Inhibition of dermatophytes by optical brighteners

The aim of this study was to investigate a possible effect of optical brighteners on the growth of dermatophytes. Typical strains of Trichophyton rubrum, T. mentagrophytes, Microsporum canis and Epidermophyton floccosum were grown on agar plates containing two different brighteners of stilbenedisulfonic acid type in concentrations between 5 x 10(-5) and 1 x 10(-2) mol l-1 and their thallus diameters were compared with controls. In addition, hyphae grown with brighteners were compared with controls by fluorescence microscopy and by transmission electron microscopy. Both brighteners had a significant dose-dependent growth-suppressive effect on all dermatophytes tested, that was complete at a concentration of 10(-2) and 10(-3) mol l-1, respectively. Fluorescence microscopy of hyphae showed a pronounced fluorescence of the septal areas and a less-intense staining of the outer cell walls. Electron microscopy revealed a marked thickening and blurred contours of the cell walls grown with brighteners. These new observations relate very well to an interference of optical brighteners with the formation of normal chitin fibrils as described previously. Optical brighteners of stilbenedisulfonic acid type may be rewarding objects for the development of new antifungal agents.