In addition, the estimated shear stresses experienced
by the three biofilms during growth were 0.07 Pa, 0.18 Pa,
and 1.9 Pa, respectively. Thus, the cohesive strengths of the
biofilms are four to five orders of magnitude greater than the
shear stress experienced during growth (Fig. 2).
Engineering designs of structures such as bridges and
buildings incorporate a factor of safety (FOS).13 The FOS is
defined as a ratio of the structural strength (eg, of the building
or bridge) to that of the applied loads. A biofilm FOS