Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 511: Which fungus is most commonly associated with orbital cellulitis in patients with diabetic ketoacidosis?

A. Candida
B. Mucor
C. Rhizopus (Correct Answer)
D. Aspergillus

Explanation: ***Rhizopus*** - *Rhizopus* is the most common cause of **mucormycosis** (also called zygomycosis), an aggressive fungal infection that frequently affects immunocompromised patients, especially those with **diabetic ketoacidosis (DKA)**. - *Rhizopus arrhizus* (formerly *R. oryzae*) accounts for approximately **70% of all mucormycosis cases**, making it the single most common causative organism. - In DKA, the acidic environment and high glucose levels favor the growth of **Mucorales fungi**, leading to rapid progression from the sinuses to the orbit and brain (rhinoorbital-cerebral mucormycosis). *Candida* - While *Candida* is a common cause of fungal infections, it typically manifests as **candidemia**, **esophagitis**, or **vulvovaginitis**, and is rarely associated with orbital cellulitis in DKA. - *Candida* infections are more likely in patients with indwelling catheters or those on broad-spectrum antibiotics, rather than specifically linked to DKA-induced orbital cellulitis. *Mucor* - The genus *Mucor* is part of the **Mucorales order** and can cause **mucormycosis** with identical clinical presentations to *Rhizopus*. - However, *Mucor* species account for only **10-20% of mucormycosis cases**, making *Rhizopus* the **most commonly** associated genus as asked in the question. - While both are clinically grouped under "mucormycosis," *Rhizopus* is the more specific and statistically correct answer when identifying the most common causative fungus. *Aspergillus* - *Aspergillus* species are common environmental fungi that can cause invasive infections, particularly in immunocompromised patients, leading to conditions like **aspergilloma** or **invasive aspergillosis**. - While *Aspergillus* can cause sinus and orbital infections, it is less commonly associated with the rapid, aggressive form of orbital cellulitis seen in DKA compared to mucormycosis caused by *Rhizopus*.

Question 512: Which fungus is commonly known as golden yellow jelly fungus?

A. T. tonsurans
B. Tremella mesenterica (Correct Answer)
C. Epidermophyton floccosum
D. T. mentagrophytes

Explanation: ***Tremella mesenterica*** - This fungus is commonly referred to as **golden yellow jelly fungus** or **witch's butter** due to its distinctive golden-yellow, gelatinous, and brain-like appearance. - It is a **jelly fungus** that typically grows on dead hardwood branches, especially after rain, and is known for its pliable, quivering texture. *T. tonsurans* - This refers to **Trichophyton tonsurans**, a dermatophytic fungus primarily known for causing **tinea capitis** (ringworm of the scalp). - Its common name relates to its effect on hair, causing breakage and a "black dot" appearance, rather than a golden yellow, jelly-like form. *Epidermophyton floccosum* - This is a dermatophytic fungus that specifically causes infections of the **skin and nails**, particularly **tinea pedis** (athlete's foot) and **tinea cruris** (jock itch). - It does not produce a fruiting body and is not described as a jelly-like fungus. *T. mentagrophytes* - This refers to **Trichophyton mentagrophytes**, another common dermatophyte responsible for various superficial fungal infections, including **tinea pedis**, **tinea corporis**, and **tinea unguium**. - Its clinical presentation is not that of a golden yellow jelly fungus.

Question 513: Which of the following conditions is NOT caused by Aspergillus?

