Dermatophytosis and Superficial Mycoses

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Dermatophytosis and Superficial Mycoses

• Microsporum
• Trichophyton
• Epidermophyton
• Malassezia furfur
• P. werneckii
• Piedraia hortae
• Trichosporon beigelii

Dermatophytes
Superficial Mycoses
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Mycoses of Skin, Hair, and Nails

• Mycoses of skin, hair, and nails are grouped
  according to which layers are affected and
  clinical manifestations
• Superficial mycoses are fungal infections of the
  outermost keratinized (cornfield?) layers of the
  skin or hair shaft resulting in essentially no
  pathological changes. No cellular immune
  response in elicited minimal humoral host
  response - IgA
• These mycoses are largely cosmetic involving skin
  pigmentation or forming nodules along distal hair
  shafts often asymptomatic host is unaware

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Mycoses of Skin, Hair, and Nails

• The superficial mycoses are
• Malassezia furfur ? tinea versicolor (seborrhea?,
  dandruff?)
• Phaeoannelomyces werneckii ? tinea nigra
• Piedraia hortae ? black piedra
• Trichosporon beigelii ? white piedra
• Dermatophytosis involve deeper layers of skin,
  hair, and nails with varied clinical
  manifestations and are caused by species of the
  fungal genera Trichophyton, Epidermophyton, and
  Microsporum (in order of commonality).
• Your text classifies these under superficial
• Other sources classify them under cutaneous (U.
  of Adelaide)

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Dermatophytes

• Dermatophytes are keratinophilic fungi they
  possess keratinase allowing them to utilize
  keratin as a nutrient energy source
• They infect the keratinized (horny) outer layer
  of the scalp, glabrous skin, and nails causing
  tinea or ringworm
• Although no living tissue is invaded (keratinized
  stratum only colonized) the infection induces an
  allergic and inflammatory eczematous response in
  the host
• Lesions on skin and sometimes nails have a
  characteristic circular pattern that was mistaken
  by ancient physicians as being a worm down in the
  tissue
• These lesions are still today called ringworm
  infections even though the etiology is known to
  be a fungus rather than a worm

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Classical Ringworm Lesion
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Dermatophytes

• Taxonomic classification
• They belong to the phylum Deuteromycota (Fungi
  Imperfecti)
• They are hyaline moulds (transparent / white)
• Three genera comprise this group
• Microspourm
• Trichophyton
• Epidermophyton

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Dermatophytes

• Classification
• There are many species of dermatophytes but only
  a few are commonly encountered in developed
  countries
• Identifying the dermatophytes to the species
  level is not usually required because
  antimicrobial therapy is the same for all isolates

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Dermatophytes

• Direct Examination
• Treating skin and nail scrapings and snippets
  of hair with potassium hydroxide (KOH dissolves
  keratin but not chitin - hyphae) is usually very
  effective in detecting dermatophyte hyphae in
  clinical specimens.
• The addition of calcofluor white (1,4 polymer
  specific fluorochrome dye) and dimethylsulfoxide
  (DMSO) to the KOH and viewing with a fluorescent
  microscope is recommended. DMSO is a non-polar
  surfactant (wetting agent) which aids in clearing
  of the keratin by making KOH more soluble in the
  sample.

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Dermatophytes

• Direct Examination
• The pattern of growth in the infected hair taken
  directly from the patient is characteristic of
  some dermatophytic fungi
• Some grow only inside the hair shaft (endothrix)
• Some grow inside and outside the hair shaft
  (ectothrix)