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Category: Clinical Microbiology
Trichophyton, Microsporum, Epidermophyton, and Agents of Superficial Mycoses, Page 1 of 2
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Superficial fungal infections constitute some of the most common infectious conditions and include dermatophytosis (tinea corporis, tinea capitis, tinea pedis, and tinea unguium) and pityriasis versicolor, as well as rarer disorders like tinea nigra and black and white piedra. The etiologic agents of dermatophytosis are classified, along with some nonpathogenic relatives, in three genera: Trichophyton, Microsporum, and Epidermophyton. Dermatophytes are keratinophilic fungi that are capable of invading the keratinous tissues of living animals. They are grouped into three categories based on host preference and natural habitat: (i) anthropophilic species almost exclusively infect humans, with animals being rarely infected; (ii) geophilic species are soil-associated organisms that can occasionally cause infections in humans and other animals; and (iii) zoophilic species are essentially pathogens of nonhuman mammals, although animal-to-human transmission is not uncommon. This chapter describes the taxonomy, epidemiology, transmission, and clinical significance of dermatophytes. The methods of diagnosis of dermatophyte infections, including specimen collection, transport, and processing; the microscopic examination and culture of clinical specimens from suspected cases of dermatophytosis; and the conventional (phenotypic) and molecular methods of identification of the causative agents, are discussed in detail. Attention is also given to the clinical presentation, diagnosis, and identification of the causative agents for those superficial infections in which the causative fungi colonize the cornified layers of the epidermis or the suprafollicular portion of the hair (tinea versicolor, tinea nigra, black piedra, and white piedra).
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Dermatophyte hyphae in skin scraping. NaOH mount. Magnification, ×400. doi:10.1128/9781555817381.ch123.f1
Dermatophyte hyphae in skin scraping. NaOH mount. Magnification, ×400. doi:10.1128/9781555817381.ch123.f1
Microsporum audouinii, ectothrix type of hair invasion. Magnification, ×400. doi:10.1128/9781555817381.ch123.f2
Microsporum audouinii, ectothrix type of hair invasion. Magnification, ×400. doi:10.1128/9781555817381.ch123.f2
Trichophyton tonsurans, endothrix type of hair invasion. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f3
Trichophyton tonsurans, endothrix type of hair invasion. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f3
Hair infected by Trichophyton schoenleinii from a patient with favus. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f4
Hair infected by Trichophyton schoenleinii from a patient with favus. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f4
Smooth-walled macroconidia of Trichophyton ajelloi. Magnification, ×400. doi:10.1128/9781555817381.ch123.f5
Smooth-walled macroconidia of Trichophyton ajelloi. Magnification, ×400. doi:10.1128/9781555817381.ch123.f5
Macroconidia and microconidia of Trichophyton mentagrophytes complex on SGA with 5% NaCl. Magnification, ×400. doi:10.1128/9781555817381.ch123.f6
Macroconidia and microconidia of Trichophyton mentagrophytes complex on SGA with 5% NaCl. Magnification, ×400. doi:10.1128/9781555817381.ch123.f6
Smooth-walled macroconidia of Afro-Asiatic type Trichophyton rubrum (T. raubitschekii) from primary isolate on SGA. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f7
Smooth-walled macroconidia of Afro-Asiatic type Trichophyton rubrum (T. raubitschekii) from primary isolate on SGA. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f7
Long, narrow macroconidium and clavate to pyriform microconidia of Trichophyton rubrum. Magnification, ×400. doi:10.1128/9781555817381.ch123.f8
Long, narrow macroconidium and clavate to pyriform microconidia of Trichophyton rubrum. Magnification, ×400. doi:10.1128/9781555817381.ch123.f8
Clavate macroconidium, microconidia, and intermediate conidia of Trichophyton terrestre. Phase contrast; magnification, ×400. doi:10.1128/9781555817381.ch123.f9
Clavate macroconidium, microconidia, and intermediate conidia of Trichophyton terrestre. Phase contrast; magnification, ×400. doi:10.1128/9781555817381.ch123.f9
Microconidia with typical refractile cytoplasm of Trichophyton tonsurans. Magnification, ×400. doi:10.1128/9781555817381.ch123.f10
Microconidia with typical refractile cytoplasm of Trichophyton tonsurans. Magnification, ×400. doi:10.1128/9781555817381.ch123.f10
Characteristic chlamydospores produced by Trichophyton verrucosum or BCP-milk solids-yeast extract agar. Magnification, ×400. doi:10.1128/9781555817381.ch123.f11
Characteristic chlamydospores produced by Trichophyton verrucosum or BCP-milk solids-yeast extract agar. Magnification, ×400. doi:10.1128/9781555817381.ch123.f11
Macroconidia of Epidermophyton floccosum on SGA. Note the absence of microconidia. Magnification, ×400. doi:10.1128/9781555817381.ch123.f12
Macroconidia of Epidermophyton floccosum on SGA. Note the absence of microconidia. Magnification, ×400. doi:10.1128/9781555817381.ch123.f12
