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Fungos filamentosos

Fusarium spp.

Hyaline septate hyphae with branching at variable angles

Identification & Growth

Identification

  • Canoe- or banana-shaped macroconidia and microconidia in false heads
  • Cottony colonies with pink, violet or lilac reverse pigment

Growth Conditions

  • Sabouraud without cycloheximide, 25–30 °C, 3–5 days; also grows at 37 °C

Clinical Significance

  • Keratitis in contact lens wearers and onychomycosis in immunocompetent patients
  • Disseminated fusariosis with skin lesions and positive blood cultures in severely neutropenic patients

Intrinsic Resistance

  • High intrinsic resistance to azoles and to the echinocandins

Bench Alerts

  • One of the few filamentous fungi that grow in blood cultures — do not dismiss it as a contaminant
  • Susceptibility by broth microdilution (CLSI M38/EUCAST E.Def 9); no standardised disk method

Clinical Notes

Clinical presentations

  • Fungal keratitis and onychomycosis in immunocompetent hosts, frequently associated with ocular trauma or contact lens use.
  • Disseminated invasive fusariosis, including sinusitis, pneumonia and metastatic skin lesions, in severely and prolongedly neutropenic patients and hematopoietic stem cell transplant recipients.
  • Fungemia documentable by blood culture, a feature that distinguishes Fusarium from other invasive filamentous molds such as Aspergillus.

Specimens and collection

  • Corneal scraping for direct examination and culture in cases of keratitis, processed urgently given the aggressiveness of ocular infection.
  • Routine blood culture, which has good sensitivity for Fusarium fungemia, unlike most other molds.
  • Skin and deep tissue biopsy with histopathology and culture in disseminated disease, correlated with serum galactomannan and beta-D-glucan when available.

Epidemiology and at-risk populations

  • Ubiquitous environmental filamentous fungus in soil and plant material, with species of the F. solani species complex most frequently associated with invasive disease.
  • Profound and prolonged neutropenia is the main risk factor for invasive and disseminated fusariosis.
  • Outbreaks of keratitis linked to contaminated contact lens cleaning solutions have been described, reinforcing the importance of exposure history.

Resistance and therapeutic implications

  • High intrinsic resistance to multiple antifungals, including elevated MICs for azoles (with some exceptions for voriconazole/posaconazole in certain isolates) and for echinocandins.
  • CLSI M38 and EUCAST AFST provide reference methods for MIC determination in filamentous fungi, but formal clinical breakpoints for Fusarium spp. are limited; interpretation generally relies on epidemiological cutoff values (ECV, CLSI M60).
  • Lipid amphotericin B and voriconazole are the first-line options recommended by guidelines, combined with reduction of immunosuppression when feasible.

Bench and reporting notes

  • Rapidly growing, cottony colonies with variable pigmentation (white, pink, violet), producing characteristic multiseptate, canoe-shaped macroconidia.
  • Species-level identification by sequencing (TEF-1α region) is recommended given the impact on susceptibility and prognosis across species complexes.
  • Promptly notify the clinician of isolation from blood culture or deep material in a neutropenic patient, given the aggressiveness and need for early therapy.

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 Fusarium spp. in the lab?

Fusarium spp. is identified through canoe- or banana-shaped macroconidia and microconidia in false heads, cottony colonies with pink, violet or lilac reverse pigment.

What are the intrinsic resistances of Fusarium spp.?

This organism is naturally resistant to high intrinsic resistance to azoles and to the echinocandins. These drugs should not be reported as susceptible.

Where is Fusarium spp. commonly found?

It is typically associated with keratitis in contact lens wearers and onychomycosis in immunocompetent patients, disseminated fusariosis with skin lesions and positive blood cultures in severely neutropenic patients.

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