Germination and initial growth of Microsporon audouinii from infected hairs

The dermatophytes

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Microsporum, and Trichophyton. Species capable of reproducing sexually belong in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophilic (soil associated), zoophilic, and anthropophilic. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, hair, and nails) but are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Chronic dermatophytosis is mostly caused by Trichophyton rubrum, and there is some evidence that mannan produced by this fungus suppresses or diminishes the inflammatory response. Since dermatophytes cause a communicable disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and tests for identification are also presented. Genetic studies have led to an understanding of incompatibility mechanisms, pleomorphism and variation, resistance to griseofulvin, and virulence. Molecular biology has contributed to our knowledge of the taxonomy and phylogenetic relationships of dermatophytes.

Formation and germination of fungal arthroconidia

A large variety of fungi are known to produce asexual spores known as arthroconidia. These propagules are formed by segmentation of existing hyphae and may form by several mechanisms. The specific processes of formation may lead to acropetal, basipetal, or random formation of endoarthroconidia or exoarthroconidia. The development of arthroconidia is a survival response to the depletion of nutrients or other environmental stresses and, in at least one case, is accompanied by the excretion of high levels of antibiotics. Arthroconidia are generally not as resistant to physical factors as are other fungal reproductive structures and are also susceptible to a variety of antibiotics and disinfectants. Arthroconidia are produced by some medically important fungi and in some cases, such as coccidioidomycosis, they are the principal means of dissemination. Germination of arthroconidia in complex media generally does not require specific "activation" events.

Monitored environment system to control cell growth, morphology, and metabolic rate in fungi by oxidation-reduction potentials

A device for the adjustment, maintenance, and monitoring of a desired oxidation-reduction potential in a liquid environment is described. The filamentous species, Penicillium lilacinum and Trichophyton schoenleinii, and the dimorphic species, Histoplasma capsulatum, developed budding yeastlike cells when grown in a liquid medium with a low oxidation-reduction potential. When the organisms were inoculated into fresh medium, they returned to the filamentous condition as the oxidation-reduction potential was restored to a more positive (oxidizing) environment.