Streptococcus pyogenes
From Free net encyclopedia
{{Taxobox | color = lightgrey | name = Streptococcus pyogenes | image = Streptococcus_pyogenes_01.jpg | image_width = 240px | image_caption = S. pyogenes bacteria @ 900x magnification. | regnum = 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 gram-positive bacterium that will grow in pairs or chains depending on the culture method used. The gram stain is a method microbiologists use to divide bacteria into two structurally and functionally different categories, based on their anatomy. S. pyogenes displays group A antigen on its cell wall and beta-hemolysis when cultured on blood agar plate. It typically produces large zones of beta-hemolysis, the complete disruption of erythrocytes and the release of hemoglobin. It is therefore called Group A Beta-hemolytic streptococcus.
Virulence factors
S. pyogenes has several attributes that make it more virulent (these are called "virulence factors"). A carbohydrate capsule surrounds the bacterium, protecting it from being destroyed by macrophages (an arm of the immune system). There are proteins, lipoteichoic acids, embedded within the capsule (M protein) that also make it more virulent by facilitating attachment to host cells. 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. The type of M protein used is unique to each strain and its identification can be used clinically to identify the specific strain causing 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 can cause an immune response and detection of antibodies to it, antistreptolysin O (ASO) can be clinically used to confirm a recent infection.
- Pyogenic toxin
- Found only in certain strains of S. pyogenes, but these are the strains responsible for scarlet fever.
- Streptokinase
- Enzymatically activates Plasminogen, a proteolytic enzyme, into plaosmin which in turn digests fibrin and other proteins.
- Hyaluronidase
- Breaks down hyaluronic acid which is an important component of connective tissue. This in turn facilitates the spread of the infection
- Streptodornase
- DNAase which deploymerizes DNA
- Other toxins
- Including anti-C5a peptidase, and others.
Diseases
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.
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
lt:Streptococcus pyogenes nl:Streptococcus pyogenes pt:Streptococcus pyogenes