Lecture 2

• Overview of adhesion • Types of bacterial adhesins

• Specificity of adhesion

• Consequences of adhesion

Interactions with host surfaces II: Adhesion

Lecture 2

• Overview of adhesion • Types of bacterial adhesins

• Specificity of adhesion

• Consequences of adhesion

Interactions with host surfaces II: Adhesion

Adhesion to a surface

Multiply + spreadspecific

host defences

Cell & tissue damage

non-specific host defences

Exit

Inflammation

Overview of Bacterial Pathogenesis

EncounterEntry

First-line

Sources +Transmission

(Invasion of tissues)

Van

der

Wal

ls

> 50 nm 10 – 20 nmEl

ectro

stat

icre

puls

ion

< 2 nmHydrophobicinteractions

< 1.0 nmSpecific

interactions

easilydisrupted

Very strongirreversible

Weak long-rangeattractive

Repulsion reduced by:(a) high ionic strength(b) small diameter

Nonspecific adhesion

Wea

k at

tract

ive

adhesin

receptor

Overview of interactions with host surfaces

• overall, surface interactions• entrapment in mucin

Specific adhesion

Nonspecific adhesionNonspecific 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 adhesionSpecific adhesion

EPEC adhering to an intestinal epithelial cells

Bordetella pertussis onto ciliated tracheal cell

Fimbriae on surface of a human ETEC strain

CS3 – thin, flexibleCS1

Strains may express > 1 distinct type of fimbriae, with different receptor specificities

3. Colonize surface and form a biofilmConsequences of adhesionConsequences of adhesion

In contrast to localised ‘colonies’, some pathogens can form a spreading surface layer – a ‘BIOFILMBIOFILM’

‘Simple’ biofilm: comprises a single species

• Staphylococcus epidermidis biofilm on a catheters

• bacteria encased in a polysaccharide slime that aids attachment and protects bacteria.

‘ ‘Complex’ Biofilms:Complex’ Biofilms:

Bacterial ‘co-aggregation’ Some species produce polysaccharides, ‘trapping’ others

Example: Dental plaque

Comprise multiple species