Methods: Twenty three oils and five major oil component compounds were tested for anti-candida activity using a combination of disc and well diffusion, and agar and broth dilution assays. Three typed strains of Candida; C.albicans GDH2346, C.tropicalis MMU1, and C.krusei NCYC993 were used to screen all oils and components for potential activity. Oils were initially tested at 95-98% concentration (as supplied). Sterile filter paper discs (6mm) soaked in each oil/component were placed onto lawns of Candida on Sabouraud Dextrose agar. Oils producing zones of inhibition ≥15mm were tested at 2% concentration. Oils demonstrating zones ≥15mm at 2% were tested against 40 oral candida isolates, including C.albicans, C.tropicalis and C.guillermondii. Oils demonstrating potent anti-candida activity were also tested against selected potential pathogens that may come into contact with denture surfaces, particularly during handling and rinsing including Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Individual MICs were determined for the most potent anti-candida oils. Combinations of the most effective oils were tested and MICs of the most potent combinations determined.
Results: Ten of the 23 oils displayed zones of inhibition ≥15mm against at least one Candida.spp tested, the most active being cinnamon bark, oregano green, thyme, peppermint and lemongrass. Although differences were observed in susceptibility between Candida.spp (C. albicans most and C.krusei least sensitive), this was not significant. Lemongrass showed the broadest anti-microbial properties against all microorganisms tested. Of all potential pathogens tested, Candida.spp had significantly greater sensitivity to the oils than E.coli and Ps.aeruginosa (F=6.45, p<0.001). Conclusion: Candida demonstrated greater susceptibility to oils than tested bacterial species. Since Candida have been shown to be less susceptible to oral hygiene products, this finding indicates the potential for use of oils in anti-candida products.