In a living host the selectivity of dermatophytes for the keratin-containing dead outer structures of the skin is so extreme as to engender the terms keratinophilic and necrophilic for these organisms. The present study provides data to suggest that there are humoral factors which ordinarily bar invasion by dermatophytes but that under appropriate circumstances the organisms will readily invade living nonkeratinous skin.
The superficial habitat of the ringworm fungi is not a result of favorable nutritional factors in the keratinous layers. In the test tube, dermatophytes grow as vigorously in other media as they do in one containing only keratinous materials, such as powdered callus, or hair or nail clippings. Jacobs and Lorincz found little difference between growth of dermatophytes on the corium side or the cornified side of buttons of excised and killed human skin.12 Nonetheless, even when the organisms gain entrance
BLANK H, SAGAMI S, BOYD C, ROTH FJ. The Pathogenesis of Superficial Fungous Infections in Cultured Human Skin. AMA Arch Derm. 1959;79(5):524–535. doi:10.1001/archderm.1959.01560170022005
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