Trichophyton rubrum (Castellani) var. flava, var. nova. A yellow pigment forming Trichophyton rubrum

Rapid method for differentiation of Trichophyton rubrum, Trichophyton mentagrophytes, and related dermatophyte species

Bromocresol purple-milk solids-glucose medium, proposed by Fischer and Kane in 1971 (Mycopathol. Mycol. Appl. 43:169-180, 1971) as an aid in the rapid determination of Trichophyton rubrum and Trichophyton mentagrophytes, was evaluated across a wide range of isolates to determine its accuracy and efficacy in the clinical laboratory. Results showed that it facilitated accurate determination of typical and atypical isolates of both species and also permitted the rapid identification of other closely related and similar species. Identification of all dermatophyte species tested was possible within 7 to 10 days. Occult contamination of isolates by antibiotic-resistant bacteria did not hinder identification.

The routine use of modified Borelli's lactritmel agar (MBLA)

The original formula of Borelli's lactritmel agar (BLA)(3) which contains wheat flour, milk and honey, has been modified by replacing the wheat flour with dehydrated Bacto Corn Meal Agar (Difco) and by slightly altering the concentrations of the milk and honey. The modified medium (MBLA) is less turbid, less particulate, and easier to prepare than BLA. Although Trichophyton rubrum usually produces a wine-red pigment with BLA, most strains initially produce a yellow pigment, with the red pigment developing later. The corn meal in MBLA reduces this tendency and stimulates the early formation of deep wine red pigment, MBLA enhances sporulation of dermatophytes and various fungi which fail to sporulate on other media, and maintains characteristic growth without developing pleomorphic degeneration. It has been used routinely since 1972 as a reliable aid to the differentiation of T. rubrum and T. mentagrophytes. Since 1975 selective MBLA has been used as a routine primary isolation medium for dermatophytes, and has proved to be most useful.