MICROBIOLOGY

• Dermatophytes: filamentous fungi that colonize and digest keratinized structures such as the stratum corneum of skin, hair and nails.
  
  • Cause of superficial infections at those sites with local inflammation and damage.
  • Deeper invasions of the dermis and subcutaneous tissues are rare.
• Dozens of species. T. rubrum is the most commonly isolated organism, but microbiology of infection varies by geographic locale and exposure history.
  • Trichophyton (e.g. T. rubrum, T. interdigitale, T. mentagrophytes, T. tonsurans, T. verrucosum)
  • Microsporum (e.g. M. canis, M. persicolor)
  • Epidermophyton (E. floccosum).
  • Other species: Arthroderma, Ctenomyces, Guarromyces, Lophophyton, Nannizzia, Paraphyton.
• Certain species have a tendency for infection of specific structures:
  • Trichophyton--hair nails and skin
  • Microsporum--hair and skin
  • Epidermophyton--skin and nails.
• Dermatophytes can also be classified according to usual habitat: anthropophilic (humans, e.g. T. rubrum, T. tonsurans, E. floccosum), zoophilic (cats, dogs, e.g. M. canis, T. verrucosum and M. persicolor), geophilic (soil, e.g. M. gypseum).
• Acquisition of dermatophyte spores: can be via direct contact with a human or animal carrier, or indirectly from contaminated surfaces, including household items such as clothing, towels, bedding and combs
• Terbinafine resistance in T. rubrum and T. interdigitale with associated clinical failure is an emerging problem in multiple countries, most notably in India.
• Diagnostics (see more below)
  • Conventional methods such as culture, morphology, growth requirements, biochemical testing and direct microscopy are the mainstay of microbiological identification
  • Advanced methods: nucleic acid amplification (e.g. PCR), MALDI-TOF-MS,