  Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli (UPEC) to
host cells. It has been hypothesized that fimbriae can, by their ability to
uncoil under exposure to force, reduce fluid shear stress on the
adhesin-receptor interaction by which the bacterium adheres to the surface. In
this work we develop a model that describes how the force on the
adhesin-receptor interaction of a type 1 fimbriae varies as a bacterium is
affected by a time dependent fluid flow mimicking in vivo conditions. The model
combines in vivo hydrodynamic conditions with previously assessed biomechanical
properties of the fimbriae. Numerical methods are used to solve for the motion
and adhesion force under the presence of time dependent fluid profiles. It is
found that a bacterium tethered with a type 1 pilus will experience
significantly reduced shear stress for moderate to high flow velocities and
that the maximum stress the adhesin will experience is limited to ~120 pN,
which is sufficient to activate the conformational change of the FimH adhesin
into its stronger state but also lower than the force required for breaking it
under rapid loading. Our model thus supports the assumption that the type 1
fimbriae shaft and the FimH adhesin-receptor interaction are optimized to each
other, and that they give piliated bacteria significant advantages in rapidly
changing fluidic environments.
