Transcript Slide 1
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 • Specificity of adhesion • Consequences of adhesion Overview of Bacterial Pathogenesis Sources + Transmission Entry Encounter First-line Adhesion to a surface (Invasion of tissues) Cell & tissue damage Multiply + spread Exit non-specific host defences Inflammation specific host defences Overview of interactions with host surfaces Nonspecific adhesion • overall, surface interactions • entrapment in mucin > 50 nm 10 – 20 nm Specific adhesion Weak long-range attractive Weak attractive Electrostatic repulsion Van der Walls < 2 nm Repulsion reduced by: (a) high ionic strength (b) small diameter Hydrophobic interactions < 1.0 nm Specific interactions adhesin receptor easily disrupted Very strong irreversible 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 Specific adhesion EPEC adhering to an intestinal epithelial cells Bordetella pertussis on to ciliated tracheal cell Fimbriae on surface of a human ETEC strain Strains may express > 1 distinct type of fimbriae, with different receptor specificities CS3 – thin, flexible CS1 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 ‘Complex’ Biofilms: Comprise multiple species Bacterial ‘co-aggregation’ Some species produce polysaccharides, ‘trapping’ others Example: Dental plaque