CHAPTER 60

• Septate dematiaceous molds considered in superficial infections:

  • Cyphellophora spp.
  • Hortaea werneckii
  • Piedraia hortae
  • Knufia epidermidis
  • Phialophora europaea
  • Neoscytalidium dimadiatum (Previously Scytalidium dimidiatum)
• General characteristics of dematiaceous molds:

  • Characterized by dark colorization
  • Has the ability to produce melanin
  • Known agents of superficial and subcutaneous mycoses
  • Less commonly cause deeply invasive or disseminated disease
  • Ubiquitous in nature
  • Serve as saprophytes and plant pathogens
  • Humans and animals can serve as accidental hosts after traumatic inoculation of the organisms into cutaneous and subcutaneous tissues
• Growth rate of dematiaceous molds:

  • Slow-growing dematiaceous molds require 7 to 10 days to grow
  • Rapid-growing dematiaceous molds usually grow in less than 7 days
• Common etiologic agents caused by dematiaceous fungi:

  • Mycetoma
  • Chromoblastomycosis
  • Phaeohyphomycosis
• Epidemiology and pathogenesis of superficial infections:

  • Tinea nigra: caused by Hortaea werneckii, manifested by blackish brown macular patches on the skin
  • Black piedra: fungal infection of the hair caused by Piedraia hortae
  • Hyperkeratosis: caused by Neoscytalidium dimidiatum, leading to thickening of the epidermis
• Mycetoma is a chronic granulomatous infection characterized by swelling, purplish discoloration, tumorlike deformities of subcutaneous tissue, and sinus tracts that drain purulent material containing granules
• Chromoblastomycosis is a chronic fungal infection characterized by the development of papules that enlarge to form warty or tumorlike lesions
• Phaeohyphomycosis is a general term for infections caused by dematiaceous organisms, including molds, brownish yeastlike cells, pseudohyphae, and hyphae, leading to various symptoms and diseases
• Laboratory diagnosis methods for dematiaceous molds:

  • Direct detection method using stains like Fontana-Masson stain and silver nitrate
  • Serologic testing is not useful for diagnosis
  • Molecular methods like nucleic acid amplification assays and nucleic acid-based sequencing of ribosomal genes can be used for identification
• Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is successfully used to identify clinically relevant fungal isolates
• Cultivation of dematiaceous molds:

  • Hortaea werneckii (causative agent of tinea nigra) grows very slowly
• H. werneckii, the causative agent of tinea nigra:

  • Grows very slowly
  • Initial colonies are olive to black, yeastlike, and shiny
  • As the culture ages, it becomes filamentous with velvety gray aerial hyphae
  • Grows within 2 to 3 weeks
• P. hortae, the causative agent of black piedra:

  • Easily cultured on any fungal culture medium lacking cycloheximide
  • Slow-growing, appearing dark brown to black, and producing aerial mycelium
• Cyphellophora:

  • Produces slender, curved, one- to three-septate conidia
  • Conidia are produced on collarettes
• Exophiala:

  • A black yeast that demonstrates a high degree of morphologic variability
  • Conidia are produced from narrow scars or extensions referred to as annelidic
  • Capable of growth at 40°C
  • Fails to assimilate nitrate
• Phialophora:

  • Produces phialides (flask-shaped)
  • No budding cells
• Neoscytalidium dimidiatum:

  • Rapidly growing black arthroconidia in culture
• Mycetoma - White Grain Mycetoma caused by P. boydii:

  • Grows rapidly (5-10 days) on common laboratory media
  • Initial growth is white and fluffy, aging to brownish gray
  • The reverse side of the colony progresses from tan to dark brown
• Acremonium spp. (Acremonium falciforme):

  • Grow slowly and produce gray to brown colonies
• Black Grain Mycetoma:

  • Includes Exophiala jeanselmei, Curvularia spp., and Madurella spp.
  • Slow-growing and vary from white to olive-brown
• T. grisea:

  • Slow-growing with velvety colonies
  • Appear smooth or radially furrowed and dark gray or olive brown to black
  • The reverse side appears black
  • Hyphae are septate and non-sporulating
• Chromoblastomycosis:

  • Includes Cladophialophora:
  • Dematiaceous and slow-growing
  • Produce heaped-up, slightly folded, darkly pigmented colonies
  • Gray to olive to black with a suedelike appearance
  • The reverse side is jet black
• Approach to Identification:

  • Superficial Infections:
  • H. werneckii produces yeast-like cells that may be one- or two-celled
  • P. hortae usually does not sporulate but demonstrates highly septate, dematiaceous hyphae and swollen intercalary cells
• Antifungal Susceptibilities:

  • Effective with melanized fungi:
  • Amphotericin B
  • Azoles
• Broad spectrum of activity:

  • Triazoles
  • Posaconazole
  • Voriconazole
• Voriconazole associates with the occasional treatment failure of mycetoma