exotoxins

exotoxins

1. Cytolytic toxins: degrade cytoplasmic membrane integrity cause cell lysis & death

   • hemolysins: toxin lyse RBC
     • phospholipases: attach phospholipids of host cytoplasmic membrane
       • lecithinase ( alpha toxin) produced by Clostridium perfringens produce dissolve membrane lipids in plants and animals. can cause myonecrosis and hemolysis
     • nonphospholipases
       • Streptolysin O: (streptocci pyogenes) affect sterols of host cytoplasmic membrane
       • Leukocidins: lyse white blood cells and may decrease immune response
       • Staphylococcal alpha toxin kills nucleated cells and lyses RBCs

2. AB toxins: consist of 2 subunits A and B. A subunit is the damaging agent trasnferred across cell membrane and B subunit is used to bind to host cell receptor

   • diphtheria toxin: produced by Corynebacterium diphtheriae. inhibits protein synthesis in eukaryotes. rats and mice resistant.
   • Clostridium botulinum: endospore forming bacteria commonly found in soil. neurotoxin, not very invasive. prevent release of acetylcholine from vesicicles which inhibits contraction
   • Clostridium tetani: endospore forming bacteria commonly found in soil. neurotoxin, not very invasive. toxin binds to inhibitory interneurons which prevent release of glycine and therefore cause a constant release of acetylcholine leading to constant contraction of muscles and spastic paralysis

3. Superantigen toxins

4. enterotoxins: exotoxins whose activitiy affects the small intestine

   • cytolytic toxins
   • AB toxins
     • Chloera toxin: symptoms massive fluid loss fro the intestines resulting in severe diarrhea, dehydration and electrolyte depletion. disease states when V.cholerae is ingested from contaminated food or water. organism travels to intestine where it colonizes and secretes cholera toxin. A subunit activates adenylate cyclase which is an enzyme that converts ATP to cAMP. increased cAMP causes secretions of chloride and bicarbondate from small intestine. chang ein ion concentration causes secretion of large amounts of water.
   • Superantigen toxins