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Dermatophytes, molds, fungal biomarkers and Pneumocystis

17 min

  • Confirm a dermatophyte from skin, hair, or nail by colony and microscopic features
  • Distinguish broad pauciseptate from narrow septate hyphal patterns
  • Read galactomannan and beta-D-glucan results against the fungi they miss
  • Report a quantitative Pneumocystis PCR without overcalling pneumonia or colonization

Read the full reference

Try first

Try first

A sinus biopsy shows narrow, regularly septate hyaline hyphae with acute-angle, dichotomous branching invading tissue. What does the laboratory report from the direct examination?

The next section explains it.

Right. The next section explains why.

The next section explains it.

The next section explains it.

The next section explains it.

Get the idea

Report the hyphal pattern

Hyphae invading viable tissue support invasive mold disease. Their shape points to a group of molds.1,2

FeatureMucorales patternAspergillus-like pattern
WidthBroad, ribbon-likeNarrow
SeptaFewRegular
BranchingIrregular, at wide anglesAcute, dichotomous

Folds from tissue processing can look like septa. Fusarium, Scedosporium and other hyaline molds look like Aspergillus in tissue. Culture on medium without cycloheximide, or molecular testing, identifies the mold.1,2

Dermatophytes need more than a color change

Skin scale is collected from the active border of the lesion. KOH shows hyaline septate hyphae and arthroconidia and does not identify a species. A color change on dermatophyte test medium (DTM) is presumptive, because nondermatophyte molds can also alkalinize it. A dermatophyte is reported from colony and microscopic features or a validated identification method.3

What the biomarkers miss

Galactomannan comes from the Aspergillus cell wall, and its sensitivity falls during mold-active therapy. (1→3)-β-D-glucan rises in several invasive fungal diseases and in Pneumocystis pneumonia, and it names no organism. Hemodialysis materials, blood products and glucan-containing gauze can raise it falsely. Mucorales and Cryptococcus often produce little detectable β-D-glucan, and Mucorales produce no detectable galactomannan. Negative biomarkers leave mucormycosis and other rare mold infections possible.2,4

Reading a Pneumocystis PCR

Pneumocystis jirovecii has no routine clinical culture, and lower respiratory specimens give the best yield. Quantitative PCR is more sensitive than staining. No universal cutoff separates pneumonia from colonization. A high burden supports disease in a compatible host. A low positive result can mean early infection, resolving infection or colonization, and burden often runs lower in patients without HIV. A low serum β-D-glucan makes Pneumocystis pneumonia less likely.5

References
  1. Patterson TF, Thompson GR III, Denning DW, et al. Practice guidelines for the diagnosis and management of aspergillosis: 2016 update by the Infectious Diseases Society of America. Clin Infect Dis. 2016;63(4):e1-e60. doi:10.1093/cid/ciw326
  2. Cornely OA, Alastruey-Izquierdo A, Arenz D, et al. Global guideline for the diagnosis and management of mucormycosis: an initiative of the European Confederation of Medical Mycology in cooperation with the Mycoses Study Group Education and Research Consortium. Lancet Infect Dis. 2019;19(12):e405-e421. doi:10.1016/S1473-3099(19)30312-3
  3. Tille PM. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2021.
  4. Donnelly JP, Chen SC, Kauffman CA, et al. Revision and update of the consensus definitions of invasive fungal disease from the European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium. Clin Infect Dis. 2020;71(6):1367-1376. doi:10.1093/cid/ciz1008
  5. Panel on Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents With HIV. Pneumocystis pneumonia. National Institutes of Health. Accessed September 27, 2026. https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/pneumocystis

Watch one

Skin scale from the active border of a scaly foot lesion is cultured. The KOH-calcofluor preparation showed hyaline septate hyphae. On day 7 the DTM has turned red, and a white, cottony colony grows on the nonselective fungal medium. A tape mount made in the biological safety cabinet shows small teardrop-shaped microconidia along the sides of the hyphae and no macroconidia. What do you report?

  1. Check the specimen: scale from the active border.

    The advancing edge holds viable organisms, and the healing center holds few.

  2. Read the direct preparation: hyaline septate hyphae.

    Hyaline septate hyphae in skin support a dermatophyte. KOH cannot give a species.

  3. Read the DTM: red, and presumptive only.

    Nondermatophyte molds can also turn DTM red, so the color change is presumptive.

  4. Read the colony microscopy.

    Small pyriform microconidia along the hyphae fit the Trichophyton rubrum complex. The T. mentagrophytes/interdigitale complex forms round microconidia in clusters, and Epidermophyton floccosum forms club-shaped macroconidia and no microconidia.

  5. Report at the level the features support.

    Morphology supports a species complex. Forcing a name past what the features show can be wrong.

Report Trichophyton rubrum complex, from the colony and microscopic features. The red DTM alone would not have supported a dermatophyte report.

Your turn

Problem 1 of 3

A sinus biopsy shows broad, ribbon-like, irregularly branching hyphae with few septa invading viable tissue and vessel walls. What does the laboratory report from the direct examination?

