Dematiaceous Molds

• Molds normally considered environmental contaminants:

  • Zygomycetes (Phycomycetes) are sparsely septate and hyaline, including Lichtheimia (Absidia), Mucor, Rhizopus, Syncephalastrum, Cunninghamella
  • Hyaline molds are septate with transparent hyphae, such as Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, Penicillium, Fusarium, Acremonium, Chrysosporium, Sepedonium
  • Dematiaceous fungi have septate, dark-colored hyphae, like Alternaria, Cladosporium, Aureobasidium, Curvularia, Epicoccum, Drechslera, Nigrospora, Ulocladium, Bipolaris
• Dematiaceous molds can cause Phaeohyphomycosis, which is a condition of fungi with dark hyphae, leading to superficial skin infections, keratitis, cyst formation, allergic sinusitis, and disseminated infections

  • Over 100 fungal isolates have been identified causing human infections
  • Dematiaceous fungi can produce melanin within cell walls and form yeast and/or hyphal elements in host tissues
• • Risk factors include neutropenia, solid-organ transplant, bone-marrow transplant, chronic corticosteroid use, and skin or soft tissue trauma
• Characteristics of Dematiaceous molds and Phaeohyphomycosis:

  • Ubiquitous saprobes found in soil, decaying matter, and as plant pathogens
  • Infections can occur worldwide, with specific locations like feet and hands in the tropics, and allergic sinusitis in the southern US
  • Histopathology shows hyphal invasion in sterile tissues
  • Melanin is a virulence factor, providing resistance to neutrophil reactive oxygen species
  • Chitin may also be a virulence factor, as chitin mutants are less able to cause host infections
• Phaeohyphomycosis Case Study #1:

  • A 46-year-old male, 2 weeks post ABO-incompatible renal transplantation, developed cerebral involvement with depression, seizure, and left-side hemiparesis
  • The pathogen causing infection was Cladophialophora (Cladosporium) carrionii
  • Treatment included broad-spectrum antimicrobials, stopping immunosuppressants, and using amphotericin B
  • The patient grew olive to black colonies in approximately 14 days
• Phaeohyphomycosis Case Study #2:

  • A 32-year-old female with disseminated Phaeohyphomycosis, no known immunosuppression, and a 12-year history of relapsing infection
  • The pathogen causing infection was Exophiala sp. (spinifera)
  • Treatment involved emergency cesarean section for premature delivery and the use of Posaconazole
  • Disseminated disease can lead to mortality, with surgery and over 24 months of treatment required
• Phaeohyphomycosis Case Study #3:

  • A 56-year-old male with papular nodules and dermal papillae on the left foot, with a 10-year history without incidences
  • The pathogen causing infection was Bipolaris sp. (spicifera)
  • Treatment included itraconazole and terbinafine for 3 months, resulting in clearance of the infection
• Phaeohyphomycosis Case Study #4:

  • A 21-year-old male with allergic bronchopulmonary mycosis, presenting with worsening asthma, fever, and night sweats
  • The pathogen causing infection was Alternaria sp.
  • Treatment involved Amoxicillin, clarithromycin, inhaled steroid treatment, and later itraconazole
  • No standard treatment algorithm exists, with options like Amphotericin B, 5-FC, fluconazole, itraconazole, and terbinafine
• Other Saprophytic Dematiaceous Molds - Common Contaminants:

  • Curvularia sp. can cause infections in both humans and animals, with rapid growth and woolly colonies
  • Epicoccum sp. is widely distributed but does not commonly infect humans or animals, with moderate growth and yellow to red colonies
  • Nigrospora sp. is widely distributed in soil and seeds, rarely causing infections, with rapid growth and black colonies
  • Fonsecaea sp. is associated with invasive infections in immunocompromised individuals, with slow growth and olivaceous to brown-black colonies
• Key identifying characteristics of different Dematiaceous molds:

  • Fonsecaea type produces velvety colonies with oval, single-celled conidia
  • Cladosporium type produces shield-shaped conidia in short branching chains
  • Phialophora type has phialides with terminal cup-shaped collarettes
  • Rhinocladiella type bears oval conidia at the tip and on the side of the conidiophore