Mycology Practice Questions

Q: Dermatophytes affect -

Keratin. ***Keratin*** - **Dermatophytes** are a group of fungi that have a unique ability to digest **keratin**, a protein found in **skin, hair, and nails**. - This characteristic allows them to colonize and thrive in these superficial tissues, causing infections like **tinea corporis** (ringworm) or **tinea pedis** (athlete's foot). *Dermis of skin* - The **dermis** is the layer of skin beneath the epidermis, rich in **collagen, elastin, blood vessels, and nerves**. - Dermatophytes do not typically invade the dermis; their infections are generally limited to the **stratum corneum** and other keratinized structures. *Stratum spongiosum* - **Stratum spongiosum** is a term sometimes used to describe an edematous (swollen) epidermis, often seen in **eczema** and **dermatitis**. - Dermatophytes do not target this specific architectural change in the epidermis but rather feed on the keratin present in the more superficial layers. *Stratum basal* - The **stratum basale** (also called stratum germinativum) is the deepest layer of the **epidermis**, responsible for cell division and producing new skin cells. - Dermatophytes primarily infect the **dead keratinized cells** of the stratum corneum rather than the metabolically active cells of the stratum basale.

Q: A 60-year-old female, known case of rheumatoid ahritis presented to the ER with shoness of breath, fever and cough for 2 days. Patient was staed on infliximab 2 months ago. On examination, Hypotension Hypoxemic Not maintaining spO2 on room air. Patient was diagnosed with respiratory failure and put on mechanical ventilation. Bronchioalveolar lavage was done and subjected to silver staining. Chest x-ray What is the most likely diagnosis in the above condition: -

Histoplasma. **Histoplasma** - Given the history of **rheumatoid arthritis** and **infliximab** use, the patient is immunocompromised and susceptible to opportunistic infections. Exposure to certain geographic regions endemic for **Histoplasma** (e.g., Ohio and Mississippi River valleys) along with a positive silver stain from BAL, suggests **Histoplasma** as a likely diagnosis. - **Silver stain** (e.g., GMS stain) is commonly used to identify **fungal organisms** like *Histoplasma capsulatum* in tissue or BAL samples. *Aspergillus* - While *Aspergillus* can cause severe lung infections in immunocompromised patients, it typically presents with distinct chest imaging findings such as **halo sign** or **air crescent sign**. - **Silver stain** can identify *Aspergillus*, but the presentation context leans more towards *Histoplasma* given the common reactivation in immunocompromised states. *Mycobacterium tuberculosis* - **Tuberculosis** should be considered in immunocompromised patients, but it is typically diagnosed with **acid-fast bacillus (AFB) stain** or culture, not silver stain. - The acute onset of severe respiratory failure is less typical for primary or reactivated TB, which often has a more subacute or chronic course. *CMV* - **Cytomegalovirus (CMV) pneumonitis** is a common opportunistic infection in immunocompromised individuals. - However, **CMV** is a virus and would be identified by specific viral staining (e.g., **immunohistochemistry**) or PCR, not by **silver stain**, which targets fungal elements.

Q: Tinea versicolor is caused by:

Malassezia furfur. ***Malassezia furfur*** - **Tinea versicolor** is a superficial fungal infection caused by **Malassezia species**, primarily *Malassezia furfur*. - These fungi are part of the normal skin flora but can become pathogenic under certain conditions, leading to characteristic **hypopigmented or hyperpigmented patches**. *Candida* - **Candida species** are yeasts that typically cause infections like **oral thrush**, **vaginal candidiasis**, and **diaper rash**, not tinea versicolor. - While they can cause skin infections, their clinical presentation differs significantly from the **pigmentation changes** seen in tinea versicolor. *Trichophyton rubra* - **Trichophyton rubra** is a common dermatophyte responsible for various **tinea infections** such as **tinea pedis (athlete's foot)** and **tinea unguium (onychomycosis)**. - It does not cause tinea versicolor, which is caused by a different genus of fungi. *Trichophyton mentagrophytes* - **Trichophyton mentagrophytes** is another dermatophyte that causes common **ringworm infections** like **tinea corporis** and **tinea barbae**. - Its infections are characterized by **erythematous, scaly, and pruritic lesions**, distinct from the macular lesions of tinea versicolor.

