Streptococcus pyogenes

Streptococcus pyogenes

Streptococcus pyogenes (from Greek πύον pus - pus -causing streptococci) is a common bacterium that can cause in humans, among other things scarlet and double-sided purulent tonsillitis.

Properties

Streptococcus pyogenes is Gram- positive, chain- forming, facultative anaerobic - and beta- hemolytic. The single, round cell has a size of 0.6 to 1 micron. S. pyogenes can not actively move and does not form spores. On blood agar, a nutrient medium containing blood, arising grauweißlich slimy colonies. After Lancefield diagram Streptococcusarten differentiated according to their C- polysaccharide, S. pyogenes is one of the group A.

Pathogenesis and disease caused

Streptococcus pyogenes has several virulence factors that allow the bacteria to evade the immune response of the human immune system and cause disease. One of the major virulence factors of the M protein, a surface protein antiphagozytotisches. Has a similar effect existing in some strains of hyaluronic acid capsule. In addition, a C5a peptidase cleaves important signaling molecules in the complement system and thus prevents the activation of this part of the immune system.

The fibronectin -binding proteins F1 and SfbI the bacterium for adhering to the endothelial cells and thus support its penetration into human tissue. Once there, the Streptolysine O and S destroy red blood cells and other cells. The streptokinase dissolves fibrin. In addition, several enzymes such as DNases, proteases and hyaluronidases help the bacterium during propagation in tissue. To be able to hold its own against other bacteria, S. pyogenes secretes further bacterial toxins.

Streptococcus pyogenes causing invasive infections, both acute and non - invasive sequelae. The acute infections go here because of the many tissue-dissolving enzymes often associated with pus formation. One possible target is the upper respiratory tract, where an almond or throat inflammation can be formed. On the skin may occur, depending on the depth of the infection and the immune status impetigo, erysipelas or cellulitis. Local infection may be a poor defensive position in a generalized infection pass (sepsis).

When the Streptococcus bacterium by a β virus prophage has been infected, it can form using the virus genome, a Streptococcus pyogenes exotoxin (PSE). This PSE exists in three variants A, B and C, where A and C act as superantigens. PSE B cleaves immunoglobulins. All three toxins can also cause scarlet fever. When equipped the immune system with high-risk MHCII allotypes may lead to necrotizing fasciitis or a streptococcal -induced toxic shock syndrome ( STSS ).

Especially feared are the immunological sequelae of streptococcal infection, particularly acute glomerulonephritis and acute rheumatic fever. There is acute glomerulonephritis, which occurs about three weeks after the actual infection, to distinguish from the occurring with the infection acute interstitial nephritis. This takes place an excessive cell- mediated immune response as a nonbacterial inflammation of the renal interstitium in the frame. In Glomerulonephritis occurs by deposition of antigen -antibody complexes ( immune complex disease, type III), damage to the kidney. In acute rheumatic fever play cross-reactions between antigens of streptococcal and body's structures, particularly collagen IV, a role. This leads to inflammation in the heart ( endocarditis, myocarditis, pericarditis ), in joints (arthritis), brain ( chorea ) and in the skin (erythema ), or in rare cases in the muscle ( pyomyositis ). In the subcutaneous nodules form.

Diagnostics

Depending on the location of the disease blood, aspirates, biopsy material or pus swabs may be examined in the laboratory. Where the typical chains can already be recognized under the microscope. To grow S. pyogenes, we used agar plates of meat extract, blood or serum is added. At 37 ° C and 5 to 10 % carbon dioxide in 16 to 24 is expected to colony formation hours.

For the differentiation of the C- polysaccharide (see above) can be used in commercial ELISA that work with antibodies. The genes for the M protein ( emm genes) are sometimes studied for scientific purposes.

If there is a suspicion of a problem caused by S. pyogenes rheumatic fever before, the patient may for antibodies to streptolysin O ( see above) and are examined against the DNAse.

Therapy

Streptococci can be well controlled with penicillins. In intolerance macrolide antibiotics are used.

Epidemiology

S. pyogenes occurs worldwide. It only infects humans, but here is one of the most common pathogens of skin and respiratory diseases. It is noticeable that in temperate climates the throat infections play the largest role, while more skin infections occur in tropical countries. The transfer of germs occurs both by droplet and by smear infection. Although in humans, in which no disease has occurred, germs can be demonstrated apparent ill are more common source of infection.

Others

Two enzymes of S. pyogenes are used in medicine for therapeutic purposes The streptokinase is used to dissolve blood clots which DNAses are used in the treatment of wounds.

In the "battle " with macrophages S. pyogenes attacks using Cytolysinen not only their cell membrane, but in a cascaded process the mitochondria.