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Quizzes > Science

Dimorphic Fungi Quiz: Yeast or Mold?

Quick, free yeast vs mold quiz to test your knowledge. Instant results.

Editorial: Review CompletedCreated By: Kreato MusicUpdated Aug 24, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration of dimorphic fungi yeast and mold forms framing quiz title on teal background

Use this quiz to practice identifying dimorphic fungi that switch between yeast and mold as temperatures change. Get instant feedback to spot gaps, build recall on traits and growth cues, and expand your study with our microbiology quiz and a quick look at protists vs fungi.

Which of the following fungi is a dimorphic organism and causative agent of histoplasmosis?
Candida albicans
Aspergillus fumigatus
Cryptococcus neoformans
Histoplasma capsulatum
Histoplasma capsulatum is a thermal dimorphic fungus that grows as a mold in soil and as a yeast in host tissues, causing histoplasmosis. It is endemic in the Ohio and Mississippi River Valleys and can cause pulmonary and disseminated disease. Candida albicans can exhibit dimorphism in vitro but is primarily an opportunistic pathogen of mucosal surfaces.
At what temperature do most dimorphic fungi convert to their yeast form within the human host?
37°C
25°C
30°C
42°C
Thermal dimorphism refers to the switch from a mold form at environmental temperatures (around 25°C) to a yeast (or spherule) form at body temperature (37°C) in host tissues. This transition is critical for pathogenicity. Temperatures above 40°C may impair fungal growth rather than induce the yeast phase.
Which dimorphic fungus is commonly referred to as the "Chicago disease"?
Paracoccidioides brasiliensis
Blastomyces dermatitidis
Histoplasma capsulatum
Coccidioides immitis
Blastomyces dermatitidis causes blastomycosis, historically known as "Chicago disease" due to its early description in that region. It produces broad-based budding yeast in host tissue. Histoplasma causes Darling's disease, Paracoccidioides causes South American blastomycosis, and Coccidioides causes Valley fever.
In tissue specimens, Coccidioides immitis typically appears as:
Broad-based budding yeast
Tuberculate macroconidia
Multiple-budding yeast (pilot's wheel)
Spherule filled with endospores
Coccidioides immitis forms large spherules containing numerous endospores in tissue. These spherules enlarge and release endospores upon rupture, propagating infection. Broad-based buds are characteristic of Blastomyces, tuberculate macroconidia of Histoplasma, and pilot's wheel budding of Paracoccidioides.
Which of the following is an endemic dimorphic fungus in Latin America, producing a multiple-budding yeast?
Histoplasma capsulatum
Talaromyces marneffei
Paracoccidioides brasiliensis
Sporothrix schenckii
Paracoccidioides brasiliensis causes paracoccidioidomycosis in South and Central America and shows a characteristic pilot's wheel morphology with multiple narrow-based buds. Histoplasma forms small yeasts, Sporothrix forms cigar-shaped yeasts, and Talaromyces (formerly Penicillium) marneffei produces fission yeast.
At 25°C in culture, Sporothrix schenckii typically grows as:
Broad-based budding yeast
Spherule with endospores
Mold with conidia on hyphae
Tuberculate macroconidia
Sporothrix schenckii exhibits a mold form at 25°C with delicate, branching hyphae bearing small conidia in rosettes. In tissue or at 37°C, it assumes a yeast form that is cigar-shaped. This dimorphic shift is important in pathogenesis.
Which fungus was reclassified from Penicillium to Talaromyces and is dimorphic in Southeast Asia?
Coccidioides immitis
Talaromyces marneffei
Blastomyces dermatitidis
Histoplasma capsulatum
Talaromyces marneffei (formerly Penicillium marneffei) is a thermal dimorphic fungus endemic to Southeast Asia. It grows as a mold at 25°C producing red pigment and as a fission yeast at 37°C. This organism primarily affects immunocompromised hosts.
What term describes the ability of fungi to grow as mold in the environment and yeast in host tissues?
Polymorphism
Pleomorphism
Thermotolerance
Thermal dimorphism
Thermal dimorphism is the reversible switch between mold at lower temperatures and yeast (or spherule) at body temperature. This property is a key virulence factor for many systemic pathogenic fungi. Polymorphism and pleomorphism refer more generally to variable shapes.
The disease 'Valley fever' is caused by which dimorphic fungus?
Histoplasma capsulatum
Coccidioides immitis
Paracoccidioides brasiliensis
Blastomyces dermatitidis