Q: Which one of the following diseases is endogenous in origin-

Candidiasis. ***Candidiasis*** - **Candidiasis** is an **endogenous** infection because it is caused by species of *Candida*, especially *Candida albicans*, which is part of the normal human microbiota (e.g., in the oral cavity, gastrointestinal tract, and vagina). - Infection occurs when there is an imbalance in the host's immune system or a disruption in the normal flora, allowing *Candida* to overgrow and cause disease. *Aspergillosis* - **Aspergillosis** is typically an **exogenous** infection caused by inhaling **spores of *Aspergillus*** species, which are ubiquitous in the environment (e.g., soil, decaying vegetation, air). - It is not caused by organisms that are part of the normal human microbiota. *All of the above* - This option is incorrect because aspergillosis and phycomycosis are primarily exogenous infections, not endogenous. *Phycomycosis* - **Phycomycosis** (now more commonly referred to as mucormycosis or zygomycosis) is an **exogenous** infection resulting from inhalation or inoculation of **spores of fungi** belonging to the Mucorales order, which are found in the environment (e.g., soil, decaying matter). - These fungi are not part of the normal human microbiota.

Q: An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?

Microsporum canis. ***Microsporum canis*** - This dermatophyte species is a common cause of **tinea capitis** in children, characterized by **patches of alopecia** and **pruritus**. - **Microsporum** species are known to exhibit **bright blue-green fluorescence** under a Wood's lamp due to the production of pteridine, which aids in diagnosis. *Epidermophyton floccosum* - This fungus primarily causes **tinea pedis**, **tinea cruris**, and **tinea corporis**, but rarely **tinea capitis**. - Infections caused by *Epidermophyton floccosum* typically do **not fluoresce** under a Wood's lamp. *Candida albicans* - *Candida albicans* is a yeast that causes superficial infections like **oral thrush**, **diaper rash**, and **vaginitis**, but it is **not a common cause of tinea capitis**. - *Candida* infections do **not show fluorescence** with a Wood's lamp. *Trichophyton tonsurans* - This is a common cause of **tinea capitis** (especially in the US), often presenting as **"black dot" tinea capitis** due to hair shaft breakage at the scalp surface. - Infections by *Trichophyton tonsurans* typically do **not fluoresce** under a Wood's lamp, differentiating it from *Microsporum* infections.

Q: Which of the following is most likely to be acquired by traumatic inoculation?

Sporothrix schenckii. ***Sporothrix schenckii*** - **Sporothrix schenckii** causes **sporotrichosis** (rose gardener's disease), which is classically acquired through **traumatic inoculation** via thorns, splinters, or plant material contaminated with the fungus. - This dimorphic fungus exists in soil and vegetation, and the mode of transmission is characteristically associated with **gardeners, farmers, and florists** who experience penetrating injuries during their work. - Presents as lymphocutaneous infection with nodular lesions along lymphatic channels. *Histoplasma capsulatum* - Causes histoplasmosis and is endemic to certain regions (Ohio and Mississippi River valleys). - Primarily acquired through **inhalation of microconidia** from soil contaminated with bird or bat droppings, not through traumatic inoculation. - Presents as pulmonary infection in most cases. *Coccidioides immitis* - Causes coccidioidomycosis (Valley Fever) and is found in arid regions of southwestern United States. - Acquired through **inhalation of airborne arthroconidia** from disturbed soil, not through traumatic inoculation. - While rare cases of primary cutaneous infection can occur, inhalation remains the typical route. *Aspergillus fumigatus* - Ubiquitous environmental mold associated with decaying organic matter. - Primarily causes disease through **inhalation of conidia**, leading to allergic reactions, aspergilloma, or invasive aspergillosis in immunocompromised patients. - Not typically associated with traumatic inoculation as the primary mode of infection.

