Abstract:

Objective　To report a case of black-dot ringworm caused by Trichophyton tonsurans in a 3-year-old girl. Methods　Lesional hair was obtained from the patient and subjected to direct microscopic examination as well as culture. Subsequently, the isolate underwent morphological, biochemical and molecular biology identification. The extracellular enzymatic activity of the isolate was analyzed. Results　Microscopy revealed that the hair shaft was filled with fungal spores. Typical colony of the isolate was grayish-white with downy appearance. Slide culture showed centipede-like, lateral, rod-shaped microconidia. Urease test was positive. The amplification of ribosomal DNA （rDNA） ITS domains by PCR produced a 687 bp-sized fragment which had a 100% homology with the sequences of several Trichophyton tonsurans strains in the GenBank database. The extracellular enzymatic activity analysis showed an increase in the activity of alkaline phosphatase, acid phosphatase, esterase （C4）, β-glucosidase, leucine arylamidase, N-acetyl-β-glucosaminidase and α-mannosidase. Conclusions　The pathogenic fungus is identified as Trichophyton tonsurans based on morphological and biochemical features as well as sequence of the ITS region of rDNA, and the child was diagnosed with black-dot ringworm.

Key words: Black-dot ringworm, Trichophyton tonsurans, extracellular enzymatic activity