A. Otomycosis
B. Dermatophytosis (Correct Answer)
C. Allergic sinusitis
D. Bronchopulmonary allergy

Explanation: ***Dermatophytosis*** - This condition is caused by **dermatophytes** (e.g., *Trichophyton*, *Microsporum*, *Epidermophyton*), which are a specific group of fungi that metabolize keratin. - *Aspergillus* species are generally **opportunistic molds** but do not typically cause dermatophytosis, which is a superficial fungal infection of the skin, hair, or nails. *Otomycosis* - **Otomycosis** is a fungal infection of the external ear canal, and *Aspergillus* species are a common cause, particularly *Aspergillus niger*. - It can lead to ear pain, discharge, itching, and hearing impairment. *Allergic sinusitis* - **Allergic fungal sinusitis (AFS)** is a common form of fungal sinusitis where *Aspergillus* species are significant contributors, often leading to a thick, tenacious allergic mucin. - This condition is an IgE-mediated hypersensitivity reaction to the fungal elements in the nasal and sinus cavities. *Bronchopulmonary allergy* - **Allergic bronchopulmonary aspergillosis (ABPA)** is a hypersensitivity reaction to *Aspergillus fumigatus* antigens that colonize the airways, particularly in individuals with asthma or cystic fibrosis. - It results in recurrent episodes of wheezing, cough, and transient pulmonary infiltrates, and can lead to bronchiectasis if left untreated.

Question 514: In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?

A. Aspergillus (Correct Answer)
B. Mucor
C. Penicillium
D. Candida

Explanation: ***Aspergillus*** - *Aspergillus* species are characterized by their distinctive **acute-angled (dichotomous) septate hyphae** when observed microscopically in tissue sections or clinical samples. - This morphological feature is crucial for differentiating *Aspergillus* infections, such as **aspergillosis**, from other fungal infections. *Mucor* - *Mucor* (along with *Rhizopus* and *Lichtheimia*) belongs to the Zygomycetes class, which are characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching, not acute-angled septate hyphae. - These fungi are associated with **mucormycosis**, often seen in immunocompromised patients, particularly those with diabetes. *Penicillium* - *Penicillium* is a common mold known for producing penicillin and typically appears as **septate hyphae** but is more often recognized by its branching, brush-like conidiophores (penicilli) in culture rather than a distinct acute-angled septate hyphal morphology in clinical samples causing invasive disease. - While it can cause opportunistic infections, its hyphae are less commonly described as having uniquely acute angles compared to *Aspergillus*. *Candida* - *Candida* species are typically observed as **yeast cells (oval budding forms)**, often forming **pseudohyphae** (elongated yeast cells that remain attached) or true hyphae under specific conditions, but not as acute-angled septate hyphae. - *Candida* is a common cause of superficial and invasive candidiasis, and its microscopic appearance is distinct from filamentous fungi.

Question 515: Which of the following statements about Penicillium marneffei is incorrect?

A. Forms black colonies (Correct Answer)
B. Is a dimorphic fungus
C. Amphotericin B is used for treatment
D. Causes severe infections in immunocompromised patients

Explanation: ***Forms black colonies*** - *Penicillium marneffei* typically forms colonies that are often **reddish-beige** or **pigmented red-diffusible**, not black. - The production of a characteristic **red-to-burgundy pigment** is a key identifying feature of this fungus, especially in culture. *Is a dimorphic fungus* - This statement is correct. *Penicillium marneffei* is a **thermally dimorphic fungus**, meaning it grows as a mould at 25°C (room temperature) and as yeast-like cells at 37°C (body temperature). - This dimorphism is crucial for its pathogenesis and identification. *Amphotericin B is used for treatment* - This statement is correct. **Amphotericin B** is a commonly used antifungal agent for the treatment of severe *Penicillium marneffei* infections, particularly in immunocompromised patients. - It is often followed by a maintenance regimen with an azole antifungal like itraconazole. *Causes severe infections in immunocompromised patients* - This statement is correct. *Penicillium marneffei* is an **opportunistic pathogen** that primarily causes severe, disseminated infections in individuals with compromised immune systems, especially those with HIV/AIDS. - Endemic regions include Southeast Asia, where it is a leading cause of systemic mycosis in HIV-positive patients.

Question 516: The fungus with septate hyphae and dichotomous branching is?

