Antibacterial activity of quaternary ammonium monomers in solution and in non leaching coatings

The retention of pathogen bacteria on contact surfaces increases the risk of cross-contamination and diseases transmission in industrial, hospital and domestic environments. Functional coatings containing biocides can endow antimicrobial properties to the surfaces in order to obtain free pathogen surfaces. The chemical bonding to the coating structure of monomers containing bioactive groups is a successful method to prevent the residual toxicity caused by a biocide release into the surroundings. In this study the antimicrobials activities of acrylic quaternary ammonium monomers (QAMs) in solution were investigated and compared with the antimicrobials activities of coatings obtained by insertion of QAMs into a urethane diacrylate structure by UV copolymerization. The effect of three dimethyl alkyl QAMs with alkyl chain of 2 (C2), 8 (C8) and 16 (C16) carbon atoms were investigated against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Listeria monocytogenes (L. monocytogenes). Figure 1 shows the reduction of the number of viable cells observed for cells in suspensions or attached on stainless steel surfaces after contact with QAMs solution or with coatings containing QAM moieties. The inhibitory effect differs with regard to the alkyl chain. The QAM with the shortest chain shows a limited effect towards cell suspension, while the C8 and C16 QAMs show high efficacy A survival decrease higher that the detection limit (> 6 log units) on L.monocytogenes, S.aureus is observed. However, the reduction grade was markedly lower on cells layered on stainless steel. Surprisingly, the C16 QAM bonded to the polymer structure lost the antibacterial activity. Results demonstrate that the C8 QAM modified coating could be a promising antimicrobial material but concentrations higher than 1% should be tested to achieve higher growth inhibition.