(described by Malmsten in 1845)
Genus: Trichophyton (teleomorph: Arthroderma)
Description and Natural Habitats
Trichophyton is a dermatophyte which inhabits the soil, humans or animals. Related to its natural habitats, the genus includes anthropophilic, zoophilic, and geophilic species. Some species are cosmopolitan. Others have a restricted geographic distribution. Trichophyton concentricum, for example, is endemic at Pacific Islands, Southeast Asia, and Central America. Trichophyton is one of the leading causes of hair, skin, and nail infections in humans. Most of the Trichophyton species have teleomorphic forms and these teleomorphs are classified in the genus Arthroderma.
|Natural Habitats ofTrichophyton Species|
|mentagrophytes||zoophilic (rodents, rabbit) / anthropophilic|
|simii||zoophilic (monkey, fowl)|
|verrucosum||zoophilic (cattle, horse)|
The genus Trichophyton has several species. Most common are Trichophyton mentagrophytes, Trichophyton rubrum, Trichophyton schoenleinii, Trichophyton tonsurans, Trichophyton verrucosum, and Trichophyton violaceum. See the summary of teleomorphs, synonyms and obsolete names for the Trichophyton spp.
Several morphological and physiological characteristics are used in differentiation and identification of Trichophyton species.
|Key to the Identification of Common Species of Trichophyton|
|1.||In vitro hair perforation test positive||2|
|1′||In vitro hair perforation test negative||4|
|2.||Colonies orange buff to tan with a purple black reverse and diffusible pigment; macroconidia thick-walled, long, cylindrical to fusiform, slender, abundant, 8- to 12-celled||T. ajelloi|
|2.’||Colonies white to cream; macroconidia, when present, neither thick-walled, long, nor slender||3|
|3.||Growth occurs at 37°C, macroconidia usually rare, 2- to 5-celled, thin-walled, club-shaped to cigar-shaped; microconidia typically numerous, 1-celled, globose, solitary, along hyphae, or in clusters||T. mentagrophytes|
|3.’||Growth absent at 37°C macroconidia 2- to 6-celled, thin-walled, cylindrical; microconidia elongate to pyriform, typically 1-celled, rarely 2- to 3-celled, forming a transition from 1- to many-celled conidia||T. terrestre|
|4.||Colonies granular to woolly, often with abundant mycelium in the medium, folded, bright yellow, tan, or purplish-red with a yellowish to mahogany red reverse; macroconidia rare, clavate to cigar-shaped, thin-walled, up to 10-celled; microconidia always numerous, arising at right angles to hyphae, globose, swollen, elongate, occasionally on match stick-like conidiophores; growth enhanced by thiamine||T. tonsurans|
|4.’||Characteristics not as above||5|
|5.||Colonies rapid growing||6|
|5′||Colonies slow growing||7|
|6.||Colonies white to pink with dark blood red reverse; requires L-histidine for growth; does not require nicotinic acid||T. megninii|
|6.’||Colonies cream white to yellow, with reddish to tan centers and deep yellow or reddish brown reverse; requires nicotinic acid for growth; does not require L-histidine||T. equinum|
|7.||Colonies leathery, deep purple red, with a deep purple to violet reverse; growth enhanced by thiamine||T. violaceum|
|7.’||Colonies not deep purple red with a deep purple to violet reverse||8|
|8.||Colonies waxy, highly convoluted and heaped, cracking the agar, off-white to cream; favic chandeliers often common; conidia absent||T. schoenleinii|
|8.’||Colonies not waxy, highly convoluted, or heaped||9|
|9.||Colonies flat, woolly, or granular to cottony, white to cream with a carmine, blood red or olivaceous reverse; microconidia clavate to pyriform||T. rubrum|
|9.’||Colonies glabrous to velvety, wrinkled, raised, furrowed, or folded||10|
|10,||Reflexing hyphae present; colonies have ray-like edges, leathery, wrinkled, furrowed, raised, yellow to dark apricot with a dark yellow to brown reverse||T.soudanense|
|10.’||Reflexing hyphae absent, colonies without ray-like edges||11|
|11.||Colonies glabrous to velvety, often membranous, cream white, becoming deep tan or chocolate brown; may have a dark diffusible pigment; macroconidia unknown||T. yaoundei|
|11′||Colonies glabrous, folded, heaped, wrinkled, white, yellow to salmon with an unpigmented or salmon reverse; macroconidia 4- to 7-celled with an elongate end, formed on medium containing thiamine; thiamine and inositol (not all isolates require inositol) required for growth; growth enhanced at 37°C||T. verrucosum|
Pathogenicity and Clinical Significance
Trichophyton, Microsporum, and Epidermophyton are the causative agents of dermatophytosis and infect the hair, skin, and nails [56, 57, 657, 697, 1660, 1953, 1984, 1996]. Similar to the other two genera, Trichophyton is a keratinophilic filamentous fungus. Ability to invade keratinized tissues and the possession of several enzymes, such as acid proteinases, elastase, keratinases, and other proteinases are the major virulence factors of these fungi .
The growth rate of Trichophyton colonies is slow to moderately rapid. The texture is waxy, glabrous to cottony. From the front, the color is white to bright yellowish beige or red violet. Reverse is pale, yellowish, brown, or reddish-brown [531, 1295, 2144, 2202]. See above for the macroscopic morphology of various species.
Septate, hyaline hyphae, conidiophores, microconidia, macroconidia, and arthroconidia are observed. Chlamydospores may also be produced. Conidiophores are poorly differentiated from the hyphae. Miroconidia (also known as the microaleuriconidia) are one-celled and round or pyriform in shape. They are numerous and are solitary or arranged in clusters. Microconidia are often the predominant type of conidia produced by Trichophyton. Macroconidia (also known as the macroaleuriconidia) are multicellular (2- or more-celled), smooth-, thin- or thick-walled and cylindrical, clavate or cigar-shaped. They are usually not formed or produced in very few numbers. Some species may be sterile and the use of specific media is required to induce sporulation [531, 1295, 2144, 2202]. See above for the specific microscopic features of various species.
Septate, branched hyphae that break into chains of arthroconidia are observed. See also our histopathology page.
Trichophyton differs from Microsporum and Epidermophyton by having cylindrical, clavate to cigar-shaped, thin-walled or thick-walled, smooth macroconidia.
No special precautions other than general laboratory precautions are required.
Ketoconazole, clotrimazole, itraconazole, terbinafine, naftifine, and amorolfine are in general active in vitro against Trichophyton [725, 1399, 1887]. Terbinafine usually appears to be the most effective agent [725, 1119, 1121, 2307]. In general, isolates of Trichophyton rubrum are more susceptible to antifungal agents compared to Trichophyton mentagrophytes . The azole derivatives, Syn2869, Syn2836, Syn2903, and Syn2921 are also active in vitro against Trichophyton .
For MICs of various antifungal drugs for Trichophyton spp., see our N/A(L):susceptibility database.
Griseofulvin, once the drug of choice for treatment of dermatophytosis, is now less commonly used due to the availability of more effective and less toxic drugs . Terbinafine [114, 2485] and itraconazole [114, 524, 1007, 2485] are now commonly used in treatment of infections due to Trichophyton spp. and other dermatophytes. For treatment of tinea capitis and onychomycosis, oral therapy is usually preferred .