Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 241: Which stains are commonly used in the study of fungal infections?

A. Gomori methanamine silver
B. PAS
C. H & E
D. All the above (Correct Answer)

Explanation: **Explanation:** In medical mycology, the visualization of fungal elements in tissue sections is crucial for diagnosis. While different stains have varying levels of sensitivity and specificity, all the options listed are utilized in clinical practice. * **Gomori Methenamine Silver (GMS):** This is considered the **gold standard** for fungal staining. It utilizes silver ions that bind to the carbohydrates (polysaccharides) in the fungal cell wall, staining them black or dark brown against a green background. It is highly sensitive and can detect even non-viable fungi. * **Periodic Acid-Schiff (PAS):** This stain reacts with the polysaccharides (chitin and glucan) in the fungal cell wall. Fungal elements appear **bright magenta/pink**. It provides better morphological detail of the host tissue compared to GMS. * **Hematoxylin and Eosin (H&E):** Although H&E is a general-purpose tissue stain, it is often the first slide reviewed. While many fungi are pale or difficult to see, some (like *Aspergillus* or *Mucor*) can be visualized. Importantly, H&E is essential to identify the **host’s inflammatory response** (e.g., granulomas) and the natural pigment of **dematiaceous (pigmented) fungi**. **Conclusion:** Since all three stains are routinely employed to identify fungi or the tissue reaction they cause, "All the above" is the correct choice. **High-Yield Clinical Pearls for NEET-PG:** * **Mucicarmine Stain:** Specific for *Cryptococcus neoformans* (stains the polysaccharide capsule red). * **India Ink:** Used for rapid identification of *Cryptococcus* in CSF (negative staining). * **Calcofluor White:** A fluorescent stain that binds to chitin; requires a fluorescent microscope. * **Masson-Fontana:** Used to detect melanin in the cell walls of dematiaceous fungi.

Question 242: Which of the following is a capsulated fungus?

A. Histoplasma capsulatum
B. Cladophialophora
C. Cryptococcus (Correct Answer)
D. Alternaria

Explanation: **Explanation:** The presence of a polysaccharide capsule is a defining virulence factor for **Cryptococcus neoformans** and **Cryptococcus gattii** [1]. This capsule is composed primarily of glucuronoxylomannan (GXM) [2], which inhibits phagocytosis and allows the fungus to evade the host immune system. In clinical practice, this capsule is classically demonstrated using **India Ink preparation**, where it appears as a clear halo against a dark background, or via the **Mucicarmine stain**, which stains the capsule bright red. **Analysis of Incorrect Options:** * **Histoplasma capsulatum (Option A):** Despite its misleading name, *Histoplasma* is **not** capsulated. The name was given by its discoverer, Samuel Darling, who mistook the halo seen around the yeast cells in tissue sections (a shrinkage artifact) for a capsule. * **Cladophialophora (Option B):** This is a genus of dematiaceous (pigmented) fungi responsible for Chromoblastomycosis. It is characterized by melanin in the cell wall, not a capsule. * **Alternaria (Option C):** This is a common environmental mold and an opportunistic pathogen. It is non-capsulated and characterized by multicellular, "club-shaped" macroconidia with transverse and longitudinal septations. **High-Yield Facts for NEET-PG:** * **Cryptococcus** is the only medically important fungus with a prominent polysaccharide capsule [1]. * **Diagnosis:** The **CrAg (Cryptococcal Antigen)** test (Latex agglutination or LFA) is the most sensitive and specific method for detection in CSF and serum [3]. * **Culture:** It grows on Sabouraud Dextrose Agar (SDA) as creamy, mucoid colonies. It is **urease positive**. * **Clinical Association:** It is the most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100 cells/µL) [4].

Question 243: Darling disease is caused by which organism?

