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Lecture 2

Lecture 2. Interactions with host surfaces II: Adhesion. Overview of adhesion Types of bacterial adhesins Specificity of adhesion Consequences of adhesion. Lecture 2. Interactions with host surfaces II: Adhesion. Overview of adhesion Types of bacterial adhesins

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Lecture 2

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  1. Lecture 2 Interactions with host surfaces II: Adhesion • Overview of adhesion • Types of bacterial adhesins • Specificity of adhesion • Consequences of adhesion

  2. Lecture 2 Interactions with host surfaces II: Adhesion • Overview of adhesion • Types of bacterial adhesins • Specificity of adhesion • Consequences of adhesion

  3. Overview of Bacterial Pathogenesis Sources + Transmission Entry First-line Encounter Adhesion to a surface non-specific host defences (Invasion of tissues) Inflammation Cell & tissue damage specific host defences Multiply + spread Exit

  4. Overview of interactions with host surfaces • Nonspecific adhesion • Specific adhesion • overall, surface interactions • entrapment in mucin > 50 nm 10 – 20 nm < 2 nm < 1.0 nm Hydrophobic interactions Specific interactions Electrostatic repulsion Van der Walls Weak attractive adhesin receptor Weak long-range attractive easily disrupted Very strong irreversible Repulsion reduced by: (a) high ionic strength (b) small diameter

  5. Nonspecific adhesion • Weakly adhering bacteria - easily removed by physical shear forces or washing • May allow colonisation of surfaces not subject to strong physical/washing forces (e.g. skin, vagina) • Not sufficient to colonise e.g. urinary tract, small intestine, etc

  6. Specific adhesion EPEC adhering to an intestinal epithelial cells Bordetella pertussis on to ciliated tracheal cell

  7. Fimbriae on surface of a human ETEC strain • Strains may express > 1 distinct type of fimbriae, with different receptor specificities CS3 – thin, flexible CS1

  8. Consequences of adhesion 3. Colonize surface and form a biofilm • In contrast to localised ‘colonies’, some pathogens can form a spreading surface layer – a ‘BIOFILM’ • bacteria encased in a polysaccharide slime that aids • attachment and protects bacteria. • ‘Simple’ biofilm: comprises a single species • Staphylococcus epidermidis • biofilm on a catheters

  9. ‘Complex’ Biofilms: • Comprise multiple species • Bacterial ‘co-aggregation’ • Some species produce polysaccharides, ‘trapping’ others Example: Dental plaque

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