Dematiaceous molds

From IDWiki
  • 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
    • Small conidia
    • Unique reproductive bodies
      • Perithecia covered with hairs suggests Chaetomium
      • Pycnidia with ostioles (holes) suggests Phoma
  • 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 Manifestationss

  • 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, Exophiala, Phialophora Traumatic inoculation. Can become disseminated if immunocompromised.
Mycetoma Madurella, Exophiala jeanselmei, Leptosphaeria Spectrum from cutaneous to deep bone. Chronic draining, including granules.
Chromoblastomycosis Cladophialophora carrionii, Fonsecaea, Phialophora 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, Curvularia, Exserohilum More common in an atopic or asthmatic patient.
Allergic bronchopulmonary disease Bipolaris, Curvularia Rare.
Pulmonary disease Scedosporium prolificans, Cladophialophora bantiana Mostly in immunocompromised patients.
Cerebral disease Cladophialophora bantiana, Verruonis gallopava, Exserohilum rostratum, Rhinocladiella, Exophiala dermatitidis Occurs in immunocompetent people. Species involved varies geographically.
Disseminated disease Curvularia, Exophiala, Bipolaris, Alternaria, Verruconis Mostly in immunocompromised patients.

Further Reading

  • ESCMID and ECMM joint clinical guidelines for the diagnosis and management of systemic phaeohyphomycosis: diseases caused by black fungi. Clin Micro Infection. 2014 20(Suppl. 3):47-75. doi: 10.1111/1469-0691.12515