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Culture, Fungus

Test codes: , 4553, 4605, 39515, 39522

A sterile hyphae result indicates the absence of asexually produced spores (conidia). Lack of conidia complicates classification of a mold. Thus, a report of sterile hyphae is consistent with presence of either a dermatophyte or a contaminant (some nondermatophytes can infect nails).

If hyphae were not seen on direct examination of tissue, hair, or nails, then a contaminant is more likely. A report of sterile hyphae excludes Coccidioides immitis/posadasii because arthroconidia are expressed in their mature cultures. Molecular testing could be considered for sterile hyphae encountered from culture of specimens from normally sterile sites such as blood or tissue.

Zygomycetes produce fragile, haphazardly branching hyphae in tissue, and these are easily disrupted during biopsy and specimen processing, producing sterile cultures. More than half of zygomycetes tissue cultures produce no growth.1

To improve chances of growth, submit larger biopsies rather than smaller biopsies, and limit refrigeration during transport if at all possible.

Dermatophytes are molds that can digest keratin from hair, skin, or nails. Living tissue is generally not involved and the host reaction to fungal products produces clinical symptoms. Major genera of dermatophytes are Microsporum, Trichophyton, and Epidermophyton.² Other yeasts and molds infect skin and nails in addition to dermatophytes.

No. Candida albicans is normally found in stool; thus, a stool culture for Candida has no medical significance. Stool cultures for fungus should not be performed.2 Fungal enteritis is rare and usually is only encountered in patients with severe systemic disease.

A patient may ask for this test because popular belief holds that systemic candidiasis is a cause of chronic fatigue, but this is not supported by medical evidence.

The following fungi are considered emerging pathogens:

  • Aspergillus terreus is the only Aspergillus species that can readily produce positive blood cultures owing to its ability to produce conidia within tissues. Aspergillus terreus is resistant to amphotericin B.
  • Candida auris can cause bloodstream, wound, and ear infections. C auris is known to have mutations that confer multi-drug antifungal resistance.3
  • Cryptococcus gattii produces disease identical to that of Cryptococcus neoformans but may infect patients without obvious immunocompromise.4

Culture is not usually useful to evaluate household exposures to molds. Although in vitro diagnostic IgE allergen sensitization testing to molds is available through Quest Diagnostics, such testing is also unnecessary in most cases. Removal of mold from the residence should be curative.

Stachybotrys is a common cause of household mold following water damage. Stachybotrys can also produce mycotoxins that can be internalized by ingestion, inhalation, or absorption through the skin, but clinical testing is not readily available.4

References

  1. Anaissie EJ, McGinnis MR, Pfaller MA, eds. Clinical Mycology. 2nd edition, London, England: Churchill Livingston; 2009:301.
  2. Abdolrasouli A and Howell S. (2023). Processing Specimens for Fungal Culture. In ClinMicroNow. https://doi.org/10.1002/9781683670438.cmph0104
  3. Centers for Disease Control and Prevention. Candida auris (C. auris). www.cdc.gov/candida-auris/about/index.html. Updated April 24, 2024. Accessed December 30, 2024.
  4. Larone DH, ed. Medically Important Fungi: A Guide to Identification. 7th ed, Washington, DC: ASM Press; 2023.

 


This FAQ is provided for informational purposes only and is not intended as medical advice. Test selection and interpretation, diagnosis, and patient management decisions should be based on the clinician’s education, clinical expertise, and assessment of the patient.



Document FAQS.110 Version 1

Version 1: Effective 04/30/2025 to present

Version 0: Effective 06/30/2016 to 04/30/2025

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