Nevertheless, even with an order of magnitude
correction to our estimated stresses, the FOS values are still
quite high (33–5,500). Thus, it appears that bacterial biofilms
are designed to withstand extreme forces and not just typical or
average applied forces. However, more research is needed to
elucidate the full range of stresses experienced by the biofilms
grown for strength testing. Perhaps, experimental techniques
such as particle image velocimetry or modeling approaches such
as computational fluid dynamics could aid in these efforts.
Finally, it could also be argued that the strength of the
biofilm matrix is not dictated by the applied fluid shear but is
merely coincidental because the EPS composition and density
are dictated by other purposes such as serving as a defense
from biocides17 or as a cache of stored food.18,19 If this were
the case, one would not expect the strength to increase with
fluid shear. Nevertheless, correlations between strength and
the fluid shear experienced by the biofilm during growth have
been reported in the literature.20–22 This indicates that higher
shear conditions actually select for stronger biofilms. If this
is the case, then either the bacteria in the biofilm sense the
increased shear and respond by changing EPS composition,
increasing EPS density, or both or the weak EPS and the
bacteria that secreted them are simply washed away leaving
the stronger biofilm formers behind