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

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

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

5. 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
1. Nonspecific adhesion:
sometimes referred to as ‘association’ to distinguish it more clearly from specific adhesion.
Mediated by overall attractive forces between cells surfaces, mainly long-range van der Walls forces, and relatively weak hydrophobic interactions – sufficient to hold cells in close proximity despite other repulsive forces (e.g. electrostatic – net negative charge)
May also be aided by bacteria being ‘entrapped’ at host surface by materials such as mucus
KEY point about these types of interactions is that they are relatively weak and reversible.
May be sufficient to allow colonisation if adhering bacteria can multiply at a faster rate than they are removed, and this often depends on the
receptor
Weak
long-range
attractive
Repulsion reduced by:
(a) high ionic strength
(b) small diameter
easily
disrupted
Very strong
irreversible

6. 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

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

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

9. 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

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