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 >Factors which are pathogenic

Bacterial Virulence Factors I: Adherence Capsules Pili Adhesins

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

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

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

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.

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

Bacterial Virulence Factors II: Iron Adsorption Siderophores

Toxins Toxic byproducts of bacterial growth e.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

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

Exotoxins I: AB (i)

Exotoxins I:AB (ii)

Exotoxins I: AB (iii)

Toxic Shock Syndrome

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