Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 491: What type of microorganism is Cryptococcus neoformans?

A. Bacteria
B. Virus
C. Fungus (Correct Answer)
D. Parasite

Explanation: ***Fungus*** - *Cryptococcus neoformans* is an encapsulated **yeast** that is a common cause of fungal infections, particularly in immunocompromised individuals. - It is known to cause **cryptococcosis**, which can manifest as pneumonia or meningoencephalitis. *Bacteria* - Bacteria are **prokaryotic organisms** and do not possess a true nucleus or membrane-bound organelles, unlike *Cryptococcus neoformans*. - They are typically much smaller than fungi and have distinct cell wall compositions. *Virus* - Viruses are **acellular infectious agents** that require a host cell to replicate; they are not living organisms in the traditional sense. - They are significantly smaller than fungi and lack cellular structures such as a cell wall or organelles. *Parasite* - Parasites are **eukaryotic organisms** that live on or in a host and obtain nutrients at the host's expense, often involving complex life cycles. - While both are eukaryotes, fungi like *Cryptococcus neoformans* are distinct from parasitic protozoa or helminths in their biology and infectious mechanisms.

Question 492: In an immunocompromised patient with pulmonary symptoms, bronchoalveolar lavage reveals septate hyphae with acute angle branching. What is the likely pathogen?

A. Aspergillus fumigatus (Correct Answer)
B. Mucor species
C. Histoplasma capsulatum
D. Candida albicans

Explanation: ***Aspergillus fumigatus*** - The presence of **septate hyphae with acute angle branching** on bronchoalveolar lavage is a classic microscopic finding for *Aspergillus* species, particularly *A. fumigatus*, in immunocompromised patients with pulmonary symptoms. - *Aspergillus* infections often present as **invasive pulmonary aspergillosis** in severely immunocompromised individuals, leading to pneumonia and other lung pathologies. *Mucor species* - *Mucor* species are characterized by **broad, ribbon-like, aseptate or sparsely septate hyphae with irregular, wide-angle branching** (typically 90 degrees), which differs from the acute angle branching seen in *Aspergillus*. - They are known to cause **mucormycosis**, often presenting as rhinocerebral, pulmonary, or cutaneous infections, particularly in patients with **diabetes** or profound immunosuppression. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as small, **oval yeasts** within macrophages in tissue samples, rather than septate hyphae outside of macrophages. - It causes **histoplasmosis**, an endemic fungal infection associated with exposure to **bird or bat droppings**, and can lead to pulmonary disease, especially in immunocompromised patients. *Candida albicans* - *Candida albicans* typically appears as **budding yeasts** and **pseudohyphae** (elongated yeast cells that resemble hyphae but are constricted at the septa) on microscopy. True septate hyphae with acute angle branching are not its characteristic morphology in tissue. - While *Candida* can cause pulmonary infections in severely immunocompromised patients, it more commonly causes **mucosal infections** (e.g., thrush, esophagitis) or **candidemia**.

Question 493: Which combination of staining methods is best for visualizing the capsule of Cryptococcus neoformans in cerebrospinal fluid (CSF)?

A. Gram stain and Giemsa stain
B. Leishman stain and Gram stain
C. Giemsa stain and Ponder's stain
D. India ink preparation and Mucicarmine stain (Correct Answer)

Explanation: ***India ink preparation and Mucicarmine stain*** - **India ink preparation** is ideal for visualizing the **capsule** of *Cryptococcus neoformans* as it stains the background dark, making the clear halo of the capsule visible around the yeast cells. - **Mucicarmine stain** specifically highlights the **polysaccharide capsule** of *Cryptococcus* in red or pink, confirming its presence and aiding in differentiation. *Gram stain and Giemsa stain* - **Gram stain** is used to classify bacteria based on their cell wall, but it stains *Cryptococcus* as **Gram-positive** and does not effectively visualize the capsule. - **Giemsa stain** is used for blood parasites and intracellular structures but is not specific or effective for demonstrating the *Cryptococcus* capsule. *Leishman stain and Gram stain* - **Leishman stain** is primarily used for blood and bone marrow smears to visualize cells and parasites, offering no specific advantage for *Cryptococcus* capsule visualization. - **Gram stain**, as mentioned, stains fungal cells but does not provide clear capsular visualization. *Giemsa stain and Ponder's stain* - **Giemsa stain** is not optimal for visualizing the *Cryptococcus* capsule. - **Ponder's stain** (or Albert's stain) is primarily used for demonstrating metachromatic granules in *Corynebacterium diphtheriae* and is not useful for fungal capsules.

Question 494: A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?

