Abstract
The pattern of invasion of human hair in vitro by the dermatophyte Microsporum gypseum was studied by transmission and scanning electron microscopy. Mycelia that invaded the hair cortex through the edge of cuticles showed a flattened "frond" growth in contrast to the filamentous form seen on ordinary laboratory media. The frond cells were characterized by the presence of vesicles formed by invaginations of plasmalemma, and lomasomes were prominent in the region adjacent to the hard keratinized tissue of the hair cortex being degraded as well. The initial perforating organ, which originated from the frond mycelium, appeared as an enlarged spherical cell which integrated with the laterally branched hyphae, as revealed by analysis of a three-dimensional model reconstructed from a series of sections. The fully developed perforating organ consisted of a column of wide and short cells which penetrated perpendicularly through the hair cortex. Through the medulla the filamentous hyphae had grown profusely in a longitudinal direction. Our studies confirm earlier light microscope observations and provide new ultrastructural details on the development of the eroding frond and the perforating organ.