The effects of Melaleuca alternifolia (tea tree) oil on bacterial biofilms

[Truncated abstract] Biofilms are surface-associated microbial communities that occur in all environments. Clinically, biofilms can be highly detrimental, colonising abiotic surfaces such as catheters and prosthetic devices, or biotic surfaces, resulting in diseases such as urinary tract infections, dental caries and native heart endocarditis. Infections with a biofilm component are particularly difficult to treat, as cells within a biofilm exhibit resistance to the host immune system and also to antibacterial agents such as antibiotics, biocides and disinfectants. The unique nature of biofilm development, the resistance to antimicrobials, and the costly complications associated with bacterial biofilm infections has driven increased research in this area. Pressure to discover useful and novel antibiofouling agents has led to the investigation of the effects of essential oils against biofilms. The essential oil of Melaleuca alternifolia, also known as tea tree oil (TTO), has been shown to be effective as an anti-inflammatory, antibacterial, antifungal, antiviral and antiprotozoal agent. Recent studies have indicated that TTO also has potential as an antibiofilm agent. The aim of this study was therefore to investigate whether TTO could destroy mature bacterial biofilms, and whether biofilm development was inhibited in the presence of TTO. In particular, the biomass and viability of biofilms treated with TTO was assessed. Biofilms of Staphylococcus epidermidis (n=12), Escherichia coli (n=28), Stenotrophomonas maltophilia (n=1), Vibrio harveyi (n=9) and Pseudomonas aeruginosa (n=1) were grown in 96- well microtitre trays, with factors such as humidity, oxygenation and growth medium optimised for maximal biofilm biomass development.