A. Aspergillus fumigatus
B. Rhizopus spp. (Correct Answer)
C. Candida albicans
D. Cryptococcus neoformans

Explanation: ***Rhizopus spp.*** - The patient's presentation with **sinus pain**, **nasal discharge**, **facial swelling**, and a history of **poorly controlled diabetes** is classic for **mucormycosis** (also known as zygomycosis). - **Biopsy findings** of **broad, nonseptate hyphae branching at wide/irregular angles** are pathognomonic for mucormycosis, most commonly caused by *Rhizopus* species. - Diabetes mellitus, particularly when poorly controlled with **ketoacidosis**, is a major risk factor for rhinocerebral mucormycosis. *Aspergillus fumigatus* - This fungus typically causes infections with **septate hyphae** that **branch at acute angles** (45 degrees), which is morphologically distinct from mucormycosis. - While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, the specific hyphal morphology (nonseptate, wide-angle branching) points away from it. *Candida albicans* - *Candida albicans* is a yeast that typically appears as **oval budding cells** and **pseudohyphae** on microscopy, not broad, nonseptate hyphae. - While it can cause opportunistic infections in diabetic and immunocompromised patients, its microscopic appearance is entirely inconsistent with the biopsy findings. *Cryptococcus neoformans* - *Cryptococcus neoformans* is an **encapsulated yeast** that is typically identified by its **spherical or oval budding cells** with a characteristic **polysaccharide capsule** visible with India ink stain. - It primarily causes **meningitis** and pulmonary infections in immunocompromised hosts, and its morphology (yeast, not hyphae) is entirely different from the described findings.

Question 495: A 50-year-old farmer with diabetes presents with a chronic ulcer on his foot that has not healed despite standard wound care. A biopsy reveals fungal elements, and the culture grows a mold with septate hyphae and green conidia. What is the likely causative organism?

A. Candida albicans
B. Aspergillus fumigatus (Correct Answer)
C. Rhizopus oryzae
D. Histoplasma capsulatum

Explanation: **Aspergillus fumigatus** - The presence of **septate hyphae** and **green conidia** on culture is characteristic of *Aspergillus* species, particularly *Aspergillus fumigatus*. - Patients with **diabetes** are at a higher risk for fungal infections, and chronic non-healing ulcers can be a presentation of localized **aspergillosis**. *Candida albicans* - *Candida albicans* typically presents as **yeast** and **pseudohyphae** on microscopy, not septate hyphae with green conidia. - While it can cause chronic ulcers, its microscopic morphology and culture characteristics differ significantly from the description. *Rhizopus oryzae* - *Rhizopus oryzae* is a **mucormycete** characterized by **broad, aseptate hyphae** with right-angle branching, which contrasts with the septate hyphae described. - It causes mucormycosis, a severe infection often involving the rhinocerebral area, though cutaneous forms can occur. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as small, oval budding yeasts within macrophages in tissue. - It is typically associated with pulmonary infections and disseminated disease, not chronic foot ulcers with septate hyphae and green conidia on culture.

Question 496: A patient with AIDS presents with meningitis. An India ink preparation of the cerebrospinal fluid shows encapsulated yeast cells. Which organism is most likely responsible?

A. Candida albicans
B. Cryptococcus neoformans (Correct Answer)
C. Histoplasma capsulatum
D. Coccidioides immitis

Explanation: ***Cryptococcus neoformans*** - This organism is a **common cause of meningitis in AIDS patients** due to their severely compromised immune systems (low CD4 counts). - The presence of **encapsulated yeast cells** visible on an **India ink preparation of CSF** is pathognomonic for *Cryptococcus neoformans*. - The **India ink negative staining technique** highlights the thick polysaccharide capsule, which appears as a clear halo around the yeast cells against a dark background. *Candida albicans* - While *Candida albicans* can cause various infections in immunocompromised individuals, **Candidal meningitis is rare** and would not typically show encapsulated yeast on India ink. - *Candida* usually presents as **pseudohyphae and budding yeasts** and is not primarily identified by India ink preparations for capsules in CSF. *Histoplasma capsulatum* - *Histoplasma capsulatum* can cause **disseminated histoplasmosis**, including central nervous system involvement, especially in AIDS patients. - However, it is an **intracellular dimorphic fungus** and does not typically present as encapsulated yeast in the CSF on India ink stain. *Coccidioides immitis* - *Coccidioides immitis* can cause **Coccidioidal meningitis**, particularly in endemic areas and immunocompromised patients. - It is characterized by **spherules containing endospores** in tissue and CSF, not encapsulated yeast cells.

Question 497: Which of the following fungi is classified as lipophilic?