Valley fever, or coccidioidomycosis, is caused by Coccidioides immitis (and C. posadasii) and is endemic to the southwestern United States and parts of Mexico. Infection occurs by inhalation of arthroconidia. Other dimorphic fungi cause different systemic mycoses.
Which diagnostic test often detects Histoplasma capsulatum antigen in urine?
Latex agglutination
Galactomannan assay
Beta-D-glucan test
Enzyme immunoassay (EIA)
An enzyme immunoassay (EIA) for Histoplasma antigen in urine and serum is highly sensitive for acute and disseminated histoplasmosis. Galactomannan is used for Aspergillus, and beta-D-glucan is a broad fungal marker. Latex agglutination is less commonly used.
Which dimorphic fungus forms broad-based budding yeast in tissue samples?
Paracoccidioides brasiliensis
Blastomyces dermatitidis
Sporothrix schenckii
Histoplasma capsulatum
Blastomyces dermatitidis produces characteristic broad-based budding yeast in tissue. Paracoccidioides has multiple narrow-based buds, Histoplasma forms small budding yeasts within macrophages, and Sporothrix has cigar-shaped yeasts.
What is the most common route of infection for systemic dimorphic fungi?
Ingestion of spores
Person-to-person contact
Direct skin inoculation
Inhalation of spores or conidia
Most systemic dimorphic fungi infect humans through inhalation of airborne spores or conidia. Once inhaled, they transform to the yeast (or spherule) form in the lungs and may disseminate. Some, like Sporothrix schenckii, can also infect via skin inoculation but this is secondary.
Which of the following is NOT typically a dimorphic fungal pathogen?
Aspergillus fumigatus
Blastomyces dermatitidis
Coccidioides immitis
Histoplasma capsulatum
Aspergillus fumigatus is a mold that does not convert into a yeast form at body temperature and thus is not dimorphic. Histoplasma, Blastomyces, and Coccidioides are classic thermal dimorphic fungi.
What is the characteristic colony morphology of Histoplasma capsulatum at 25°C?
Spherule with endospores
Broad-based budding yeast
Tuberculate macroconidia
Rosette of microconidia
At 25°C, Histoplasma capsulatum grows as a mold producing tuberculate (spiny) macroconidia. Microconidia may also be present but are not tuberculate. These features help differentiate it from other molds.
Which T-helper cell response is most important for controlling systemic dimorphic fungal infections?
Th1 response with IFN-?
Th17 response with IL-17
Treg response with IL-10
Th2 response with IL-4
A Th1 immune response characterized by interferon-gamma production is essential for activating macrophages to kill intracellular dimorphic fungi. Th2 responses are less effective and may worsen disease. Th17 and Treg have roles but are not primary for these pathogens.
Which histological stain best highlights the spherules of Coccidioides in tissue?
Mucicarmine
Periodic acid - Schiff (PAS)
India ink
Gram stain
The PAS stain colors fungal cell walls magenta and is excellent for visualizing Coccidioides spherules and endospores in tissue sections. India ink is used for Cryptococcus, mucicarmine highlights capsule, and Gram stain is less sensitive.
Paracoccidioides brasiliensis yeast cells often show a characteristic appearance termed:
Pilot's wheel
Tuberculate macroconidia
Spherule formation
Broad-based budding
Paracoccidioides brasiliensis yeast cells exhibit multiple narrow-based buds radiating from a central mother cell, resembling a pilot's wheel. This morphology aids histological diagnosis. Other forms are characteristic of different fungi.
What is the first-line oral treatment for mild to moderate blastomycosis?
Voriconazole
Amphotericin B
Fluconazole
Itraconazole
Itraconazole is the recommended first-line oral therapy for mild-to-moderate blastomycosis due to its efficacy and safety profile. Amphotericin B is reserved for severe or CNS disease. Fluconazole has less activity, and voriconazole is not standard for blastomycosis.
Which cell wall component of dimorphic fungi most strongly stimulates macrophage activation?
Melanin
Chitin
Mannoprotein
?-(1,3)-glucan
?-(1,3)-glucan in the fungal cell wall is recognized by pattern recognition receptors on macrophages and dendritic cells, triggering a proinflammatory response. Chitin and mannoproteins are less potent, and melanin is primarily a virulence factor.
In the laboratory, the conversion of a dimorphic fungus from mold to yeast form is confirmed by a:
Antigen detection assay
Agglutination assay
Capsule induction test
Reversal (dimorphism) test
A reversal test involves subculturing the organism from mold to yeast conditions and back to demonstrate true thermal dimorphism. This confirms species identification. Agglutination and antigen tests are diagnostic but do not show morphologic conversion.
