In Vitro Invasion of Hair by Dermatophytes
Journal of Investigative Dermatology
Dermatophytes haYe been grown in the so-called "pseudoparasitic phase" using the continuous shaking culture technic (1). This phase consists entirely of hyphae, arthrospores and chlamydospores and lacks the diverse fructification structures of the saprophytie phase. It was also shown that certain dermatophytes grown in the pseudoparasitic life phase were able to attack human nail clippings with true invasion of the nail plate by hyphae (2). The present report describes a successful attempt to
... oduce invasion of human hair in vitro by the pseudoparasitic life phase of T. mentagrophytes. MATERIAL AND METHODS The hair used was from 4 different healthy girls from j/ to S years of age in whose families tinea capitis had never occurred and who themselves were free of the disease. Tufts of scalp hair were removed with scissors and washed with water and soap. The hair was subsequently rinsed under running tap water for 6 days, immersed into 2 changes of 96% ethanol, 2 changes of ether and then dried at 37°C in sterile petri dishes. Both the medium and the inoculum of a recently isolated granular strain of T. mentagrophytes were prepared as described elsewhere (1, 2). To 3 flasks containing 100 ml of medium both inoculum and a small quantity of prepared hair were added. Controls consisted of pairs of flasks containing medium to which either hair alone or inoculum alone was added. The flasks were incubated on a rotary shaker for 46 days at 28°C. At various intervals hair and fungus pellets from various flasks were planted on glucose agar slants. After termination of the experiment some of the hair was examined microscopically in KOH preparations and the rest fixed in formalin, stained with the PAS technic and embedded in Canada balsam. REsULTS In the hair of 1 of the 4 subjects used in vitro invasion occurred. (On reexamination, this subject was again found free of tinea capitis.) Dense masses of thick hyphae were found invading the substance of the hair of this subject running parallel to its long axis (Fig. 1) . In several places the strands of hyphae formed packets of rectangular arthrospores, thus resembling the picture presented by endothrix invasion in naturally occurring tinea capitis (Fig. 2) . In other places bundles of hyphae were seen terminating inside the hair along a straight transversal line in the form of "Adamson's fringe". Often hyphae formed short lateral bud-like branches at right angles. These penetrated the cuticle of the hair with their knob-like ends or caused the cuticle to bulge, apparently in the process of penetrating it (Fig. 3) . Occasionally a single hypha was seen entering a hair from the outside by lifting part of the cuticle in a shingle-like fashion and running for various distances inside the hair parallel to its long axis.