A. Malassezia furfur (Correct Answer)
B. Candida
C. Cryptococcus
D. Histoplasma

Explanation: ***Malassezia furfur*** - **Malassezia furfur** is a genus of fungi that is **lipophilic**, meaning it requires **lipids for growth** and must be cultured on **media supplemented with olive oil or long-chain fatty acids**. - It causes conditions like **pityriasis versicolor** and **seborrheic dermatitis**, thriving in oily skin areas. - This is the classic example of a lipid-dependent fungus in medical microbiology. *Candida* - **Candida** is a genus of yeast that is **not lipophilic**; it grows well on various sugar-containing media like Sabouraud dextrose agar. - It is a common cause of **mucocutaneous infections** like thrush and candidiasis, and opportunistic systemic infections. *Cryptococcus* - **Cryptococcus** is a yeast known for causing **meningitis** and pulmonary infections, especially in immunocompromised individuals. - It is **not lipophilic** and typically grows on media designed for general fungal growth. *Histoplasma* - **Histoplasma capsulatum** is a dimorphic fungus that causes **histoplasmosis**, primarily affecting the lungs. - It is **not lipophilic** and grows in soil enriched with bird or bat droppings.

Question 498: Chlamydospore is formed by ?

A. Candida tropicalis
B. Histoplasma
C. Candida albicans (Correct Answer)
D. Cryptococcus

Explanation: ***Candida albicans*** - *Candida albicans* is distinguished by its ability to form **chlamydospores** when cultured under specific conditions, which is an important diagnostic feature. - These are thick-walled, spherical spores, often found terminally or intercalary, that aid in its identification in the laboratory. *Candida tropicalis* - While *Candida tropicalis* is another clinically significant *Candida* species, it typically does not produce **chlamydospores**. - Its identification relies on other biochemical tests and macroscopic/microscopic morphological characteristics like **pseudohyphae** and **blastoconidia**. *Histoplasma* - *Histoplasma capsulatum* is a **dimorphic fungus** known for causing **histoplasmosis**, and its morphology includes **tuberculate macroconidia** and microconidia, not chlamydospores. - It exists as a mold in the environment and a yeast in human tissues. *Cryptococcus* - *Cryptococcus neoformans* is an **encapsulated yeast** primarily identified by its prominent **polysaccharide capsule** and urease production. - It is known for causing **cryptococcosis**, especially in immunocompromised individuals, and does not form chlamydospores.

Question 499: Which of the following fungi is MOST characteristically associated with meningitis in immunocompromised patients?

A. Histoplasma capsulatum
B. Cryptococcus neoformans (Correct Answer)
C. Candida albicans
D. Trichophyton

Explanation: ***Cryptococcus neoformans*** - This encapsulated yeast is the most common cause of **fungal meningitis**, especially in **immunocompromised individuals**, such as those with HIV/AIDS or organ transplant recipients. - Infection typically occurs through inhalation of spores, leading to pulmonary involvement that can disseminate to the central nervous system. *Histoplasma capsulatum* - While it can cause disseminated disease in immunocompromised patients, including central nervous system (CNS) involvement, it is more commonly associated with **pulmonary histoplasmosis** and less frequently the primary cause of meningitis compared to **Cryptococcus**. - Its geographical distribution is limited to areas with high concentrations of **bird or bat droppings**. *Trichophyton* - **Trichophyton species** are **dermatophytes** that primarily cause **superficial fungal infections** of the skin, hair, and nails (e.g., ringworm, athlete's foot). - They are not a known cause of **meningitis** or **invasive systemic infections**. *Candida albicans* - **Candida albicans** can cause **invasive candidiasis**, including CNS infections, particularly in critically ill or severely immunocompromised patients. - However, **Candida meningitis** is less common and typically occurs in specific high-risk settings (e.g., following neurosurgery or in very premature infants) compared to **Cryptococcus meningitis** in the broader immunocompromised population.

Question 500: Which organism is associated with a positive hair perforation test?

A. Trichophyton (Correct Answer)
B. None of the options
C. Microsporum
D. Epidermophyton

Explanation: ***Correct Option: Trichophyton*** - The **hair perforation test** is used to identify dermatophytes that can produce **wedge-shaped perforations** in sterilized hair shafts *in vitro* - **Trichophyton mentagrophytes** and related species (like *T. mentagrophytes var. mentagrophytes*) are classically **positive** for this test - This test helps distinguish between: - **Positive species:** *T. mentagrophytes* (causes perforations) - **Negative species:** *T. rubrum* (does not perforate hair) - The test involves incubating dermatophytes with sterilized blonde human hair in sterile water for 2-4 weeks and examining for characteristic perforations under microscopy - Among dermatophyte genera, **Trichophyton** is the primary genus associated with positive hair perforation tests in clinical microbiology *Incorrect Option: Microsporum* - *Microsporum* species cause **ectothrix** hair invasion patterns in vivo but generally do **not produce positive hair perforations** in the standardized *in vitro* test - *Microsporum canis* and other species in this genus typically yield negative results *Incorrect Option: Epidermophyton* - *Epidermophyton floccosum* is the only medically significant species in this genus - It causes **skin and nail infections** (tinea corporis, cruris, pedis) but does **not infect hair** - Therefore, it cannot produce positive hair perforation test results *Incorrect Option: None of the options* - This is incorrect because **Trichophyton** (specifically *T. mentagrophytes*) is the standard correct answer for organisms showing positive hair perforation tests in medical microbiology

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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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