Vapor activity of 72 essential oils against a Trichophyton mentagrophytes

For practical application for vapor therapy and fumigation, the vapor activity of 72 essential oils was screened against a Trichophyton mentagrophytes, using a closed box. The fungicidal activity, expressed as the minimum fungicidal dose (MFD), was determined from the colony size, which was correlated with the inoculum size. Oils containing phenol as the major component showed the most potent vapor activity, with an MFD of 1.56 µg/ml air. This was followed by oils with aldehyde as the major component, then by those with alcohol as the major component. The vapor activities of oils containing ketone, ester, and ether/oxide components were decreased, in that order. The oils that were rich in hydrocarbon components had the weakest activity. The same tendency was observed with the components themselves. Phenols and aldehydes exhibited the highest vapor activity, followed by alcohols, ketone, ester, ether/oxide, and hydrocarbon. There was a rough correlation between the vapor activity determined by the box vapor assay and the contact activity determined by agar diffusion assay. But oils containing sesquiterpenes showed weaker vapor activity than that expected from the contact activity. Based on the activity-chemical structure relationship, the 72 oils were classified into seven functional groups.