Antimicrobial efficacy of silver ions in combination with tea tree oil against Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans

Tea tree oil (TTO) and silver ions (Ag+), either alone or in combination with other antimicrobial compounds, have been used in the treatment of topical infections. However, there appears to be little data on the efficacy of TTO combined with silver in the absence of any other agents. TTO and Ag+ were added, alone and in combination, to suspension cultures of Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Treatment of these cultures with TTO and Ag+ at sub-minimal lethal concentrations resulted in an enhanced loss of viability compared with treatment with individual agents. The order of sensitivity to the combined agents was P. aeruginosa > S. aureus > C. albicans. The fractional lethal concentration index (FLCI) showed that these combinations of TTO and Ag+ exerted a synergistic effect against P. aeruginosa (FLCI = 0.263) and an indifferent effect against S. aureus and C. albicans (FLCI = 0.663 and 1.197, respectively). The results indicate that combining these antimicrobial agents may be useful in decreasing the concentration of antimicrobial agents required to achieve an effective reduction in opportunistic pathogenic microorganisms that typically infect wounds.