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J. J. Merritt, S. Zhang, D. Miller, S. C. G. Tseng; Anti-Microbial Effects of Tea Tree Oil. Invest. Ophthalmol. Vis. Sci. 2007;48(13):771.
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Recently we have reported that weekly lid scrub with 50% tea tree oil (TTO) is effective in eradicating ocular infestation of demodex. We would like to evaluate in vitro activity of TTO against common ocular pathogens.
Serial dilutions (0, 3.13%, 6.25%, 12.5%, 25%, 50%, and 100%) of TTO were prepared in Mac Nut Oil. Ocular isolates (Methicillin resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Fusarium species, and Acanthamoeba species) were grown overnight in trypticase soy broth or Page saline and adjusted to 107 cfu/ml. Aliquots (100 µl) of each dilution were distributed into wells of a 96 well titer plate for each isolates. 100 µl of each ocular isolate was then placed into each well, and each isolate was evaluated in triplets. Plates were incubated in the dark at 36 oC for 18-24 hours (bacteria) and 48 hours for fungi and Acanthamoeba. Pseudomonas aeruginosa 27853 and Staphylococcus aureus 29213 were also added as controls. The Minimal inhibitory concentration was read as the first well that demonstrated no growth. All clear (no growth) wells were subcultured to brain heart infusion agar to determine the minimal bactericidal concentration.
TTO demonstrated in vitro activity against all ocular isolates tested. MIC ranged from 3.13% to ≥ 25%. Further studies are under way to test its anti-microbial activity against additional organisms using different dilution media for each organism over a longer range of incubation (e.g., 25 C, 3-7 days). These results will help us consider topical TTO as an adjunctive measure to control microbial flora and load in the ocular surface.
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