Mycology – Fungal Culture – Superficial/Dermatophytes

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Background
This page provides superficial culture testing information for dermatophytes and other organisms causing superficial infections at Public Health Ontario (PHO). Dermatophytes are the causative agents of ringworm (tinea), onychomycosis and dermatophytosis. As well, there are many non-dermatophyte organisms that may cause superficial infections such as erythrasma and pityriosis versicolor.

This page is for information specific to superficial fungal culture. For information regarding other testing options, refer to the following PHO webpages:

Updates
Information about diagnostic testing for erythrasma is now included in this test information sheet.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 13 déc. 2024.

Content/Testing Indications

Suspicion of superficial fungal infection, including those that have not been resolved with topical treatments.

Acceptance/Rejection Criteria

Swabs are not a suitable method to collect specimens for superficial culture and will be rejected.

Requests for susceptibility testing of dermatophytes is not a routine test and requires prior approval with the PHO Microbiologist. Please call Customer Service Centre for more information 1-877-604-4567.

Content/Specimen Collection and Handling

Content/Specimen Requirements

Content/Test Requested	Content/Required Requisitions	Content/Specimen Type	Content/Minimum Volume Required	Content/Collection Kit
Superficial microscopy and fungal culture (for dermatophytes)	General Test Requisition	- Skin scrapings - Nail scrapings /clippings - Hair (root ends)	Visible on the black paper collection kit (see submission and collection note # 3 below)	Fungus Culture Kit (Order # 390048)
Rule out erythrasma	General Test Requisition	Skin scrapings from intertriginous areas (i.e. axilla , anogenital regions, skin folds of the breasts, between toe of finger digits)	Visible on the black paper collection kit (see submission and collection note # 3 below)	Fungus Culture Kit (Order # 390048)
Rule out erythrasma	General Test Requisition	- Hair (root ends) - Skin scraping from body trunk (i.e. back , chest), neck, arms, face	Visible on the black paper collection kit (see submission and collection note # 3 below)	Fungus Culture Kit (Order # 390048)

Content/Submission and Collection Notes

Complete all fields of the requisition form, fields a-d are mandatory.

Test(s) requests and indications for testing
Specimen source (with details e.g., skin scraping from which part of the body)
Collection date and time
Immune status – VERY important to note on the requisition if patient has had a transplant, has a haematological malignancy, or is otherwise immunocompromised (including burn wounds, diabetes etc.) as this will impact work up and reporting practices
Current antifungal therapy and/or clinical diagnosis.
Requests for specific organisms of concern (Trichophyton indotineae, erythrasma, tinea versicolor etc.)
Any indications of previous treatment and/or treatment failure.

For clinical specimens, label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

Quantity of specimen is crucial – the greater the amount of specimen, the higher the chance of isolating the causative agent.

Content/Limitations

Specimen volume must be adequate to perform both direct microscopy and culture. Refer to special instructions below on how low volume or low quantity specimens are handled.
If specimen does not have specified source and type, appropriate laboratory examination technique may not be applied.

Content/Storage and Transport

Specimens should be stored at room temperature following collection and shipped to Public Health Ontario as soon as possible. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Content/Special Instructions

Please specifically note on the requisition if you are looking to rule-out erythrasma or tinea versicolor (TV). If sufficient specimen is received, fungal culture will also be performed to detect agents of superficial mycoses and to rule out possible double infections.

Specimens received for rule-out erythrasma or TV that are deemed to be of low volume/quantity will have microscopy prioritized as these organisms are detectable via microscopic exam only.

Specimens received for superficial fungal culture that are deemed to be of low volume/quantity will have culture prioritized.

Content/Requisition and Kit Ordering

Content/Test Frequency and Turnaround Time

Superficial fungal culture is performed Monday to Friday at Public Health Ontario’s laboratory – Toronto, Orillia , Thunder Bay and Timmins sites

The erythrasma test is done daily Monday to Friday at PHO’s laboratory Toronto only.

Turnaround Time for microscopy: 4 business days from receipt at PHO’s laboratory sites.

Turnaround Time for culture report: minimum of 10 business days (2 weeks) from receipt at PHO’s laboratory sites.

