Lethal photosensitisation of Staphylococcus aureus and Escherichia coli using crystal violet and zinc oxide-encapsulated polyurethane

Crystal violet and zinc oxide nanoparticles (CVZnO) were incorporated into medical grade polyurethane polymers by a two-step dipping procedure to prepare novel bactericidal surfaces. The photobactericidal activity of CVZnO polyurethane samples was tested against the Gram-positive bacterium, Staphylococcus aureus and the Gram-negative bacterium, Escherichia coli. Exposure of the polymer samples to white light induced the lethal photosensitisation of both S. aureus and E. coli. In addition, this novel system demonstrated significant antibacterial activity under dark conditions against S. aureus within 2 hours, but more remarkably, a 99.9% reduction in the numbers of E. coli within 4 hours in the dark. This is, to the best of our knowledge, the most potent ‘dark-kill’ by a light activated antimicrobial agent ever reported. The singlet oxygen quenchers, bovine serum albumin and L-histidine, and an enzyme which catalyses the decomposition of hydrogen peroxide, bovine catalase, were incorporated into the antibacterial assays to determine if the mechanism of E. coli kill involved a Type 1 or a Type 2 light-activated process