Clinical mycology remains more of a descriptive art than an analytical science. You may find that the identification of fungi requires a greater development of your visual acuity than was necessary in bacteriology. There are also fewer biochemical tests available to aid in the differential identification of fungi. As a result you will spend considerable time in the laboratory visually examining fungal cultures in slide culture preparations. You will identify characteristic fungal structures by observing colonial growth both macroscopically and microscopically.
A thorough understanding of correct fungal terminology is of critical importance. You may find that the terms used to describe fungi are unusual, at times redundant, and often very confusing. We have attempted to simplify the jumbled jargon by providing you with the following list of terms that will be used most often in the laboratory section of this course. Although most of these terms have already been introduced in the lecture notes, they have been included in the laboratory manual as well.
Arthrospores - asexual, thick-walled spores formed by hyphal septation. Arthrospores are released only by fragmentation of the hyphae. The barrel-shaped arthrospores of Coccidioides immitis are the infectious stage of coccidioidomycosis.
Chlamydospore - thick, double-walled, resistant, asexual spores that form as enlarged segments either within (intercalary) or at the tip (terminal) of hyphae. Often form under specific nutritional conditions where other spores do not form.
Conidia (singular = conidium) - asexual spores borne externally on hyphae or on a conidiophore; may be unicellular (microconidia) or multicellular (macroconidia).
Conidiophore - the specialized hyphal stalk on which conidia develop either singly or in clusters.
Dematiaceous - dark-colored (green, brown, or black) fungi whose hyphae are pigmented. Both the top and the underside of the mycelia will be dark.
Dimorphic - Having both a yeast and a mold (mycelial) form. Many of the systemic fungal pathogens are dimorphic.
Ectothrix - Dermatophytes that produce a sheath of arthrospores on the external surface of the hair shaft.
Endothrix - Dermatophytes that produce arthrospores within the hair shaft.
Endospore - Asexual spores formed within a cell (as in the spherule of Coccidioides immitis).
Geophilic - Refers to fungi whose natural habitat is the soil. Use of this term is generally restricted to certain Dermatophytes (e.g. Microsporum gypseum).
Germ-tube - The initial hyphal outgrowth of a germinating spore or yeast; especially important for
identification of Candida albicans.
Mycelium (Collective term for Hyphae/Hypha)- the intertwined mass of hyphae that forms the mold colony.The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi The vegetative mycelium is composed of those hyphae that adhere to the substrate and absorbs nutrients. The aerial mycelium is composed of those hyphae that grow up from the surface and support the spores.
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| Mycelium |
Pseudohyphae - chains of successively budding yeast cells that have complete cell walls, but have not detached from one another.
Rhizoid - rootlike branched hyphae which anchor the mycelium to the substrate; characteristic of certain Zygomycetes (Rhizopus and Absidium).
Septate - Cross-walls (septae) that divide hyphae into segments. If there are few or no cross-walls the hyphae are considered to be aseptate.
Sporangia (singular = sporangium)- spherical sack within which asexual spores (sporangiospores) form by progressive cytoplasmic cleavage.
Sporangiophore- specialized hyphal stalk which bears sporangia.
Sporangiospores-small spores contained within sporangia
Sterigmata- branched apex of a conidiophore that bears conidia
Vesicle- swollen apex of a conidiophore that bears conidia
Zoophilic- refers to certain Dermatophytes that predominantly infect animals as opposed to humans
(ex: Microsporum canis).
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