Detection and antimicrobial activity of immobilized quaternary ammonium antimicrobial monolayers on porous and non-porous surfaces

This research describes the development of novel, environmentally-friendly, non-releasing contact-active thin film coatings by immobilizing the quaternary ammonium (QA) antimicrobial group on a multitude of surfaces. Various chemical anchors based on organosilanes (i.e. textiles, silica, oxide surfaces), organosulfur comprising of thiol (noble metals), organophosphorus comprising of phosphonate and phosphonic acid (i.e. stainless steel (SS), titanium (Ti)), and catechol (Ti, SS) monolayers are employed to attach the QA antimicrobial onto metal surfaces, while benzophenone photoactive crosslinkers containing QA groups are used to coat plastic surfaces (C-H surfaces, i.e. polyethylene (PE), silicone (Si), polyvinylchloride (PVC)). Surfaces treated with covalently attached antimicrobial coatings function by killing microbes on contact, preventing surface attachment, colonization and contamination without releasing the chemical into the environment. The advantages of this method of delivery of the antimicrobial include a lower cost of application, decreased antimicrobial resistance, lower toxicity and increased environmental safety. Samples prepared by an overnight immersion in an ethanolic solution of phosphorus containing quats followed by an overnight cure at 100oC showed the highest antimicrobial reduction versus electrospray application and no curing. Short chain phosphonic acid quats and the organosilane quat were inactive on titanium. Antimicrobial activity of long chain phosphonate quats prepared by dip coating and annealing on metal surfaces (Ti, SS, Al) was tested by growth enumeration in the dry state utilizing methods developed in the Wolfaardt lab. All samples showed a 100% reduction (106 cells) of viable Salmonella, Arthrobacter, S.aureus and P.aeroguinosa after 2 hrs of contact time and maintained their activity over 24 hrs versus the uncoated controls. To demonstrate the phosphonate quats were truly immobilized, Ti samples from the first trial were washed in distilled H2O, dried, and re-innoculated with 106 Anthrobacter colonies. No visible colonies of Anthrobacter remained after 2 hrs of contact time with the Ti surfaces indicating a contact killing mechanism at play.