Histoplasma capsulatum var. duboisii, causing African histoplasmosis, is primarily found in:
Southeast Asia
Sub-Saharan Africa
Western Europe
North America
Histoplasma capsulatum var. duboisii is endemic to sub-Saharan Africa and causes African histoplasmosis with skin and bone lesions. The classic var. capsulatum is found in the Americas. It differs in clinical presentation and morphology.
Which environmental form of Coccidioides immitis is primarily responsible for infecting humans?
Spherules
Yeast cells
Macroconidia
Arthroconidia
In the environment, Coccidioides immitis grows as a mold producing arthroconidia that become airborne and are inhaled. Inside the host, arthroconidia transform into spherules. Yeast cells and macroconidia are not part of its life cycle.
Which stain is most commonly used to visualize broad-based budding yeast of Blastomyces in clinical specimens?
India ink
Gram stain
Mucicarmine
Gomori methenamine silver (GMS)
GMS stain highlights fungal cell walls in black, making broad-based budding yeast of Blastomyces dermatitidis readily visible against a light background. Gram stain is less sensitive for fungi. India ink and mucicarmine are used for Cryptococcus.
Sporothrix schenckii infection is most often acquired via:
Ingestion of spores
Inhalation of arthroconidia
Person-to-person contact
Traumatic inoculation through plant material
Sporotrichosis, or rose gardener's disease, typically follows traumatic inoculation of Sporothrix schenckii from thorns or plant matter. The fungus then forms subcutaneous nodules. Inhalation and ingestion are not usual routes.
Paracoccidioidomycosis is most prevalent in which population or region?
Midwestern USA
Sub-Saharan Africa
Rural South America
Southeast Asia
Paracoccidioidomycosis is endemic to rural areas of South America, especially Brazil, where the fungus lives in soil. Agricultural workers are at increased risk. It is not found in the other listed regions.
Talaromyces marneffei produces what distinctive diffusible pigment at 25°C?
Green pigment
Yellow pigment
Red pigment
Blue pigment
Talaromyces marneffei produces a characteristic red diffusible pigment when grown at 25°C in culture. This feature helps distinguish it from related species. Other dimorphic fungi do not typically produce this pigment.
Chronic pulmonary coccidioidomycosis can radiographically resemble which other pulmonary disease?
Aspergilloma
Pulmonary tuberculosis
Histoplasmosis
Pneumocystis pneumonia
Chronic pulmonary coccidioidomycosis often leads to cavitary lesions in the lungs that mimic those seen in pulmonary tuberculosis. Both conditions can present with cough, weight loss, and night sweats. Aspergillomas can colonize these cavities but are secondary, and histoplasmosis tends to cause lymphadenopathy.
Which biosafety level is required for culture of Coccidioides species in a reference laboratory?
BSL-1
BSL-3
BSL-4
BSL-2
Because Coccidioides arthroconidia are highly infectious by inhalation, laboratory culture requires Biosafety Level 3 conditions with respiratory protection. BSL-2 is insufficient, and BSL-4 is reserved for the most dangerous agents with no known treatment.
Histoplasma capsulatum evades the host immune response by primarily surviving within which cell type?
Alveolar macrophages
Eosinophils
Dendritic cells
Neutrophils
Histoplasma capsulatum yeasts are phagocytosed by alveolar macrophages and survive intracellularly by modulating the phagosomal environment. This intracellular niche allows dissemination and evasion of other immune defenses. Neutrophils play a role but are less central.
Which transcription factor is critical for regulating the yeast-phase program in Histoplasma capsulatum?
PacC
SREBP
GAL4
RYP1
The RYP1 (Required for Yeast Phase) transcription factor governs the switch to yeast growth in Histoplasma capsulatum at 37°C. Loss of RYP1 prevents yeast-phase differentiation and attenuates virulence. PacC responds to pH, GAL4 regulates galactose metabolism, and SREBP is involved in sterol regulation.
The primary adhesion and virulence factor BAD1 is associated with which dimorphic fungus?
Histoplasma capsulatum
Paracoccidioides brasiliensis
Blastomyces dermatitidis
Coccidioides immitis
BAD1 (Blastomyces adhesin-1) is a cell-surface adhesion molecule that mediates attachment to host cells and modulates immune responses in Blastomyces dermatitidis. It is essential for virulence and is not found in other dimorphic fungi.
Which glycoprotein antigen (gp43) is used in serodiagnosis of which dimorphic fungal infection?