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

Explanation: **Explanation:** **Histoplasma capsulatum** is the causative agent of **Darling’s disease** (also known as Histoplasmosis or Cave disease). It is a dimorphic fungus that exists as a mold in the environment (soil enriched with bird or bat droppings) and as an intracellular yeast within macrophages in the human body. The name "Darling’s disease" honors Samuel Taylor Darling, who first described the organism in 1905. **Analysis of Options:** * **Histoplasma (Correct):** It is a systemic mycosis primarily affecting the lungs. It is endemic in the Ohio and Mississippi River valleys. * **Candida:** Causes opportunistic infections ranging from oral thrush and vaginal candidiasis to systemic candidemia. It is not associated with Darling’s disease. * **Cryptococcus:** An encapsulated yeast (C. neoformans) typically causing meningitis in immunocompromised patients. It is often associated with pigeon droppings but is not the cause of Darling’s disease. * **Rhizopus:** A member of the Mucormycetes family causing Mucormycosis (Zygomycosis), characterized by broad, non-septate hyphae with right-angled branching. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Histoplasma is the only fungus that is **obligate intracellular** (found inside macrophages). * **Diagnosis:** On peripheral smear or biopsy, look for small, oval yeast cells with a "halo" (though they lack a true capsule). * **Transmission:** Inhalation of spores from soil contaminated with **bat guano** (spelunkers/cave explorers) or bird droppings. * **Clinical Mimicry:** Chronic histoplasmosis often mimics **Tuberculosis** (granulomas and calcifications on CXR). * **Treatment:** Itraconazole for mild cases; Amphotericin B for severe/disseminated disease.

Question 244: Which of the following statements is TRUE about Histoplasmosis?

A. In early stages, it is indistinguishable from tuberculosis. (Correct Answer)
B. Culture is diagnostic.
C. Hyphal forms are the infectious form.
D. Person-to-person spread occurs by droplet infection.

Explanation: **Histoplasmosis** is a systemic fungal infection caused by the dimorphic fungus *Histoplasma capsulatum*. It is a high-yield topic for NEET-PG due to its clinical similarity to tuberculosis. ### **Explanation of the Correct Option** **Option A is correct.** In early stages, pulmonary histoplasmosis is **clinically and radiologically indistinguishable from Tuberculosis (TB)**. Both present with fever, cough, weight loss, and night sweats. Radiologically, both can show hilar lymphadenopathy, pulmonary infiltrates, and even granuloma formation. In endemic areas, histoplasmosis is a major differential diagnosis for "culture-negative TB." ### **Why Other Options are Incorrect** * **Option B:** While culture is the "gold standard," it is **not the primary diagnostic tool** in clinical practice because *Histoplasma* is slow-growing (taking 2–6 weeks). Diagnosis is more commonly reached via **histopathology** (showing intracellular yeast in macrophages) or **urinary antigen detection**, which is faster and highly sensitive. * **Option C:** The **microconidia** (spores) are the infectious form, not the hyphae themselves. These spores are inhaled from soil enriched with bird or bat droppings. * **Option D:** There is **no person-to-person transmission**. Infection occurs solely through the inhalation of environmental spores. ### **High-Yield Clinical Pearls for NEET-PG** * **Morphology:** It is a **dimorphic fungus**. At 37°C (in the body), it exists as **small intracellular yeasts** within macrophages (look for "narrow-based budding"). At 25°C (culture), it shows **tuberculate macroconidia**. * **Habitat:** Associated with **soil contaminated by bat guano** (caves) or bird droppings (chicken coops). * **Pathology:** It is the only fungus that is an **obligate intracellular parasite** of the reticuloendothelial system. * **Treatment:** Mild cases are self-limiting; moderate-to-severe cases require **Itraconazole**, while disseminated disease requires **Amphotericin B**.

Question 245: Which fungal infection is known as Gilchrist's disease?

A. Coccidiomycosis
B. Paracoccidiomycosis
C. Sporotrichosis
D. Blastomycosis (Correct Answer)

Explanation: **Explanation:** **Blastomycosis** (Option D) is caused by the dimorphic fungus *Blastomyces dermatitidis*. It is eponymously known as **Gilchrist's disease**, named after Thomas Caspar Gilchrist, who first described the organism in 1894. The infection is typically acquired through inhalation of spores from soil or decomposing wood, primarily in the Great Lakes and Mississippi River Valley regions. **Analysis of Options:** * **A. Coccidiomycosis:** Also known as **Valley Fever** or San Joaquin Valley Fever. It is characterized by spherules containing endospores in tissue. * **B. Paracoccidiomycosis:** Also known as **South American Blastomycosis** or Lutz-Splendore-Almeida disease. It is famous for the "Pilot’s wheel" or "Mickey Mouse" appearance of yeast cells. * **C. Sporotrichosis:** Commonly known as **Rose Gardener’s disease**. It typically presents with lymphocutaneous spread following traumatic inoculation (e.g., thorn pricks). **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** *Blastomyces* is characterized by **Broad-Based Budding** yeast cells (the "B"s: Blastomyces, Broad-based, Big). * **Dimorphism:** It exists as mold in the environment ($25^\circ\text{C}$) and as yeast in human tissue ($37^\circ\text{C}$). * **Clinical Presentation:** Can manifest as pulmonary infection or disseminated disease, frequently involving the **skin** (verrucous lesions) and **bones**. * **Drug of Choice:** Itraconazole for mild-to-moderate disease; Amphotericin B for severe or systemic infections.

