In vitro activity of Melaleuca alternifolia (tea tree) oil against bacterial and Candida spp. isolates from clinical specimens

This study investigates the in vitro activity of tea tree oil (TTO) against a range of wild strains of microorganisms isolated from clinical specimens of leg ulcers and pressure sores. The antimicrobial effectiveness of TTO i s determined in terms of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBQ or minimum fungicidal concentration (MFC). The isolates include methicillin-resistant Staphylococcus aureus (MRSA), S . aureus, faecal streptococci, P-haemolytic streptococci, coagulase-negativ e staphylococci, Pseudomonas spp. and coliform bacilli. Eleven Candida spp. isolates from skin and vaginal swabs also are tested. Using an agar diluti on assay, the MICs of TTO in 88 out of 90 isolates was 0.5-1.0% (v/v), whil st with P. aeruginosa it was >2% (v/v). A broth microdilution method was us ed to determine MIC and minimum cidal concentration (MCC) of 80 isolates. I n 64 isolates, TTO produced an inhibitory and cidal effect at 3% and 4% (v/ v), respectively. S. aureus and Candida spp. were the most susceptible to T TO, with MICs and MBCs of 0.5% and 1 %, respectively. P. aeruginosa and the faecal streptococci isolates, with MICs and MBCs of >8%, were resistant to TTO.