Topic 8 - BIOLOGY AND DISEASES CAUSED BY SELECTED DERMATOPHYTES

DERMATOPHYTES

• Filamentous fungi, commonly called molds

• Cause infections of keratinized tissues

skin, hair, nails

Dermatophytes primarily affect

dermatophytoses

Infections of dermatophytes are called

keratinized material

Dermatophytes obtain nutrients from —, allowing them to colonize these areas

ringworm

Dermatophytoses or dermatomycoses are commonly called as —

Anthropophilic, zoophilic, geophilic (soil)

Three major reservoirs of dermatophytoses

• Direct contact with infected people or animals

• Contaminated surfaces and objects

Transmission of dermatophytoses may occur through:

Tinea pedis, tinea corporis, tinea capitis, tinea cruris, tinea barbae, tinea unguium

Common Tinea infections

tinea pedis

tinea infection of the feet

tinea corporis

tinea infection of the body

tinea capitis

tinea infection of the scalp and hair

tinea cruris

tinea infection of the groin

tinea barbae

tinea infection of the beard

tinea unguium

tinea infection of the nails

Epidermophyton, Microsporum, Trichophyton

Three major dermatophyte genera

skin and nails

Epidermophyton primarily infects

Skin and hair

Microsporum primarily infects

skin, hair, and nails

Trichophyton primarily infects

specimens, direct examination, culture, identification

how are dermatophytes identified

skin scrapings, hair, nail clippings

how are dermatophytes identified (specimen)

KOH Preparation, Detects fungal hyphae

how are dermatophytes identified (Direct examination)

Saboraud dextrose agar

how are dermatophytes identified (Culture)

Colony morphology, microscopic morphology, conidia and hyphae

how are dermatophytes identified (Identification)

• Common causes of skin, hair, and nail infections

• Cause multiple forms of tinea infection

• Adapted to utilize keratin

• Can spread through people, animals, soil, and contaminated objects

• Identification relies on clinical, macroscopic, and microscopic characteristics

Medical importance of dermatophytes

Epidermophyton floccosum

Medically important species of Epidermophyton

Anthropophilic

Epidermophyton is — primarily associated with humans

EPIDERMOPHYTON

• Keratinophilic filamentous fungus

• Primarily infects skin and nails

• Not known to invade hair in vivo

• Widely distributed, including tropical and subtropical regions

• Greenish-brown to khaki

• Suede-like surface

• Center becomes raised and folded

• Peripheral region remains flatter

• White mycelial tufts may develop with age

• Reverse: yellowish-brown to brown

Macroscopic appearance of Epidermophyton

Smooth, Thin-walled, Club-shaped, occur singly or in clusters. May occur in groups of 2–3

Microscopic appearance of Epidermophyton (Macroconidia)

Thick-walled, round to oval structures, develop from hyphal cells, more common in older cultures

Microscopic appearance of Epidermophyton (Chlamydospores)

Tinea cruris—groin, Tinea pedis—feet, Tinea corporis—body, Tinea unguium—nails

Major infections of Epidermophyton

Scaling, Erythema, Hyperpigmentation, Pruritus/itching, Lesions may be annular, Tinea cruris may be bilateral

Common clinical features of Epidermophtyon

Tinea cruris and tinea pedis

are particularly important manifestations of E. floccosum.

MICROSPORUM

• Genus of dermatophytic fungi that infect keratinized tissues

• Primarily skin and hair, less commonly in nails

Anthropophilic – associated with humans, Zoophilic – associated with animals, Geophilic – associated with soil

Ecological groups of microsporum

Microspirum audouinii, Micropsorum canis, Microporum ferrugineum

Current genus includes 3 recognized species:

Lophophyton, Nannizzia, and Paraphyton

Former Microsporum species have been reassigned to

Microsporum audouinii

• what microsporum species is an anthropophilic dermatophyte primarily infecting humans

• Particularly common in children

• Produces relatively non-inflammatory infections

scalp and skin

M. audouinii mainly affects

ectothrix

M. audouinii causes hair infection through an — pattern

bright greenish-yellow fluorescence ; Woods light

Infected hairs of M. audouinii typically show — under — light

Flat and spreading; good growth on vitamin-free agar (Trichophyton agar No. 1); very poor or absent growth on rice grains

Colony growth of Microsporum audouinii

Greyish-white to light tan-white

Surface color of M. audouinii

Dense, suede-like to downy, resembling mouse fur

Texture of M. audouinii

Flat, spreading colonies; conidia are rarely produced, with most cultures sterile; occasional thick-walled terminal or intercalary chlamydospores may occur

Central Features of M audouinii

Yellow-brown to reddish-brown; some strains may show no reverse pigment

Reverse pigmentation of M audouinii

Salmon to pinkish-brown reverse pigmentation

Growth of M audouinii on Potato dextrose agar (PDA):

Profuse growth; rapid alkaline pH change produces a purple color

Growth of M. audouinii on BCP milk solids glucose agar

• Rarely produced or absent in most cultures

• Single-celled, hyaline, smooth-walled

• Pyriform to clavate in shape

Microconidia of M. audouinii

• Rarely produced or absent in most cultures

• When present, resemble those of M. canis

• Longer, smoother, and more irregularly fusiform

• Multicellular and multiseptate

Macroconidia of M. audouinii

• Occasional thick-walled chlamydospores

• Chlamydospores may be terminal or intercalary

• Pectinate (comb-like) hyphae may be present

• Racquet hyphae may be present

Other Structures of M. audouinii

Negative after 28 days

what is he hair perforation test for M audouinii

Microsporum ferrugineum

• Anthropophilic dermatophyte primarily associated with human infection

• Important cause of tinea capitis, particularly in children

• Associated with epidemic outbreaks of tinea capitis

• Hair infection occurs through an ectothrix pattern

• Infected hairs may show greenish-yellow fluorescence under Wood’s light

Slow-growing; cultures rapidly become downy and pleomorphic

Colony growth of M. ferrugineum

Cream to buff; may vary from cream to yellow to deep red; a flatter white form may also occur

Surface color of M. ferrugineum

Initially waxy and glabrous; later becomes downy

Texture of M. ferrugineum

Convoluted thallus; pleomorphic with age

Central Features of M. ferrugineum

No reverse pigment

pigmentation of M. ferrugineum

Bamboo hyphae

are a distinctive feature of the species of M. ferurugineum