Histoplasmosis
Paracoccidioidomycosis
Coccidioidomycosis
Blastomycosis
The gp43 glycoprotein antigen is secreted by Paracoccidioides brasiliensis and is the basis for serological tests detecting antibodies in paracoccidioidomycosis. It is not used for other systemic mycoses.
How are endospores released in the tissue form of Coccidioides spp.?
Exocytosis
Rupture of spherules
Fragmentation of hyphae
Budding off yeasts
In host tissue, Coccidioides spherules enlarge and then rupture to release numerous endospores, each capable of forming new spherules. This mechanism propagates infection locally. It does not form yeasts or hyphal fragments in tissue.
Which cytokine is essential for granuloma formation during dimorphic fungal infections?
TNF-?
IL-10
IL-17
IL-4
Tumor necrosis factor-alpha (TNF-?) is critical for macrophage activation and maintenance of granulomas that contain dimorphic fungi. Anti - TNF therapies can precipitate reactivation of latent infection. IL-4 and IL-10 are associated with Th2 and regulatory responses, respectively.
Which molecular technique can differentiate Histoplasma capsulatum from Blastomyces dermatitidis in a clinical sample?
Galactomannan assay
ELISA for fungal antigens
PCR targeting ITS region
Western blotting
PCR assays targeting the internal transcribed spacer (ITS) region of ribosomal DNA can specifically identify and differentiate among dimorphic fungi, including Histoplasma and Blastomyces. ELISAs and galactomannan have cross-reactivity and are less specific.
Which serologic assay is most commonly used for early diagnosis of coccidioidomycosis?
Latex agglutination
Indirect immunofluorescence
Western blot
Complement fixation
Complement fixation tests detect Coccidioides-specific antibodies and are commonly used to support early diagnosis and monitor disease severity. Latex agglutination is less used, and immunofluorescence/Western blot have more specialized roles.
Ambient pH influences dimorphic switching in some fungi via which transcription factor?
RYP1
PacC
AP1
HSP90
PacC is a pH-responsive transcription factor that regulates fungal gene expression and morphology in response to ambient pH. It can influence dimorphic transitions in fungi sensitive to pH changes. RYP1 controls temperature response, HSP90 is a heat shock protein, and AP1 regulates oxidative stress. NCBI PacC Function
Candida albicans switches between yeast and hyphal forms through activation of which signaling pathway?
cAMP-PKA pathway
STAT3 pathway
NF-?B pathway
MAPK JNK pathway
The cAMP-protein kinase A (PKA) signaling pathway is a primary regulator of yeast-to-hypha transition in Candida albicans, contributing to virulence. MAPK pathways also play roles but cAMP-PKA is central. NF-?B and STAT3 are host immune pathways.
Talaromyces marneffei infections are most commonly reported in which region?
Europe
South America
Southeast Asia
Sub-Saharan Africa
Talaromyces marneffei is endemic to Southeast Asia, including Thailand, Vietnam, and southern China. It causes penicilliosis, especially in HIV-infected individuals. It is rare outside this region.
What role does the YPS3 gene play in Paracoccidioides brasiliensis?
Regulates iron acquisition
Codes for a secreted protease
Controls ?-glucan synthesis
Mediates thermal tolerance and cell wall remodeling
YPS3 encodes a protein required for adaptation to host temperature and remodeling of the Paracoccidioides cell wall during the yeast phase. Mutants lacking YPS3 show attenuated virulence. It is not directly involved in ?-glucan synthesis, iron uptake, or protease secretion.
Which host pattern recognition receptor specifically recognizes ?-glucan from dimorphic fungi?
Mannose receptor
NOD2
TLR4
Dectin-1
Dectin-1 is a C-type lectin receptor on macrophages and dendritic cells that specifically binds ?-(1,3)-glucan in fungal cell walls, triggering phagocytosis and cytokine production. TLR4 recognizes lipopolysaccharide, NOD2 senses muramyl dipeptide, and the mannose receptor binds mannoproteins.
Which advanced molecular technique is most suited for profiling gene expression changes during the dimorphic transition of Histoplasma capsulatum?
Mass spectrometry proteomics
Quantitative PCR
Western blot analysis
RNA sequencing (RNA-seq)
RNA sequencing (RNA-seq) provides a comprehensive, quantitative profile of transcriptome-wide gene expression, making it ideal for studying the regulatory networks underlying the dimorphic switch in Histoplasma capsulatum. qPCR is limited to targeted genes, while proteomics and Western blot analyze proteins.
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Study Outcomes

