Dermatophytes

Dermatophytes

Species and Classification

• Three common genii:
  • Epidermophyton
  • Microsporum
  • Trichophyton
• Three categories: anthropophilic, zoophilic, and geophilic

Presentation

• Clinical presentation is usually ringworm
  • Most active form in the periphery of the ring
  • Can invade immunocompromised patients, e.g. Majocchi's granuloma and kerion
• Named by anatomic location
  • Tinea capitis: head
  • Tinea corporis: body
  • Tinea cruris: groin
  • Tinea unguun: nails

Diagnosis

Specimen collection

• Hair: need the root, with sterile forceps
• Skin: disinfect with alcohol or sterile water, then scrape the border with a blunt scalpel
• Nails: alcohol gauze to clean, then scrape subungual debris

Laboratory Testing

• Direct microscopy: KOH (potassium hydroxide) calcofluor of skin scraping, under UV light
• Culture with Littman agar w streptomycin, Sabouraud agar with chloram+gent, Sabouraud agar with CG+cyclohexamide
  • Incubate for 2-3 weeks at 30ºC

Indentification

• Chemical properties
  • Growth at 37ºC
  • Urease production/urea hydrolysis
  • BCP-MSG reaction (important)
  • Hair perforation test
  • Vitamin requirements with trichophyton agars T1 to T7
  • Growth on polished rice grain
• Colony features
  • Speed of growth
  • Colour on surface
  • Texture
  • Colour on reverse
• Microscopic features
  • Macroconidia, microconidia, septae