Virulence factor

A virulence factor is a property of a microorganism that determines its pathogenic effect . It can be both a structural element and a metabolic product of a microorganism. Genetically, virulence factors are often grouped into islands of pathogenicity . Meanwhile synonymous with virulence factor is also called virulence factor , although the pathogenicity describes the principle sickening quality, however, the virulence of the quantitative extent in triggering the disease.

Adhesins

Adhesins are fimbriae or membrane proteins that enable bacteria to adhere to target cells. The adhesins react with the host cell's homologous receptors .

Antiphagocytic factors

Antiphagocytic factors prevent phagocytosis . This means that the bacterium is not absorbed and destroyed by the immune system 's phagocytes . Various components of bacteria can have anti-phagocytic effects:

Capsule : The bacterial capsule consists of sugar or amino acid compounds. Encapsulated, pathogenic bacteria are, for example, pneumococci .

M-protein of the A-streptococci : Streptococci of the Lancefield group A have a surface protein which, however , can be inactivated by antibodies .

Protein A from Staphylococcus aureus : Protein A binds the IgG of the defense "upside down", namely at the Fc end , which means that it cannot work ( anti-osmotic effect)

Leukozidines : Leukozidines are bacterial metabolic products that have a damaging effect on phagocytes ("scavenger cells"). For example, Staphylococcus aureus has leukozidines.

Coagulase : This protein is secreted by, for example, Staphylococcus aureus . Coagulase and prothrombin together form coagulothrombin, which converts the bound fibrinogen into fibrin . Fibrin forms a slimy protective layer for the bacteria.

Clumping Factor A from Staphylococcus aureus is a surface protein which binds fibrinogen.

Invasion Factors

Invasion factors allow the pathogens to spread in the tissue. These include, for example:

Streptokinase : e.g. B. in A streptococci such as Streptococcus pyogenes . Streptokinase activates plasmin , which leads to fibrinolysis , i.e. the dissolution of fibrin.
Hyaluronidase : Hyaluronidase attacks the hyaluronic acid of the connective tissue and is also known as the "spreading factor". This virulence factor is developed, for example, in A streptococci, pneumococci, staphylococci and Clostridium perfringens .
Scourge : Scourges enable the active mobility of the bacteria
Protease : dissolution of proteins (egg white)
DNase : dissolution of DNA
Lipase : dissolution of lipids (fats)

Endotoxins

Endotoxins are microbial toxins (poisonous substances) from the outer membrane of Gram-negative bacteria. The only known endotoxin is lipid A , which is found in all gram-negative bacteria in the lipopolysaccharides (LPS) of the outer membrane. Lipid A is released when the bacterium dies and then unfolds its toxic effect:

Interleukin-1 is released from macrophages , causing a febrile reaction
TNFα ( tumor necrosis factor α ) is released. This leads to an enlargement of the arteries ( vasodilation ), thus making it an septic shock may occur
Lipid A binds receptors on B-cell, thus causing a maturation of the B-lymphocytes is
The complement system is activated via the alternative route
Affecting the kinin system and blood clotting

In the course of sepsis (blood poisoning) with gram-negative pathogens, endotoxin poisoning can occur after antibiotic therapy, as a large amount of endotoxin is released due to the massive death of the pathogens. This can lead to shock .

Exotoxins

Exotoxins are toxins secreted by living bacteria. Often they are only produced by bacteria that are infected by a bacteriophage . Different modes of action of the exotoxins are: