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Unformatted text preview: Staphylococcal Pathogenesis a) Staphylococcal Food Poisoning 1. Transmission/Entry: food is contaminated with S. aureus or the toxin(enterotoxin) it produces and is consumed by host. 2. Overcomes host’s Innate defenses on the digestive system • Saliva • Bile • Enzymes • Low pH of the stomach • mucus 3. Attachment in the epithelial cells of the stomach • Teichoic acid – mediate adherence to mucosal cells by binding to fibronectin 4. The host mounts an inflammatory response • Purpose of the Inflammatory Response: Make a localized response to infection, wall off infected are, deliver phagocytes and soluble proteins to infected area, kill and prevent the spread of the pathogen. • Major events: Vasodilatation and increased vasopermeability of blood vessels in the area with the leakage of high protein exudate containing complement and coagulation cascade proteins followed by extravasation of phagocytic WBCs to site of infection. • Role of Complement and Phagocytosis 1. Complement – alternative pathway is activated in order to opsonize the bacteria with C3b, produce C3a and C5a which acts as chmotaxins and anaphylatoxins to contribute to inflammation. 2. Phagocytosis – The professional phagocytes, the neutrophils, and macrophages try to phagocytose and kill the pathogen ( S. aureus ) 5. S. aureus Resistance to host inflammatory response • Complement 1. Polysaccharide capsule 2. Protein A – binds antibody upside down and prevent opsonization 3. Clumping Factor – causing clumping of plasma and deposition of fibrin protects it from complement • Phagocytosis 1. Polysaccharide capsule resists phagocytosis 2. Alpha toxin – kills phagocytes by lysing cell membranes and lysosomal membranes 3. Beta Toxin – kills body cells and incoming phagocytes 4. Clumping Factor (Bound Coagulase) - causing clumping of plasma and deposition of fibrin protects it from phagocytosis 6. Spreads through tissue • The bacterial continues to multiply and spread through tissue using: 1. Staphylokinase – lyses blood clots to promote invasion and spread 2. Hyaluronidase - breaks down hyaluronic acid in host tissue 3. DNAse – breaks down viscous DNA 7. Spread into bloodstream • They enter the bloodstream through lymphatic system channels and resist the fixed macrophages of the RES which attempts to phagocytose them because their Polysaccharide capsule and Protein A are antiphagocytic 8. Production of Enterotoxins (Serotypes A to F) • This is responsible for the vomiting and diarrhea. • Act directly on neural receptors in the gastrointestinal tract which stimulates vomiting. 9. Role of Adaptive Immunity • Host mounts a hummoral immune response 1. Phagocytes will phagocytose and kill pathogen 2. Complement a. C3b is made to opsonize the pathogen and will lead to phagocytosis and killing of pathogen b. Antibodies are produce to neutralize toxins made by pathogen such as Enterotoxins, alpha toxins, and beta toxins 10. Exit b) An Abscess in an extremity following a knife wound...
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- Fall '09
- The Digestive System, S. aureus, inflammatory response, phagocytes