Enzymes & Toxins of Staphylococcus

Enzymes & Toxins of Staphylococcus
Staphylococci can produce disease both through their ability to multiply and spread widely in tissues and through their production of many extracellular substances. Some of these substances are enzymes; others are considered to be toxins, though they may function as enzymes. Many of the toxins are under the genetic control of plasmids; some may be under both chromosomal and extrachromosomal control;

1-Catalase
Staphylococci produce catalase, which converts hydrogen peroxide into water and oxygen.
2-Coagulase and Clumping Factor
S aureus produces coagulase, an enzyme-like protein that clots oxalated or citrated plasma. Coagulase binds to prothrombin; together they become enzymatically active and initiate fibrin polymerization. Coagulase may deposit fibrin on the surface of staphylococci, perhaps altering their ingestion by phagocytic cells or their destruction within such cells.
3-Clumping factor is a surface S aureus compound that is responsible for adherence of the organisms to fibrinogen and fibrin. When mixed with plasma, S aureus forms clumps. Clumping factor is distinct from coagulase.
4-Other Enzymes
Other enzymes produced by staphylococci include a hyaluronidase, or spreading factor; a staphylokinase resulting in fibrinolysis but acting much more slowly than streptokinase; proteinases; lipases; and B-lactamase.
Exotoxins
The toxin is a heterogeneous protein that acts on a broad spectrum of eukaryotic cell membranes. The toxin is a potent hemolysin. & degrades sphingomyelin and therefore is toxic for many kinds of cells, including human red blood cells. The toxin is heterogeneous and dissociates into subunits in nonionic detergents. It disrupts biologic membranes and may have a role in S aureus diarrheal diseases.
1-The hemolysin refers to three proteins that interact with the two proteins comprising the Panton-Valentine leukocidin to form six potential two-component toxins. All six of these protein toxins are capable of efficiently lysing white blood cells by causing pore formation in the cellular membranes that increase cation permeability.
2-Leukocidin
This toxin of S aureus has two components. It can kill white blood cells of humans and rabbits.
3-Exfoliative Toxins
These epidermolytic toxins of S aureus are two distinct proteins of the same molecular weight. Epidermolytic toxin A is a chromosomal gene product and is heat-stable (resists boiling for 20 minutes). Epidermolytic toxin B is plasmid-mediated and heat-labile. The epidermolytic toxins yield the generalized desquamation of the staphylococcal scalded skin syndrome by dissolving the mucopolysaccharide matrix of the epidermis. The toxins are superantigens.
4-Toxic Shock Syndrome Toxin
Most S aureus strains isolated from patients with toxic shock syndrome produce a toxin called toxic shock syndrome toxin-1 (TSST-1), which is the same as enterotoxin F. TSST-1 is the prototypical superantigen & it is associated with fever, shock, and multisystem involvement, including a desquamative skin rash. The gene for TSST-1 is found in about 20% of S aureus isolates.
5-Enterotoxins
There are multiple (A–E, G–I, K–M) enterotoxins. Approximately 50% of S aureus strains can produce one or more of them. Like TSST-1, the enterotoxins are superantigens. The enterotoxins are heat-stable and resistant to the action of gut enzymes. An important cause of food poisoning, enterotoxins are produced when S aureus grows in carbohydrate and protein foods. Ingestion of 25 mg of enterotoxin B results in vomiting and diarrhea. The emetic effect of enterotoxin is probably the result of central nervous system stimulation (vomiting center) after the toxin acts on neural receptors in the gut.
The exfoliative toxins, TSST-1, and the enterotoxin genes are on a chromosomal element called a pathogenicity island. It interacts with accessory genetic elements—bacteriophages—to produce the toxins.