A. Aspergillus (Correct Answer)
B. Penicillium
C. Mucor
D. Rhizopus

Explanation: ***Aspergillus*** - *Aspergillus* species are characterized by their **septate hyphae** and **acute-angle branching** (branching at approximately 45-degree angles), which are key distinguishing features in histopathology. - This branching pattern is sometimes referred to as "dichotomous branching" in medical literature, though true dichotomous branching is more characteristic of certain tissue forms. - This fungal morphology is often seen in infections such as **invasive aspergillosis** in immunocompromised patients. *Penicillium* - *Penicillium* also has **septate hyphae**, but its branching pattern is typically *not acute-angled or dichotomous*. - It is more commonly known for its **brush-like** conidiophores (penicillus) in culture rather than distinctive tissue branching patterns. *Mucor* - *Mucor* is a type of **zygomycete** (now classified under Mucorales) and is characterized by **aseptate or sparsely septate hyphae** with **irregular, right-angle branching**. - This is a key histological feature distinguishing it from *Aspergillus* in cases of **mucormycosis**. *Rhizopus* - Similar to *Mucor*, *Rhizopus* is also a zygomycete with **aseptate or sparsely septate hyphae** and **irregular, wide-angle branching**. - It is often identified in culture by the presence of **rhizoids** (root-like structures) and sporangiophores.

Question 517: A plant prick can produce sporotrichosis. Which of the following statements about sporotrichosis is false?

A. Enlarged lymph nodes extending centripetally as a beaded chain are a characteristic finding
B. Most cases are acquired via cutaneous inoculation
C. It is an occupational disease of butchers, doctors (Correct Answer)
D. Is a chronic mycotic disease that typically involves skin, subcutaneous tissue and regional lymphatics

Explanation: ***It is an occupational disease of butchers, doctors*** - Sporotrichosis is an **occupational hazard for gardeners, florists, and agricultural workers** due to exposure to decaying plant matter, not typically for butchers or doctors. - The disease is caused by **direct inoculation** of the fungus *Sporothrix schenckii* into the skin, often through a thorn prick or minor trauma. *Most cases are acquired via cutaneous inoculation* - This statement is **true** as sporotrichosis is primarily caused by **traumatic implantation** of fungal spores into the skin. - Common sources include **thorns, splinters, sphagnum moss**, and other plant materials. *Enlarged lymph nodes extending centripetally as a beaded chain are a characteristic finding* - This statement is **true** and describes the classic **lymphocutaneous sporotrichosis**, where lesions and **nodular lymphangitis** track along lymphatic channels. - The "beaded chain" appearance refers to the multiple subcutaneous nodules formed along the lymphatic vessels. *Is a chronic mycotic disease that typically involves skin, subcutaneous tissue and regional lymphatics* - This statement is **true** because sporotrichosis is a **slow-progressing fungal infection** that primarily affects the skin, the tissue just beneath the skin, and the lymphatics draining the infected area. - While systemic dissemination can occur in immunocompromised individuals, the **cutaneous and lymphocutaneous forms** are most common.

Question 518: Which of the following is a cause of Valley fever (desert rheumatism)?

A. Sporothrix
B. Cladosporium
C. Phialophora
D. Coccidioides (Correct Answer)

Explanation: ***Coccidioides*** - **Valley fever**, or desert rheumatism, is caused by infection with the dimorphic fungus **Coccidioides**, primarily **Coccidioides immitis** and **Coccidioides posadasii**. - This fungus is endemic to arid and semi-arid regions, especially the **southwestern United States** and parts of Central and South America. *Sporothrix* - **Sporothrix schenckii** causes sporotrichosis, a chronic fungal infection typically involving the skin, subcutaneous tissue, and adjacent lymphatics, often through skin trauma. - It does not cause Valley fever. *Cladosporium* - **Cladosporium** species are ubiquitous molds commonly found in outdoor and indoor environments, often associated with allergic reactions and occasionally superficial infections. - They are not a cause of Valley fever. *Phialophora* - **Phialophora** species are dematiaceous fungi that can cause phaeohyphomycosis, chromoblastomycosis, and eumycetoma, which are subcutaneous or systemic fungal infections. - They are not associated with Valley fever.