Question 246: A diabetic patient presents with a black necrotic mass filling the nasal cavity. What is the most likely fungal infection?

A. Rhinosporidiosis
B. Aspergillosis
C. Mucormycosis (Correct Answer)
D. Candidiasis

Explanation: ### Explanation **Correct Answer: C. Mucormycosis** **Why it is correct:** The clinical presentation of a **diabetic patient** (especially one in ketoacidosis) with a **black necrotic mass** (eschar) in the nasal cavity is a classic hallmark of **Rhinocerebral Mucormycosis**. The underlying medical concept is **angioinvasion**: the fungi (genera *Rhizopus*, *Mucor*, and *Lichtheimia*) invade blood vessel walls, leading to thrombosis and subsequent tissue infarction/necrosis. This necrosis manifests as the characteristic black eschar. High glucose levels and acidic pH (in DKA) provide an ideal environment for these fungi to thrive by increasing free iron availability. **Why the other options are incorrect:** * **Rhinosporidiosis (A):** Caused by *Rhinosporidium seeberi*, it typically presents as a friable, leafy, strawberry-like polypoid mass in the nose, usually following exposure to stagnant water. It does not cause black necrosis. * **Aspergillosis (B):** While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, it is less specifically associated with diabetic ketoacidosis and is not the "classic" cause of the rapid, black necrotic eschar described in board exams. * **Candidiasis (D):** *Candida* typically causes mucosal surfaces to show white patches (thrush) or pseudomembranes. It does not typically present as an invasive, necrotic nasal mass. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Look for **broad, aseptate hyphae** branching at **right angles (90°)**. * **Risk Factors:** Uncontrolled Diabetes (DKA), Neutropenia, and Iron overload (Deferoxamine use). * **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as "cotton candy" colonies.

Question 247: What is the term for a fungal infection of humans?

A. Mucormycosis
B. Mycosis (Correct Answer)
C. Fungosis
D. Micromia

Explanation: **Explanation:** **Correct Answer: B. Mycosis** In medical terminology, the suffix **"-osis"** denotes a condition, disease, or process, while the prefix **"myco-"** (derived from the Greek *mykes*) refers to fungi. Therefore, **Mycosis** is the universal medical term used to describe any disease caused by a fungus invading human or animal tissue. Mycoses are clinically categorized based on the site of infection into superficial, cutaneous, subcutaneous, systemic (deep), and opportunistic infections. **Analysis of Incorrect Options:** * **A. Mucormycosis:** This is a specific, aggressive type of opportunistic mycosis caused by fungi in the order *Mucorales* (e.g., *Rhizopus*, *Mucor*). While it is a fungal infection, it is a specific diagnosis rather than the general term for all fungal diseases. * **C. Fungosis:** This is a common distractor. Although "fungus" is the causative agent, "fungosis" is not a standard medical term used in clinical microbiology. * **D. Micromia:** This is a fabricated term with no relevance to mycology. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Remember the distinction between **Primary Pathogens** (e.g., *Histoplasma*) which can infect healthy hosts, and **Opportunistic Pathogens** (e.g., *Candida*, *Aspergillus*) which primarily affect immunocompromised individuals. * **Dimorphic Fungi:** A favorite topic for NEET-PG. These fungi exist as **molds** (at 25°C/ambient temperature) and **yeasts** (at 37°C/body temperature). *Mnemonic: "Mold in the Cold, Yeast in the Beast."* * **Diagnosis:** The gold standard for initial microscopic visualization of fungi in clinical samples is the **KOH (Potassium Hydroxide) mount**, which dissolves keratin to reveal fungal elements.

Question 248: What is a tangled mass of hyphae called?

