Pigment Production in the Differentiation of Trichophyton Mentagrophytes and Trichophyton Rubrum

Abstract

SUMMARY The pigment production of 50 strains of T. mentagrophytes and 40 strains of T. rubrum was studied on Sabouraud dextrose agar, potato dextrose agar, corn meal dextrose agar and ammonium chloride dextrose agar. It appeared that the appearance of pigment on the undersurface depended not only on the presence of dextrose, but also on the source of nitrogen. The strains of T. mentagrophytes examined did not produce any pigment on corn meal dextrose agar while those of T. rubrum developed the characteristic red purple color in 38 of the 40 strains examined. The other two strains produced pinkish pigmentation on the undersurface not seen on any strain of T. mentagrophytes. This observation is suggested as an aid in differentiation of the two species. T. rubrum was able to utilize dextrose, mannose and levulose for pigment production, but failed to do so with inulin, raffinose, lactose, maltose, sucrose and galactose. Pigment production by the strains studied on Sabouraud dextrose agar, potato dextrose agar and blood agar base dextrose buffered at different pH levels from pH 4.0 to 8.0 was not appreciably affected although the T. rubrum cultures on casein hydrolysate dextrose agar at pH 4.0 and on corn meal dextrose agar at pH 4.0 and 4.5 acquired only a cream to yellow pigmentation instead of red purple which appeared at other pH levels.