Requisites for Successful Growth

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Requisites for Successful Growth

• Attachment
• Nutrition
• Survival from host defence
• Transmission

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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

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Bacterial Virulence Factors I Adherence

• Capsules
• Pili
• Adhesins

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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

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Bacterial Virulence Mechanisms

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

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Pili (Fimbriae)

• Composed of subunits of pilin.
• Promote adherence to other bacteria or host.
• Synonyms adhesins, lectins, evasins, aggressins.
• Fragile, often replaced.

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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.

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Bacterial Virulence Factors I Invasion

• Invasins e.g. Yersinia
• Host cell necrosis e.g. Diphtheria toxin
• Promote phagocytosis e.g. Shigella

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Bacterial Virulence Factors II Iron Adsorption

• Siderophores

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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

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Exotoxins

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

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Exotoxins I AB (i)
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Exotoxins IAB (ii)
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Exotoxins I AB (iii)
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Toxic Shock Syndrome
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Endotoxins Lipopolysaccharide

• Fever
• Leukopenia, followed by leukocytosis
• Complement activation
• Thrombocytopenia
• Coagulation
• Decreased blood circulation
• Shock
• Death