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Fungos filamentosos

Mucorales (Rhizopus, Mucor, Lichtheimia)

Broad, hyaline, coenocytic (sparsely septate) hyphae branching at right angles

Identification & Growth

Identification

  • Sporangiophores with sporangium and columella; rhizoids define the genus
  • 'Cotton candy' colonies filling the plate in 24–72 h

Growth Conditions

  • Sabouraud without cycloheximide, 30–37 °C; explosive growth in 1–3 days

Clinical Significance

  • Rhino-orbito-cerebral mucormycosis in uncontrolled diabetes and ketoacidosis
  • Pulmonary and cutaneous forms in neutropenic and severely burned patients

Intrinsic Resistance

  • Intrinsic resistance to voriconazole, fluconazole, echinocandins and 5-flucytosine

Bench Alerts

  • Medical emergency: communicate the finding immediately, before the final report
  • Do not grind the specimen — homogenisation destroys the coenocytic hyphae and the culture turns negative

Clinical Notes

Clinical presentations

  • Rapidly progressive rhino-orbito-cerebral mucormycosis, most frequent in patients with diabetic ketoacidosis or poorly controlled diabetes.
  • Angioinvasive pulmonary mucormycosis in neutropenic patients and transplant recipients, with potential for hematogenous dissemination.
  • Cutaneous and soft-tissue mucormycosis after penetrating trauma, burns or contaminated dressings, including aggressive necrotizing forms.

Specimens and collection

  • Tissue biopsy with histopathology (broad, non-septate to pauci-septate hyphae with right-angle branching) is essential, as angioinvasion can limit blood culture yield.
  • Fresh tissue culture without aggressive maceration, since excessive fragmentation of hyphae reduces fungal viability in culture.
  • Pan-fungal or Mucorales-specific PCR on tissue or plasma can complement diagnosis when culture is negative, particularly after antifungal therapy has begun.

Epidemiology and at-risk populations

  • Order of ubiquitous environmental fungi (Rhizopus, Mucor, Lichtheimia, among other genera) found in soil, decaying organic matter and dust.
  • Diabetic ketoacidosis, prolonged neutropenia, corticosteroid use, iron overload and deferoxamine use are well-established risk factors.
  • Increased incidence reported following COVID-19 waves, associated with corticosteroid therapy and uncontrolled diabetes (COVID-19-associated mucormycosis).

Resistance and therapeutic implications

  • Intrinsic resistance to voriconazole and to echinocandins used alone; high-dose lipid amphotericin B is the mainstay of systemic antifungal treatment.
  • Isavuconazole and posaconazole show variable in vitro activity and are used as maintenance or salvage therapy per ECMM/ESCMID/MSGERC guidelines.
  • MIC testing by CLSI M38/EUCAST AFST is available, but clinical breakpoints are not standardized for Mucorales; in vitro-in vivo correlation remains uncertain, and early surgical debridement is decisive for outcome.

Bench and reporting notes

  • Broad hyphae (6–25 µm), non-septate to pauci-septate, with right-angle (~90°) branching, distinct from the septate, acute-angle branching hyphae of Aspergillus.
  • Genus and species identification by sporangial/sporangiospore morphology and confirmation by molecular sequencing when available, given the prognostic and therapeutic impact across genera.
  • Urgent communication to the clinician upon histopathologic suspicion or positive culture, as mucormycosis is a medical-surgical emergency with high mortality if treatment is delayed.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Mucorales (Rhizopus, Mucor, Lichtheimia) in the lab?

Mucorales (Rhizopus, Mucor, Lichtheimia) is identified through sporangiophores with sporangium and columella; rhizoids define the genus, 'cotton candy' colonies filling the plate in 24–72 h.

What are the intrinsic resistances of Mucorales (Rhizopus, Mucor, Lichtheimia)?

This organism is naturally resistant to intrinsic resistance to voriconazole, fluconazole, echinocandins and 5-flucytosine. These drugs should not be reported as susceptible.

Where is Mucorales (Rhizopus, Mucor, Lichtheimia) commonly found?

It is typically associated with rhino-orbito-cerebral mucormycosis in uncontrolled diabetes and ketoacidosis, pulmonary and cutaneous forms in neutropenic and severely burned patients.

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