later in 1946, Lancefield described the serologic classification of S. pyogenes isolates based on their surface T antigen.<ref>Lancefield RC and Dole VP (1946). "The properties of T antigen extracted from group A hemolytic streptococci." J Exp Med 84:449-471.</ref> Four of the 20 T antigens have been revealed to be pili, which are used by bacteria to attach to host cells.<ref>Mora M, Bensi G, Capo S, Fabiana F, Zingaretti C, Manetti AGO, Maggi T, Taddei AR, Grandi G, and Telford JL (2005). "Group A Streptococcus produce pilus-like structuers containing protective antigens and Lancefield T antigens." PNAS 102(43):15641-15646.</ref> Currently, over 100 M serotypes and approximately 20 T serotypes are known.
[edit] Virulence factors
S. pyogenes has several virulence factors.<ref name=Baron>Patterson MJ (1996). Streptococcus. In: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.</ref> A carbohydrate capsule surrounds the bacterium, protecting it from attack by macrophages (part of the immune system). Further, there are proteins, lipoteichoic acids, embedded within the capsule (M protein) that also increase virulence by facilitating attachment to host cells.<ref name=Bisno_2003>Bisno AL, Brito MO, Collins CM (2003). "Molecular basis of group A streptococcal virulence". Lancet Infect Dis 3 (4): 191-200. PubMed.</ref> M protein inhibits a branch of the immune system called the complement system, which binds to and destroys invading bacteria. However, the M protein is also the weakest point in this organism's defense as this is what antibodies produced by the immune system use to recognize the bacterium. M proteins are unique to each strain and identification can be used clinically to confirm the strain causing an infection.
There are several virulence factors that S. pyogenes releases into its host:
- Streptolysin O and S
- 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.
- Pyogenic toxin
- Found in strains of S. pyogenes responsible for scarlet fever.
- Streptokinase
- Enzymatically activates plasminogen, a proteolytic enzyme, into plasmin which in turn digests fibrin and other proteins.
- Hyaluronidase
- Breaks down hyaluronic acid, an important component of connective tissue, facillitating the spread of the infection.
- Streptodornase
- A DNAase which depolymerizes DNA
- Other toxins
- Including anti-C5a peptidase, and others.
[edit] Pathogenesis
S. pyogenes is associated with many important diseases. Diseases it can cause through its release of toxins are: streptococcal pharyngitis, streptococcal skin infections (cellulitis, erysipelas, possibly even necrotizing fasciitis), scarlet fever, and streptococcal toxic shock syndrome. It can also cause disease through the reaction of the immune system to it. These diseases are rheumatic fever and glomerulonephritis.
This bacterium is very sensitive to penicillin.
[edit] References
<references />
- McDaniel, Larry. "Gram Positive Pyogenic Cocci", lecture to 2nd year medical students (September 20, 2005, University of Mississippi Medical Center.
- 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.de:Streptococcus pyogenes
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