Shmuel Shoham, M.D.


  • General description:
    • A darkly pigmented (dematiaceous) filamentous fungus that lives in soil and grasses, especially with warm and humid conditions.
    • E. rostratum is by far the most common infecting species.
      • E. longirostratum and E. mcginnisii have also been reported, but these may actually be the same organism as E. rostratum.
  • Appearance:
    • Under direct microscopy with KOH, Exserohilum spp. appear as brown septate hyphae.
  • Culture:
    • In selective culture media, Exserohilum spp. tend to grow fast.
    • Conidia may take up to 3 weeks to grow.
    • Colonies of Exserohilum spp. have a dark (brown-black or “olivaceous”) color.
    • Appearance of conidia:
      • E. rostratum: long (25-90 by 9-22 μm), straight or slightly curved with 4 to 9 internal septations [Fig 1].
        • Dark bands at both ends and one prominent septum at the base.
        • Color is brown to olivaceous.
        • Protruding hilum that looks like the beak of a bird at the site where the conidia attach at a sharp angle to the conidiophore (conidia bearing filament).
      • E. longirostratum: similar in appearance to E. rostratum, but with larger conidia (up to 228 by 12-19 μm).
      • E. mcginnisii: 44 to 76 by 11 to 18 μm, with 4 to 8 internal septations, warty projections on their outer walls and without dark bands at the ends
  • Non-culture-based diagnostics:
    • Polymerase chain reaction (PCR) has facilitated the process of prompt identification of Exserohilum, but is extremely susceptible to contamination.
      • Results should be used only in conjunction with clinical and epidemiological data.
    • CSF (1-3)-β-D-glucan (BDG) level measurements in outbreak-associated E. rostratum CNS infections:
      • Cutoff of 138 pg/mL provided 100% sensitivity and 98% specificity for the diagnosis of fungal meningitis.
      • The decline in CSF BDG correlated with clinical improvement.
  • Biopsies from tissue invasive disease with Exserohilum spp. will show broad septate hyphae with acute angle branching [Fig 2]. These organisms can be angioinvasive and hyphal elements can be seen in and around blood vessels.

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Last updated: August 29, 2021