  Simulations of tethered cells in viscous sub-layers are frequently performed
using the Stokes drag force, but without taking into account contributions from
surface corrections, lift forces, buoyancy, the Basset force, the cells finite
inertia, or added mass. In this work, we investigate to which extent such
contributions influence, under a variety of hydrodynamic conditions, the force
at the anchor point of a tethered cell and the survival probability of a
bacterium that is attached to a host by either a slip or a catch bond via a
tether with a few different biomechanical properties. We show that a
consequence of not including some of these contributions is that the force to
which a bond is exposed can be significantly underestimated; in general by
~32-46 %, where the influence of the surface corrections dominate (the parallel
and normal correction coefficients contribute with ~5-8 or 23-26 %,
respectively). The Basset force is a major contributor, up to 20 %, for larger
cells and shear rates. The lift force and inertia contribute when cells with
radii >3 micrometer reside in shear rates >2000 1/s. Buoyancy contributes
significantly for cells with radii >3 micrometer in shear rates <10 1/s. Since
the lifetime of a bond depends strongly on the force, both the level of
approximations and the biomechanical model of the tether significantly affect
the survival probability of tethered bacteria. For a cell attached with a
FimH-mannose bond and an extendable tether in a shear rate of 3000 1/s,
neglecting the surface correction coefficients or the Basset force can imply
that the survival probability is overestimated by more than an order of
magnitude. This work thus shows that in order to quantitatively assess
bacterial attachment forces and survival probabilities, both the fluid forces
and the tether properties need to be modeled accurately.
