pyogenes (group A beta streptococci)
- Facultative anaerobe (def).
- Asymptomatic colonization of the
upper respiratory tract in humans.
- Pharyngitis is pread person to
person primarily by respiratory droplets; skin infections are spread by direct
contact with an infected person or through fomites (def).
- The most common infection is pharyngitis
(streptococcal sore throat) with the organism usually being limited to
the mucous membranes and lymphatic tissue of the upper respiratory tract.
From the pharynx, however,
the streptococci sometimes spread to other areas of the respiratory
tract resulting in laryngitis (def),
pneumonia, and otitis media (def).
- Occasionally, it may enter the
lymphatic vessels or the blood and disseminate to other areas of the
body, causing septicemia (def),
septic arthritis (def),
and meningitis (def).
- If it enters injured skin, it
may cause pyogenic (def)
cutaneous infections such as impetigo , erysipelas (def),
- Group A beta streptococcus infections
can result in two autoimmune diseases (def),
rheumatic fever and acute glomerulonephritis, where antibodies made against
streptococcal antigens cross react with joint membranes and heart valve tissue
in the case of rheumatic fever, or glomerular cells and basement membranes
of the kidneys in the case of acute glomerulonephritis.
strains of S. pyogenes cause invasive group A beta streptococcal
infections. Each year in the U.S. there are between 750 and 1500 cases of
where a streptococcal-coded protease called Exotoxin B destroys the muscle
(myositis) or the muscle covering (necrotizing fasciitis). There are another
750 - 1500 cases of toxic shock-like syndrome (def)
due to group A beta streptococci producing Streptococcal pyrogenic exotoxin
- A capsule of hyaluronic acid enables
the bacterium to resist phagocytic engulfment.
- Peptidoglycan fragments and teichoic
acids from its gram-positive cell wall can lead to excessive cytokine production
and a massive inflammatory response. Inflammation
in lung tissue results in the alveoli (def)
becoming filled with plasma (def)
which, in turn, prevents gas exchange.
- Lipoteichoic acid binds
to fibronectin on epithelial cells.
- M protein functions as an adhesin
and is antiphagocytic by leading to the degradation of the complement protein
C3b, a protein that promotes attachment of microbes to phagocytes.
- M-like proteins bind the antibodies
IgM and IgG.
- F protein is an adhesin (def)
that binds to fibronectin on epithelial cells.
- M protein and F protein rnable
S. pyogenes to invade epithelial cells and this helps maintain persistent
infections and spread to deeper tissues.
- Streptococcal pyrogenic exotoxin
(Spe), is a superantigen (def)
produced by rare invasive strains and scarlet fever strains of Streptococcus
pyogenes causes toxic shock-like syndrome (TSLS). Excessive cytokine
production leads to fever, rash, and shock.
- Streptolysin S and Streptolysin
O can lyse white blood cells, platelets, and red blood cells.
- Streptokinase can lyse fibrin
clots and facilitate the spread of bacteria through tissue.
- C5a peptidase degrades the complement
protein C5a that promotes inflammation and the chemotaxis of phagocytes to
the infected site.
- DNase degrades cell-free DNA in
purulent abcesses to reduce viscosity of the pus and facilitate spread of
*Drugs may change with time.
For a more detailed article on Streptococcus
pyogenes, see Streptococcus
Group A Infections, by Sat Sharma, MD, FRCPC, FACP, FCCP, DABSM, Program
Director, Associate Professor, Department of Internal Medicine, Divisions of
Pulmonary and Critical Care Medicine, University of Manitoba; Site Coordinator
of Respiratory Medicine, St Boniface General Hospital; and Godfrey
Harding, MD, FRCPC, Program Director of Medical Microbiology, Professor, Department
of Medicine, Section of Infectious Diseases and Microbiology, St Boniface Hospital,
University of Manitoba, Canada.
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Updated: Feb. 22, 2005
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