Macroconidia of Microsporum audouinii on SGA with 3% NaCl. Magnification, ×400. doi:10.1128/9781555817381.ch123.f13
Macroconidia of Microsporum audouinii on SGA with 3% NaCl. Magnification, ×400. doi:10.1128/9781555817381.ch123.f13
Macroconidia of Microsporum canis with rough, thick walls. Magnification, ×400. doi:10.1128/9781555817381.ch123.f14
Macroconidia of Microsporum canis with rough, thick walls. Magnification, ×400. doi:10.1128/9781555817381.ch123.f14
Macroconidia of Microsporum cookei, showing thick walls and pseudosepta. Magnification, ×400. doi:10.1128/9781555817381.ch123.f15
Macroconidia of Microsporum cookei, showing thick walls and pseudosepta. Magnification, ×400. doi:10.1128/9781555817381.ch123.f15
Macroconidia of Microsporum gypseum. Magnification, ×400. doi:10.1128/9781555817381.ch123.f16
Macroconidia of Microsporum gypseum. Magnification, ×400. doi:10.1128/9781555817381.ch123.f16
Rough-walled macroconidium of Microsporum persicolor on SGA with 3% NaCl. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f17
Rough-walled macroconidium of Microsporum persicolor on SGA with 3% NaCl. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f17
(a) Trichophyton mentagrophytes complex: “nodular” variant of Trichophyton interdigitale (formerly Trichophyton krajdenii), SGA, 12 days, showing typical bright yellow pigmentation. (b) Trichophyton mentagrophytes complex: granular, zoophilic type Trichophyton interdigitale (mating tester strain of Arthroderma vanbreuseghemii), 14 days. (c) Trichophyton rubrum, SGA, 10 days, surface showing cottony white mycelium. (d) Trichophyton rubrum, SGA, 10 days, reverse showing typical red pigment. (e) Trichophyton tonsurans, SGA, 14 days, surface showing low velvety texture, mixed white and brownish mycelium. (f) Trichophyton tonsurans, SGA, 14 days, reverse showing mixture of mahogany red-brown and sulfur yellow coloration. (g) Microsporum canis, SGA, 10 days, relatively flat colony showing pale striate margin and yellowish pigment near colony center. (h) Brown filaments of Hortaea werneckii in NaOH mount of scraping from tinea nigra. Magnification, ×400. doi:10.1128/9781555817381.ch123.f18
(a) Trichophyton mentagrophytes complex: “nodular” variant of Trichophyton interdigitale (formerly Trichophyton krajdenii), SGA, 12 days, showing typical bright yellow pigmentation. (b) Trichophyton mentagrophytes complex: granular, zoophilic type Trichophyton interdigitale (mating tester strain of Arthroderma vanbreuseghemii), 14 days. (c) Trichophyton rubrum, SGA, 10 days, surface showing cottony white mycelium. (d) Trichophyton rubrum, SGA, 10 days, reverse showing typical red pigment. (e) Trichophyton tonsurans, SGA, 14 days, surface showing low velvety texture, mixed white and brownish mycelium. (f) Trichophyton tonsurans, SGA, 14 days, reverse showing mixture of mahogany red-brown and sulfur yellow coloration. (g) Microsporum canis, SGA, 10 days, relatively flat colony showing pale striate margin and yellowish pigment near colony center. (h) Brown filaments of Hortaea werneckii in NaOH mount of scraping from tinea nigra. Magnification, ×400. doi:10.1128/9781555817381.ch123.f18
Malassezia furfur in skin scrapings from a lesion of tinea versicolor (Kane’s stain). Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f19
Malassezia furfur in skin scrapings from a lesion of tinea versicolor (Kane’s stain). Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f19
Culture of Malassezia furfur on Littman oxgall agar overlaid with oil. doi:10.1128/9781555817381.ch123.f20
Culture of Malassezia furfur on Littman oxgall agar overlaid with oil. doi:10.1128/9781555817381.ch123.f20
Microscopic appearance of Malassezia furfur yeast cells on Littman oxgall overlaid with olive oil. Magnification, ×400. doi:10.1128/9781555817381.ch123.f21
Microscopic appearance of Malassezia furfur yeast cells on Littman oxgall overlaid with olive oil. Magnification, ×400. doi:10.1128/9781555817381.ch123.f21
Black piedra nodules on scalp hair. NaOH mount. Magnification, ×100. doi:10.1128/9781555817381.ch123.f22
Black piedra nodules on scalp hair. NaOH mount. Magnification, ×100. doi:10.1128/9781555817381.ch123.f22
White piedra nodule on hair from the groin. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f23
White piedra nodule on hair from the groin. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f23
Arthroconidia from a crushed nodule of white piedra. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f24
Arthroconidia from a crushed nodule of white piedra. Magnification, ×1,000. doi:10.1128/9781555817381.ch123.f24
Important characteristics of clinically isolated dermatophytes and dermatophytoids
Important characteristics of clinically isolated dermatophytes and dermatophytoids
Grouping of dermatophytes on the basis of host preference and natural habitat a
Grouping of dermatophytes on the basis of host preference and natural habitat a
Hair invasion by dermatophytes on the human host
Hair invasion by dermatophytes on the human host
Dermatophyte nutritional response as elucidated by Trichophyton agars a
Dermatophyte nutritional response as elucidated by Trichophyton agars a
Sequence of procedures for phenotypic identification of dermatophytes in pure culture a
Sequence of procedures for phenotypic identification of dermatophytes in pure culture a