Incorrect. Width and branch angle vary, and processing folds can create false septa or misleading angles, so no genus is identified from tissue geometry.

Incorrect. Aspergillus-like hyphae are narrow, regularly septate, and branch at acute angles. Broad, ribbon-like hyphae with few septa and haphazard branching are the Mucorales pattern.

Correct. Ribbon-like hyphae with few septa and irregular branching are the Mucorales pattern, and invasion of viable tissue supports invasive mold disease. Culture on medium without cycloheximide and, when culture fails, molecular testing identify the genus.

Hint
  1. Look at width, septa and branching together.
  2. Ask how far tissue geometry can go toward a name.

Review Mucorales

Problem 2 of 3

Serum galactomannan and (1→3)-β-D-glucan are both negative in a patient with diabetic ketoacidosis and suspected rhino-orbital mucormycosis. How are these results interpreted?

Correct. Mucorales produce little galactomannan or β-D-glucan, so negative biomarkers leave mucormycosis possible. Direct examination, histopathology, and culture of involved tissue answer the question.

Incorrect. Mucorales typically produce little of either analyte, so negative results leave mucormycosis and other rare mold infections possible.

Incorrect. A negative galactomannan leaves invasive aspergillosis possible too, particularly during mold-active therapy.

Hint
  1. Consider which fungi release each analyte.
  2. Ask how much galactomannan and β-D-glucan Mucorales release into serum.

Review Fungal biomarkers and antigen tests

Problem 3 of 3

A toenail culture turns DTM red on day 4. The colony is gray-green and powdery. A tape mount made in the cabinet shows conidiophores ending in swollen vesicles with chains of conidia. What do you report?

Nondermatophyte molds can also turn DTM red. The colony and microscopy here point to a different mold.

Reported a dermatophyte from a DTM color change alone

A color change on dermatophyte test medium is presumptive, because nondermatophyte molds can also alkalinize the medium. Colony and microscopic features or a validated identification method are needed before a dermatophyte is reported.

Vesicles bearing chains of conidia are Aspergillus conidial heads. Its significance in a nail depends on repeated recovery and direct findings.

T. rubrum forms small pyriform microconidia along the hyphae and no vesicles.

E. floccosum forms smooth, club-shaped macroconidia in clusters.

Review Dermatophytes

Use it

  • Beatrix Holmgren, 58, MRN 2074386, is a retired choir director receiving chemotherapy for lymphoma.
  • She takes a mold-active azole as prophylaxis and has no HIV infection.
  • She now has fever, a dry cough and falling oxygen saturation.
  • Bronchoalveolar lavage (BAL) fluid goes for a quantitative Pneumocystis jirovecii PCR, and serum goes for fungal biomarkers.
TestResultPreviousReference intervalFlag
Galactomannan0.2Less than 0.5
(1→3)-β-D-glucan240 pg/mLLess than 60 pg/mLHigh
P. jirovecii PCR, BALDetected, low positiveNot detected

Specimen: H 1, L 2, I 1. Serum. BAL fluid sent separately for PCR.

Decision 1 of 3

What does the negative galactomannan tell the reader?

Galactomannan sensitivity falls during mold-active therapy, and she takes a mold-active azole.

Mucorales produce no detectable galactomannan, and the azole lowers sensitivity for Aspergillus.

Reported mucormycosis excluded on negative biomarkers

Mucorales produce no detectable galactomannan, Mucorales and Cryptococcus produce little beta-D-glucan, and galactomannan sensitivity falls during mold-active therapy. Negative results therefore leave mucormycosis and other rare molds possible, and tissue examination and culture are used to look for them.

On mold-active therapy a negative galactomannan leaves aspergillosis possible, and it never addressed mucormycosis.

Review Fungal biomarkers and antigen tests

Decision 2 of 3

What does the β-D-glucan of 240 pg/mL add?

β-D-glucan is a panfungal marker that often rises in Pneumocystis pneumonia. It cannot say which fungus is present, and blood products or dialysis materials can raise it.

β-D-glucan comes from many fungi. The PCR is the organism-specific result here.

An elevated β-D-glucan is not specific to Aspergillus.

Review Fungal biomarkers and antigen tests

Decision 3 of 3

How is the low-positive PCR reported?

A low positive can mean early or resolving infection or colonization. The PCR value alone does not establish pneumonia.

Reported a low-positive Pneumocystis PCR as pneumonia

A low-positive quantitative PCR can mean early or resolving infection or colonization, and no universal cutoff separates them. Calling it pneumonia claims more than the result shows, and dismissing it as colonization can miss disease in a patient without HIV, whose organism burden is often lower.

Burden often runs lower in patients without HIV, so a low positive can still be pneumonia. Dismissing it can miss disease.

No universal cutoff separates pneumonia from colonization. The care team reads the value with her immune status, imaging and the elevated β-D-glucan.

Review Pneumocystis

The clue that settled this case is the host. Mold-active prophylaxis lowers galactomannan sensitivity, so the negative leaves aspergillosis possible. Without HIV infection, Pneumocystis burden runs lower, so the low-positive PCR is reported as a value to read with her elevated β-D-glucan and her risk.

Keep

Sources checked