Q: Which is not a dimorphic fungus?

Pneumocystis jirovecii. **Pneumocystis jirovecii** * **Pneumocystis jirovecii** is an **atypical fungus** that does not exhibit dimorphism; it solely exists in a **trophic form** and a **cystic form**, both of which are obligate parasites in the host. * It is classified on genetic findings as a fungus but lacks characteristic fungal cell wall components like ergosterol, making it unique and not a dimorphic fungus. * *P. marneffi* (now *Talaromyces marneffei*) * *P. marneffei* is a **thermally dimorphic fungus** that grows as molds at 25°C with characteristic **red pigment production** and as yeast cells at 37°C. * It causes penicilliosis, an **opportunistic infection** particularly in immunocompromised individuals. * *Histoplasma capsulatum* * *Histoplasma capsulatum* is a **thermally dimorphic fungus** that grows as a mold with tuberculate macroconidia in soil and converts to small, oval budding yeasts at 37°C in host tissues. * It is known for causing **histoplasmosis**, often acquired through inhalation of spores from bird or bat droppings. * *Blastomyces dermatitidis* * *Blastomyces dermatitidis* is a **thermally dimorphic fungus** that grows as a filamentous mold in the environment and as large, **broad-based budding yeast** cells at body temperature in host tissues. * It causes **blastomycosis**, which can manifest as pulmonary, cutaneous, or disseminated disease.

Q: Which test is most specific for diagnosing invasive aspergillosis?

Galactomannan test. ***Galactomannan test*** - The **galactomannan test** detects a polysaccharide component of the *Aspergillus* cell wall, making it specific for *Aspergillus* species. - A positive result, especially in high-risk patients, strongly indicates **invasive aspergillosis** due to its high specificity. *Culture* - While culture can identify *Aspergillus*, it lacks specificity as it can grow as a **contaminant** in respiratory samples. - Recovery of *Aspergillus* from routine cultures does not always confirm invasive disease, often requiring additional evidence. *Beta-D-glucan assay* - The **beta-D-glucan assay** detects a pan-fungal cell wall component, meaning it is not specific to *Aspergillus*. - A positive result can indicate a wide range of **invasive fungal infections**, including candidiasis and pneumocystosis, but does not differentiate them. *Microscopy* - Microscopic examination can reveal **fungal elements** consistent with *Aspergillus* (e.g., septate hyphae with acute angle branching). - However, morphology alone is not definitive and requires confirmatory tests for species identification and to distinguish from other filamentous fungi.

Q: Which of the following exists as yeast at 37°C and hyphae at 25°C?

Histoplasma capsulatum. ***Histoplasma capsulatum*** - This fungus is **thermally dimorphic**, growing as **yeast** at body temperature (37°C) in the host and as **hyphae (mold)** at cooler temperatures (25°C). - This is the **classic example** taught for thermal dimorphism in medical mycology. - Causes **histoplasmosis**, endemic in Ohio and Mississippi river valleys; presents with pulmonary disease and can disseminate in immunocompromised patients. - Laboratory identification relies on this characteristic temperature-dependent growth pattern. *Sporothrix globosa* - This fungus is also thermally dimorphic with the same pattern: **yeast at 37°C** and **hyphae at 25°C**. - Causes **sporotrichosis** (rose gardener's disease), typically presenting as lymphocutaneous infection. - While medically correct, **Histoplasma capsulatum** is the more commonly referenced example in standard medical textbooks for this specific thermal dimorphism pattern. *Cryptococcus neoformans* - Exists primarily as an **encapsulated yeast** at both temperatures. - Does **not** exhibit thermal dimorphism; remains in yeast form in both host and environment. *Candida albicans* - Exhibits dimorphism but grows as **yeast** at most temperatures and forms **pseudohyphae/germ tubes at 37°C** in response to serum and other factors. - Does not follow the classic thermal dimorphism pattern of yeast at 37°C and mold at 25°C.

