RESUMO
We tested the Australian tea tree oil [Oil of Melaleuca] for its antimicrobial activity on standard and clinical isolates of bacteria and fungi using a serial agar dilution method. The fourteen standard bacterial and fungal isolates were inhibited in an oil concentration range of 1-8 mg/ml except for Pseudomonas aeruginosa which was resistant to more than 128 mg/ml. The minimum inhibitory concentrations of the oil against 66 clinical bacterial isolates representing 14 bacterial species showed that the 27 Gram positive bacteria were more sensitive to the oil with average MIC values of 1.2 to 12 mg/ml. Gram negative bacteria [39 isolates] were less sensitive than Gram positive bacteria since 21 isolates were resistant to more than 10 mg/ml. The MIC values of the oil against 75 clinical fungal isolates representing 8 different filamentous fungi and yeasts showed that the fungi were more sensitive than Gram positive and Gram negative bacteria. The oil has bactericidal and fungicidal activity but its clinical usefulness needs further evaluation