Evaluation of the Viability of Trichophyton mentagrophytes

Using Neutral Red Staining in vitro

Abstract

To elucidate discrepancies in the results obtained by direct microscopic examination and subsequent culture, the viability of Trichophyton mentagrophytes was evaluated by neutral red staining in vitro. When the number of neutral red staining-positive T. mentagrophytes treated with the antifungal agent (NND-318) were compared with the number of viable T. mentagrophytes obtained by subsequent culture on Sabouraud's dextrose agar, a strong positive correlation was found between the two sets of numbers.
This finding sugests that neutral red staining is a useful method for evaluating the viability of T. mentagrophytes in vitroand that number of fungal elements obtained by direct microscopic examination includes the number of dead T. mentagrophytes treated with antifungal agents. Therefore, the effectiveness of antifungal drugs should not be evaluated by the existence of fungal elements in skin scales using KOH direct microscopic examination, but should be evaluated by those viability using culture or neutral red staining.