Turnaround Time for Identification of isolates grown in culture: dependent on the organism(s)

Content/Test Methods Title

Direct microscopic examination of specimens received for ruling-out superficial fungi and or tinea versicolor is performed using calcofluor-white and potassium hydroxide, while specimens received for ruling-out erythrasma is performed in addition of using modified methylene blue stain.

Erythrasma is not a fungal infection. Rather, it is caused by a bacterium called Corynebacterium minutissimum. However, diagnosis is typically completed in the Mycology Laboratory.

Identification of yeasts and filamentous fungi isolated in culture uses various conventional phenotypic methods, including microscopic morphologic examination, interpretation of biochemical reactions and API strips reaction, growth temperature and culture morphologic characteristics. Molecular methods such as sequencing and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) will be used when phenotypic methods shows result discrepancy.

Content/Test Algorithm

If sufficient quantity of specimen is available, both direct microscopy and culture are performed simultaneously. If quantity is not sufficient, priorities are determined based on what is requested specifically to be ruled-out. Refer to the special instruction above on how examinations are prioritized when a specimen with low quantity is received.

Yeast identification is not routine unless seen in the direct microscopic exam or for patients who are immunocompromised.

Content/Test Interpretation

The following table provides possible test results with associated interpretations:

Microscopic Result	Interpretation	Final Report Comment
Characteristic of Corynebacterium minutissimum, causative agent of erythrasma	Erythrasma confirmed.	Final report based on direct microscopy. Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Suggestive of Corynebacterium minutissimum, causative agent of Erythrasma	Possible erythrasma	Final report based on direct microscopy. Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Negative for erythrasma	Erythrasma ruled-out.	Final report based on direct microscopy. Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Characteristic of Malassezia furfur, causative agent of pityriasis versicolor (tinea versicolor, TV)	Pityriasis versicolor (tinea versicolor, TV) confirmed.	Final report based on direct microscopy. Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Suggestive of Malassezia furfur, causative agent of pityriasis versicolor (tinea versicolor, TV)	Possible pityriasis versicolor (tinea versicolor, TV)	Final report based on direct microscopy. Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Negative for pityriasis versicolor (tinea versicolor, TV)	Possible pityriasis versicolor (tinea versicolor, TV)ruled-out.	Culture will be performed and clients will only be notified if a fungus of significance is isolated.
Mycelium seen Fungal spores and mycelium seen	Suggestive of dermatophyte present	Identification of isolate(s) grown in culture to genus/species.
Fungal Filaments seen Irregular mycelium seen Yeast cells and filaments seen Budding yeast cells seen	Presence of yeast or non-dermatophytic fungi in specimen. Clinical significance is unknown/of some debate.	Dermatophytes will be ruled-out or identified to genus/species if isolated. Non-dermatophyte organisms that are known to cause onychomycosis will be identified to genus/species. Clinically insignificant growth may be reported as ‘non dermatophyte isolated’ or ‘mixture of non dermatophytes isolated’.

Grown cultures are identified up to genera and species level when applicable.

Content/Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Content/References

Clinical and Laboratory Standards Institute (CLSI). Principles and Procedures for Detection and Culture of Fungi in Clinical Specimens. 2nd ed. CLSI guideline M54 (ISBN 978-1-68440-098-0 {Print}; ISBN 978-1-68440-099-7 {Electronic}). Clinical and Laboratory Standards Institute; 2021
Hazen, K., Howell, S.A.. Mycology and antifungal susceptibility testing. In: Leber, A.M. Editor. Clinical Microbiology Procedures Handbook. 4th ed. Washington, D.C.; ASM Press; 2016.
de Hoog, G.S., Guarro, J., Gene, J., Ahmed, S.A., Al-Hatmi, A.M.S., Figueras, M.J., Vitale, R.G.. Atlas of Clinical Fungi. 4th ed. Hilversum; Foundation Atlas of Clinical Fungi; 2020.
Kane, J., Summerbell, R., Sigler, L., Krajden, S., Land, G.. Laboatory Handbook of Dermatophytes: A Clinical Guide and Laboratory Manual of Dermatophytes and Other Filamentous Fungi from Skin, Hair and Nails. USA: Star Publishing Company; 1997