Biofilm Growth and Retention Assays

The multi-well plate assays used to screen antifouling coatings with marine bacteria is employed to screen antimicrobial coatings. This includes the rapid determination of leachate toxicity and the use of the biomass indicator dye, crystal violet, to efficiently quantify biofilm growth and retention on the coating surfaces. In certain situations, the crystal violet dye can interact and bind with the coating material itself (i.e., without a microbial biofilm). In these instances, a variety of alternative spectrophotometric based biofilm quantification assays can be used to circumvent this issue, including additional absorbance-based dyes (i.e., alcian blue).

An antimicrobial coatings library, consisting of 30 unique coating compositions, was prepared from silanol terminated polydimethylsiloxane (PDMS) of three different molecular weights. The library was comprised of five different quaternary ammonium salts (QASs) with different alkyl chains attached with nitrogen (top left diagram). A low and high concentration of QASs was generated for each PDMS molecular weight. Visual inspection of the crystal violet stained array plates (top right picture) clearly shows an antimicrobial effect for several coating candidates. Broad spectrum activity was observed for the coatings containing the C18 QAS, as both the Gram-negative (E. coli) and Gram-positive (S. epidermidis) bacterium showed a substantial reduction in biofilm growth and retention (Bottom charts).