APIM223887221 - CME/CMLE - Dermatophytes-APIM223887221

APIM223887221 - Educational Activity

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This educational commentary focuses on the identification and morphology of dermatophytes, which are part of the Arthrodermataceae family and include the genera Microsporum, Epidermophyton, and Trichophyton. About 40 species of dermatophytes cause superficial infections of the skin, nails, and hair, requiring keratin to grow. These infections, referred to as tinea, include common conditions like ringworm, athlete’s foot, and jock itch, and are highly contagious through direct contact or fomites.<br /><br />Patients with dermatophyte infections usually exhibit itching, burning, red, scaly, or cracked skin, and possibly hair loss. Differentiation from eczema or psoriasis is needed, often employing potassium hydroxide (KOH) with calcofluor stain or a Wood’s lamp. Definitive diagnosis is achieved through culturing specimens such as hair, skin, or nail clippings on particular growth media.<br /><br />Specimens should be collected aseptically, transported in sterile containers, and processed promptly to ensure accurate culture results. Commonly used agars for dermatophyte cultures include Sabouraud dextrose agar (SDA), Mycosel agar, Inhibitory mold agar (IMA), Potato dextrose agar (PDA), Cornmeal glucose agar, and Dermatophyte test agar. <br /><br />Morphologically, Microsporum species have thick-walled, rough macroconidia and infect skin and hair but rarely nails. Epidermophyton species, characterized by smooth-walled macroconidia and no microconidia, infect skin and nails but not hair. Trichophyton species present thin-walled, smooth macroconidia and numerous microconidia, commonly causing infections in hair, skin, and nails.<br /><br />Correct identification relies on growth rate, colony morphology, microscopic characteristics, and occasionally clinical presentation. Dermatophyte cultures may take up to 21 days to confirm the absence of the organism. The most common dermatophyte in the US is Trichophyton rubrum. Proper isolation and identification are essential for accurate diagnosis and effective treatment of these common skin infections.

Keywords

dermatophytes

Arthrodermataceae

Microsporum

Epidermophyton

Trichophyton

tinea

culturing

Sabouraud dextrose agar

macroconidia

Trichophyton rubrum