  1. Understand Dimorphic Fungi Growth -

    Explain how fungi capable of dimorphism grow either as yeast or mold and the environmental triggers that drive their morphological shifts.

  2. Identify Temperature Preferences -

    Describe the temperature preference of dimorphic fungi and how thermal conditions determine whether they exist in yeast or mold form.

  3. Analyze Infection Modes -

    Differentiate between inhalation, cutaneous, and systemic modes of infection employed by pathogenic dimorphic fungi.

  4. Recognize Unique Yeast Forms -

    Recall specific yeast-to-mold transition fungi and their specialized yeast forms during human infection.

  5. Apply Mycology Dimorphic Fungi Facts -

    Use key mycology dimorphic fungi facts to tackle quiz questions and reinforce your understanding of fungal pathogenesis.

  6. Evaluate Quiz Performance -

    Assess your mastery of dimorphic fungi characteristics by interpreting your quiz score and identifying areas for further study.

Cheat Sheet

  1. Thermal Dimorphism and Temperature Preference -

    Fungi capable of dimorphism grow either as yeasts at 37°C in host tissues and as molds at 25°C in the environment, often remembered with the phrase "Yeast in heat, mold in cold." This thermal dimorphism is regulated by temperature-sensitive gene expression (e.g., DRK1 in Blastomyces) and is central to pathogenicity (CDC, ASM).

  2. Key Dimorphic Pathogens and Mnemonic -

    A useful mnemonic "High Blast Cocci Party Sporadically" helps recall the main dimorphic fungi: Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides spp., Paracoccidioides brasiliensis, and Sporothrix schenckii. Recognizing these fungi capable of dimorphism grow either as environmental molds producing infectious spores or as yeasts/spherules in tissue is essential for diagnosis (University research).

  3. Infection Route and Morphological Shift -

    Dimorphic fungi typically infect via inhalation of mold-form conidia, which then convert to yeast in the lungs to evade immunity; for example, Histoplasma capsulatum conidia inhaled into alveoli transform into budding yeasts. Understanding this yeast to mold transition fungi undergo in hosts explains why respiratory exposure often leads to systemic disease (WHO, medical journals).

  4. Diagnostic Culture and Microscopy -

    When culturing dimorphic fungi, lab technicians grow samples at 25°C to observe mold structures and at 37°C to confirm yeast-phase morphology, a process called the "conversion test." Microscopic features like Blastomyces' broad-based buds and Coccidioides' spherules help distinguish species and inform appropriate treatment (ASM Manual, CDC guidelines).

  5. Clinical Implications and Virulence Factors -

    Thermal dimorphism influences virulence, as the yeast phase expresses surface proteins (e.g., BAD1 in Blastomyces) that facilitate immune evasion. Studying these dimorphic fungi characteristics guides antifungal therapy development and highlights the importance of temperature preference in pathogenesis (peer-reviewed research).

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