Zygomycetes is a topic covered in the Johns Hopkins Antibiotic (ABX) Guide.

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MICROBIOLOGY

  • The nomenclature is currently in flux.
    • Organisms previously classified as Zygomycetes include those in the subphylum Mucormycotina, which cause the infections classically referred to as mucormycosis.
    • Basidiobolus ranarum and Conidiobolus species, which typically cause subcutaneous infections in tropical regions, were also previously classified as Zygomycetes prior to the change in nomenclature. They now belong to the sub-phylum Entomophthoromycotina.
  • Important causes of mucormycosis: Rhizopus species, Rhizomucor pusillus, Cunninghamella bertholletiae, Apophysomyces elegans, Saksenaea vasiformis, Lichtheimia (Absidia) species, Mucor circinelloides.
    • Most infections are caused by Rhizopus species, but species distribution varies by geographic locale.
  • Micro considerations:
    • Agents of mucormycosis frequently fail to grow in culture.
      • Sensitivity can be improved by placing tissue sections directly on the culture plate without first grinding or homogenizing the material prior to inoculation.
      • Mincing of tissue during specimen preparation can disrupt fungal structure, impairing diagnosis.
    • Appearance in tissue and culture:
      • In tissue: agents of mucormycosis grow in tissue as hyphae with variable width (from 6-25µm), zero or sparse septations, irregular ribbon-like appearance, non-pigmented and wide angle bifurcations including 90 degree angles.
        • Visualization with direct microscopy of tissue samples is facilitated by blankaphor and calcaflour white which bind to the fungal chitin and fluoresce in UV light.
        • The organisms may be seen in histopathology specimens using H+E stains, but visualization is improved with GMS and PAS.
    • In culture:
      • Growth, when it occurs, is usually within 3-5 days on typical fungal culture media (e.g. Sabouraud or potato dextrose agar).
      • Appearance differs by species. Characteristics such as arrangement of spores, and presence, absence, or configuration of specific structures allow for identification of the specific organisms.

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Last updated: September 25, 2016