The routine cultural identification of Microsporum ringworm of the scalp.

Tinea capitis in the United States is caused principally by Microsporum audouini and M. canis (lanosum). Identification of the responsible fungus is important in determining the prognosis. Identification of M. audouini by the usual method of planting infected hairs on agar media in a test tube requires 7 to 14 days. M. canis colonies are recognizable in 5 to 8 days. The method described below permits reduction in the time required for identification. It is recommended only for routine separation of M. canis, M. audouini and M. fulvum. We have not applied it in the differentiation of scalp ringworm due to species of Trichophyton. These latter organisms are distinctly uncommon as a cause of tinea capitis in the northeastern United States. Hairs infected with Microsporum species exhibit a characteristic bright bluegreen fluorescence. Hairs infected with the various species of Trichophyton either do not fluoresce, or exhibit a light bluish fluorescence which is readily distinguishable from that caused by Microsporum species. Method: The hair to be cultured is first viewed under the Wood's light. This permits immediate recognition of the Microsporum infected hair. If any doubt remains concerning the fluorescence, an hydroxide preparation will generally confirm the presence of the small-spored ectothrix Microsporum. The hairs are planted directly into a drop of liquid medium on a glass slide. Honey media or other Saboraud-like media are satisfactory. The routine medium used in this study was as follows: