Dematiaceous molds

• Phenotypic grouping of fungi based on the presence of melanin

Background

• Melanin is a virulence factor which protects again proteolytic enzymes, oxydation, and phagocytosis
• Includes so-called "black yeast", which appear yeast-like early in culture
• Colonies may grow slowly or quickly (e.g. within a week)
• Pigment may take time to develop, but most will become olive, brown, or black

Microscopy

• Genus identification is made based on a number of microscopic features
  • Annelides are rings that appear following release of conidia at the apex
  • Phialides are cylindrical or flask-shaped cells from which conidia are formed
  • Geniculate pattern is a zig-zag caused by bending at the point of connection for each conidiophore
  • Blastoconidia
  • Arthroconidia
  • Chlamydoconidia
  • Large conidia
    • Single large muriform conifia suggests Epicoccum speices, Alternaria species, and Ulocladium species
    • Single large conidia with transverse septum, suggests Curvularia species or Exserohilum species
  • Small conidia
    • Geniculate conidiophores suggests Fonsecaea species
    • Conidia in chains suggests Cladosporium species or Cladophialophora species
    • Conidia on denticles (stems) suggests Madurella species or Neoscytalidium species
    • Conidia by phialides suggests Phaeoacremonium
  • Unique reproductive bodies
    • Perithecia covered with hairs suggests Chaetomium species
    • Pycnidia with ostioles (holes) suggests Phoma species
• Special tests, including thermal tolerance and germ tube test, can help to distinguish species within a genus
• However, species identification is difficult without molecular assays

Clinical Presentations

• Phaeohyphomycosis typically refers to cutaneous, subcutaneous, and disseminated disease, and is often acquired by traumatic innoculation
  • Superficial cutaneous infection
  • Subcutaneous phaeohyphomycosis
  • Disseminated disease, more common in immunocompromised patients
• Chromoblastomycosis
• Mycetoma

Disease	Organisms	Notes
Localized cutaneous infection or abscess	Alternaria species, Exophiala species, Phialophora species	Traumatic inoculation. Can become disseminated if immunocompromised.
Mycetoma	Madurella species, Exophiala jeanselmei, Leptosphaeria species	Spectrum from cutaneous to deep bone. Chronic draining, including granules.
Chromoblastomycosis	Cladophialophora carrionii, Fonsecaea species, Phialophora species	Chronic subcutaneous infection with sclerotic or muriform bodies
Keratitis		Most common in India. Usually from traumatic inoculation
Black piedra	Piedraia hortae	Present in the tropics. Involves only the hair.
Allergic sinusitis	Bipolaris species, Curvularia species, Exserohilum species	More common in an atopic or asthmatic patient.
Allergic bronchopulmonary disease	Bipolaris species, Curvularia species	Rare.
Pulmonary disease	Scedosporium prolificans, Cladophialophora bantiana	Mostly in immunocompromised patients.
Cerebral disease	Cladophialophora bantiana, Verruonis gallopava, Exserohilum rostratum, Rhinocladiella species, Exophiala dermatitidis	Occurs in immunocompetent people. Species involved varies geographically.
Disseminated disease	Curvularia species, Exophiala species, Bipolaris species, Alternaria species, Verruconis species	Mostly in immunocompromised patients.