Value of Three Types of Tests by Multiple Media Flask Culture Method to Differentiate Trichophyton rubrum and T. mentagrophytes

Abstract

One hundred forty-six isolates of T. rubrum and 93 isolates of T. mentagrophytes were subjected to urease test, in vitro hair perforation test with solid medium and red pigment production test by multiple media flask culture method. Evaluations were made by culturing fungi on small square pieces of Christensen's urea agar, 0.05% yeast extract agar with human hair, Sabouraud dextrose agar, oatmeal agar and oatmeal with 1% dextrose agar medium.
The urease test was negative in 71.2% of the isolates of T. rubrum, indeterminate in 27.2% and positive in 1.4% and was negative in 4.3% of T. mentagrophytes, indeterminate in 19.4% and positive in 76.3%. In vitro hair perforation test was negative in 97.9% and positive in 2.1% of T. rubrum, and was negative in 20.4% and positive in 79.6% of T. mentagrophytes. Red pigment production test was positive in 24% of T. rubrum, while it was negative in all of the isolates of T. mentagrophytes. All isolates that showed negative or indeterminate in the urease test and negative in the in vitro hair perforation test were T. rubrum. And all those that showed positive in the urease and in vitro hair perforation tests were T. mentagrophytes.
The combination of urease test and in vitro hair perforation test seems very useful to distinguish T. rubrum from T. mentagrophytes. The high rate (76.3%) of clear distinction of these two fungi achieved by this combination indicates the reliability of the culture method for identification of dermatophytes.