Question 519: Which of the following statements is true regarding dimorphic fungi?

A. Exists in two distinct morphological forms
B. All dimorphic fungi are highly pathogenic to immunocompetent hosts
C. Primarily found in tropical and subtropical regions
D. Transforms between yeast and mold forms at different temperatures (Correct Answer)

Explanation: ***Transforms between yeast and mold forms at different temperatures*** - Dimorphic fungi exhibit **thermal dimorphism**, transitioning between a **mold (mycelial) form** at ambient temperatures (e.g., 25°C) and a **yeast form** at body temperature (e.g., 37°C). - This temperature-dependent morphological switch is the **defining characteristic** of dimorphic fungi and is crucial for their ability to survive in the environment as molds and cause infection in hosts as yeasts. - Examples include **Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis, Sporothrix schenckii, and Talaromyces marneffei**. *Exists in two distinct morphological forms* - While this statement is technically true, it is too general and doesn't capture the **key mechanism** that defines dimorphic fungi. - Many fungi can exist in different forms (e.g., filamentous, yeast-like) but not necessarily in the reversible, **temperature-dependent manner** that specifically defines dimorphic fungi. *All dimorphic fungi are highly pathogenic to immunocompetent hosts* - This is **FALSE**. While dimorphic fungi are pathogenic, their severity varies greatly. - Many dimorphic fungal infections (like histoplasmosis) are **asymptomatic or mild** in immunocompetent individuals and only cause severe disease in immunocompromised patients. - **Blastomycosis and coccidioidomycosis** can cause severe disease in healthy hosts, but many infections are subclinical. *Primarily found in tropical and subtropical regions* - This is **not universally true** for all dimorphic fungi. - While some are endemic to tropical/subtropical regions (**Histoplasma, Paracoccidioides, Talaromyces**), others like **Blastomyces dermatitidis** are more prevalent in temperate regions (Great Lakes, Mississippi River valley). - **Coccidioides** is found in semi-arid regions of southwestern USA and Latin America.

Question 520: What type of spore is produced by Ascomycota during sexual reproduction?

A. Asexual spores
B. Ascospores (Correct Answer)
C. Conidia
D. None of the options

Explanation: ***Ascospores*** - **Ascospores** are the sexual spores produced by fungi belonging to the phylum **Ascomycota** during their sexual reproductive cycle. - These spores are formed inside a sac-like structure called an **ascus** after **karyogamy (nuclear fusion)** and **meiosis**. - Each ascus typically contains **4-8 ascospores** arranged in a characteristic pattern. - Examples of Ascomycota include *Aspergillus*, *Penicillium*, *Candida*, and yeasts like *Saccharomyces*. *Asexual spores* - **Asexual spores** are produced during **asexual reproduction** without the fusion of gametes or meiosis. - Examples include **conidia** and **sporangiospores**, which allow for rapid proliferation and dispersal. *Conidia* - **Conidia** are a specific type of **asexual spore**, not sexual spores. - They are formed exogenously on specialized structures called **conidiophores**. - While Ascomycota can produce conidia asexually, the question asks specifically about sexual reproduction. *None of the options* - This option is incorrect because **ascospores** are indeed the sexual spores of Ascomycota.

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Classification of Fungi

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Superficial Mycoses

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Dermatophytes

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Subcutaneous Mycoses

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Candidiasis

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Aspergillosis

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Cryptococcosis

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Zygomycosis

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Endemic Mycoses

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Opportunistic Fungal Infections

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Antifungal Agents

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Laboratory Diagnosis of Fungal Infections

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Mycology — MCQs

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