Bacterial Footprints in Elastic Pillared Microstructures

Soft substrates decorated with micropillar arrays are known to
be sensitive to deflection due to capillary action. In this work, we demonstrate
that micropillared epoxy surfaces are sensitive to single drops of bacterial
suspensions. The micropillars can show significant deformations upon
evaporation, just as capillary action does in soft substrates. The phenomenon
has been studied with five bacterial strains: S. epidermidis, L. sakei, P.
aeruginosa, E. coli, and B. subtilis. The results reveal that only droplets
containing motile microbes with flagella stimulate micropillar bending, which
leads to significant distortions and pillar aggregations forming dimers, trimers,
and higher order clusters. Such deformation is manifested in characteristic
patterns that are left on the microarrayed surface following evaporation and
can be easily identified even by the naked eye. Our findings could lay the
ground for the design and fabrication of mechanically responsive substrates,
sensitive to specific types of microorganisms.