In vitro susceptibility of dermatophytes to antifungal drugs: a comparison of two methods.

BACKGROUND

There is an evidence that some fungal strains are resistant to certain antimycotic drugs with resulting therapeutic failures. Unlike testing of antibacterial agents, the activity of these drugs against the given fungal strains is not tested routinely. The paper presented is an approach to such a procedure.

METHODS

The minimum inhibitory concentration (MIC) values obtained using the dilution method were compared with the diameters of growth inhibition zones using the disk-diffusion method. Seven antifungal drugs (griseofulvin, natamycin, naftifine, clotrimazole, bifonazole, miconazole, ketoconazole) were tested with 80 fungal strains, including Trichophyton rubrum, T. mentagrophytes, Microsporum canis, and Epidermophyton floccosum.

RESULTS

The majority of fungal strains were inhibited by griseofulvin at concentrations not exceeding 10 mg/L. The least susceptible was T. mentagrophytes. The most effective drug was naftifine, and the least effective was natamycin. Naftifine inhibited 98.75% of the strains tested at a concentration not exceeding 1.0 mg/L. An increase of the MIC value was accompanied by a decrease in the growth inhibition diameter. The relation was statistically significant.

CONCLUSIONS

T. rubrum strains are more susceptible to antifungal drugs than T. mentagrophytes. Naftifine proved to be the most effective drug in dermatophytoses. Natamycin is a useful drug against yeast-like fungi but not against dermatophytes. The disk-diffusion method of fungal susceptibility assessment yields data consistent with results obtained from the dilution method and is recommended for routine use because of its simplicity.