Q: A biopsy of a lung nodule from a patient with a history of bird exposure reveals yeast cells with thick capsules. What is the most likely pathogen?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - The presence of **yeast cells with thick capsules** is a classic histological finding for *Cryptococcus neoformans*. - While *Cryptococcus* commonly affects immunocompromised individuals, it can also be found in **bird droppings**, particularly from pigeons, making the history of bird exposure relevant. *Aspergillus fumigatus* - *Aspergillus fumigatus* typically presents as **hyphae**, not yeast cells, and would not have a thick capsule. - Infections often manifest as **aspergillomas** (fungus balls) in lung cavities or invasive disease in immunocompromised patients. *Blastomyces dermatitidis* - *Blastomyces dermatitidis* appears as **large, broad-based budding yeast cells** but does not possess a thick capsule. - It is typically found in the **soil**, especially in moist areas, and its association with bird exposure is not as strong as with *Cryptococcus*. *Histoplasma capsulatum* - *Histoplasma capsulatum* is characterized by **small intracellular yeast forms** within macrophages and does not have a thick capsule. - It is strongly associated with **bird and bat droppings** but its microscopic appearance is distinct from that described.

Question 1

Dermatophytes affect -

Accepted Answer

Keratin

Answer

Dermis of skin

Answer

Stratum spongiosum

Answer

Stratum basale

Question 2

A 60-year-old female, known case of rheumatoid ahritis presented to the ER with shoness of breath, fever and cough for 2 days. Patient was staed on infliximab 2 months ago. On examination, Hypotension Hypoxemic Not maintaining spO2 on room air. Patient was diagnosed with respiratory failure and put on mechanical ventilation. Bronchioalveolar lavage was done and subjected to silver staining. Chest x-ray What is the most likely diagnosis in the above condition: -

Accepted Answer

Histoplasma

Answer

Aspergillus

Answer

Mycobacterium tuberculosis

Answer

CMV

Question 3

Tinea versicolor is caused by:

Accepted Answer

Malassezia furfur

Answer

Candida

Answer

Trichophyton rubra

Answer

Trichophyton mentagrophytes

Question 4

Which one of the following diseases is endogenous in origin-

Accepted Answer

Candidiasis

Answer

Aspergillosis

Answer

Phycomycosis

Answer

All of the above

Question 5

An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?

Accepted Answer

Microsporum canis

Answer

Epidermophyton floccosum

Answer

Candida albicans

Answer

Trichophyton tonsurans

Question 6

Which of the following is most likely to be acquired by traumatic inoculation?

Accepted Answer

Sporothrix schenckii

Answer

Coccidioides immitis

Answer

Histoplasma capsulatum

Answer

Aspergillus fumigatus

Question 7

Which is not a dimorphic fungus?

Accepted Answer

Pneumocystis jirovecii

Answer

P. marneffi

Answer

Histoplasma capsulatum

Answer

Blastomyces dermatitidis

Question 8

Which test is most specific for diagnosing invasive aspergillosis?

Accepted Answer

Galactomannan test

Answer

Culture

Answer

Beta-D-glucan assay

Answer

Microscopy

Question 9

Which of the following exists as yeast at 37°C and hyphae at 25°C?

Accepted Answer

Histoplasma capsulatum

Answer

Cryptococcus neoformans

Answer

Sporothrix globosa

Answer

Candida albicans

Question 10

A biopsy of a lung nodule from a patient with a history of bird exposure reveals yeast cells with thick capsules. What is the most likely pathogen?

Accepted Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Blastomyces dermatitidis

Answer

Histoplasma capsulatum

Mycology — MCQs

Mycology — MCQs

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