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Requisites for Successful Growth

Requisites for Successful Growth. Attachment Nutrition Survival from host defence Transmission. Virulence Factors. Factors which promote infection and which contribute to disease Studied with mutants Are multifactorial Consist of: Factors promoting colonization and invasion

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Requisites for Successful Growth

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  1. Requisites for Successful Growth • Attachment • Nutrition • Survival from host defence • Transmission

  2. Virulence Factors • Factors which promote infection and which contribute to disease • Studied with mutants • Are multifactorial • Consist of: • Factors promoting colonization and invasion • Factors which are pathogenic

  3. Bacterial Virulence Factors I: Adherence • Capsules • Pili • Adhesins

  4. Capsules • Present in some gram negative and positive bacteria. • May be composed of protein or polysaccharide layers. • Is poorly antigenic and anti-phagocytic • Can act as a barrier to toxic hydrophobic molecules such as detergents. • Can promote adherence to other bacteria or cell surfaces

  5. Bacterial Virulence Mechanisms • Adherence • Invasion • By-products of growth (gas, acid) • Toxins • Superantigen • Immune evasion • Resistance to antibiotics

  6. Pili (Fimbriae) • Composed of subunits of pilin. • Promote adherence to other bacteria or host. • Synonyms: adhesins, lectins, evasins, aggressins. • Fragile, often replaced.

  7. Adhesins • Adherence mediated by lectin activity. • Allow attachment to vulnerable membranes such as surfaces of the respiratory, GI and urogenitary tract as well as dentine. • Can alter structural properties of host cell membrane by signal transduction and induction of actin rearrangement (EPEC intimin) to enhance binding.

  8. Bacterial Virulence Factors I: Invasion • Invasins e.g. Yersinia • Host cell necrosis e.g. Diphtheria toxin • Promote phagocytosis e.g. Shigella

  9. Bacterial Virulence Factors II: Iron Adsorption • Siderophores

  10. Toxins • Toxic byproducts of bacterial growthe.g. acids, gas, proteases • Toxins • Endotoxins e.g. LPS • Exotoxins e.g AB toxins • Toxins vs Toxoids • Heat labile vs Heat resistant • Ineffectiveness of antibiotics

  11. Exotoxins • AB. e.g. Shigella dysenteriae, C. tetani, V. cholerae. • Cell Membrane Disruption. e.g. C. perfringens • Superantigens. e.g. S. aureus

  12. Exotoxins I: AB (i)

  13. Exotoxins I:AB (ii)

  14. Exotoxins I: AB (iii)

  15. Toxic Shock Syndrome

  16. Endotoxins: Lipopolysaccharide • Fever • Leukopenia, followed by leukocytosis • Complement activation • Thrombocytopenia • Coagulation • Decreased blood circulation • Shock • Death

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