Antibacterial activity studies of plasma polymerised cineole films

Costs associated with bacterial infections in medical devices exceed $US 30 billion each year in the United States alone due to device revisions and patient treatment. Likewise, in 2012-2013, 126 surgical bacterial infections cost a single Australian state over $AUD 5 million. In the search for coatings that can prevent bacterial attachment and reduce medical and human costs, a number of studies have explored the application of antibacterial and anti-fungal essential oils. Traditionally the antibacterial properties of tea tree oils have been linked to their major component terpinen-4-ol, with little focus on the second component, 1,8-cineole. In this study we explore the antibacterial behaviour of solutions of cineole and demonstrate its ability to significantly reduce Escherichia coli viability in solution. However, one of the challenges with essential oils is their limited reactivity and solubility, creating a significant limitation for translating these antibacterial oils into coatings for medical devices. Previous studies have shown that plasma polymerised thin films can be produced from 1,8-cineole (ppCo), though it is unknown if the antibacterial activity can be retained. Herein, we report the behaviour of ppCo films when exposed to different solvents, and the interaction of these films with two bacteria (Escherichia coli and Staphylococcus aureus) commonly related to the failure of medical devices. While a reduction in bacterial attachment was observed onto both the ppCo film and the control hydrophobic surface, only the ppCo coatings resisted biofilm formation after 5 days of incubation with Escherichia coli. Additionally, ppCo films were shown to be non-adherent and non-cytotoxic to mammalian fibroblast. The combination of these two findings suggests that while the ppCo films retained part of the antimicrobial activity of the cineole oil, any leachables that may be released from the coating are also not cytotoxic or cell disruptive to mammalian cells. These coatings present a promising approach toward creating biocompatible antimicrobial coatings from Australian essential oils.