A. Conidia
B. Molds
C. Pseudopodia
D. Mycelium (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Mycelium** In medical mycology, fungi are classified based on their morphology. **Hyphae** are the fundamental branching, thread-like tubular structures of filamentous fungi. When these hyphae grow, branch, and intertwine to form a visible, tangled mass or "mat," the entire structure is referred to as a **Mycelium**. Mycelium can be *vegetative* (burrowing into the medium for nutrients) or *aerial* (projecting above the surface, often bearing spores). **Analysis of Incorrect Options:** * **A. Conidia:** These are asexual, non-motile spores formed at the tip or side of specialized hyphae (conidiophores). They are units of reproduction, not the mass of the fungus itself. * **B. Molds:** This is a general term for multicellular, filamentous fungi. While molds *consist* of mycelia, the specific anatomical term for the "tangled mass of hyphae" is mycelium. * **C. Pseudopodia:** These are "false feet" or temporary cytoplasmic protrusions used for locomotion and feeding by amoeboid protozoa (e.g., *Entamoeba histolytica*), not fungi. **High-Yield Clinical Pearls for NEET-PG:** 1. **Septate vs. Aseptate:** Fungi like *Aspergillus* have septate hyphae (divided by cross-walls), whereas Zygomycetes (e.g., *Rhizopus*, *Mucor*) have coenocytic/aseptate hyphae. 2. **Pseudohyphae:** Characteristic of *Candida albicans*, these are formed by incomplete budding where cells remain attached, showing constricted septations (unlike true hyphae which have parallel walls). 3. **Dimorphic Fungi:** These exist as molds (mycelial form) in the environment/culture at 25°C and as yeasts in host tissues at 37°C (Mnemonic: *Mold in the Cold, Yeast in the Heat*).

Question 249: What is the causative organism of boggy swelling of hair?

A. Trichophyton mentagrophytes (Correct Answer)
B. E. flocosum
C. M. canis
D. T. concentricum

Explanation: **Explanation:** The clinical presentation of a "boggy swelling" of the scalp is known as a **Kerion**. This is an inflammatory, painful, and crusting lesion of the scalp (Tinea capitis) that often leads to scarring alopecia. 1. **Why Trichophyton mentagrophytes is correct:** Kerion is typically caused by **zoophilic** (animal-to-human) or **geophilic** (soil-to-human) dermatophytes. *Trichophyton mentagrophytes* (specifically the *mentagrophytes* variety) is a common zoophilic organism that triggers a vigorous cell-mediated immune response in the host, leading to the characteristic inflammatory boggy swelling. 2. **Why the other options are incorrect:** * **E. floccosum:** This is an anthropophilic fungus that primarily affects the skin (Tinea cruris/pedis) and nails. Crucially, *Epidermophyton* species **never** infect hair. * **M. canis:** While *Microsporum canis* is zoophilic and can cause Tinea capitis, it typically presents as "Gray Patch" (non-inflammatory) or mildly inflammatory lesions. It is less commonly associated with the severe, suppurative Kerion compared to *T. mentagrophytes* or *T. verrucosum*. * **T. concentricum:** This organism is the causative agent of **Tinea imbricata**, characterized by distinctive concentric rings of scales. It does not typically cause boggy scalp swellings. **NEET-PG Clinical Pearls:** * **Kerion:** Inflammatory Tinea capitis; most common causes are *T. verrucosum* (cattle) and *T. mentagrophytes* (rodents). * **Favus:** Characterized by **scutula** (cup-shaped crusts) and mousy odor, caused by *T. schoenleinii*. * **Wood’s Lamp:** *Microsporum* species show bright green fluorescence; *Trichophyton* species (except *T. schoenleinii*) generally do not fluoresce. * **Treatment:** Oral Griseofulvin is the traditional gold standard for Tinea capitis.

Question 250: Candida albicans can be differentiated from other Candida species on cornmeal agar by its unique ability to form which of the following?

A. Aseptate hyphae
B. Germ tubes
C. Chlamydospores (Correct Answer)
D. Arthrospores

Explanation: ### Explanation **Correct Option: C. Chlamydospores** *Candida albicans* is uniquely identified on **Cornmeal Agar (CMA)** by the production of **thick-walled, terminal resting spores called Chlamydospores**. CMA is a nutritionally deficient medium that induces stress in the fungus, stimulating the formation of these characteristic structures. This is a definitive morphological test used in laboratories to differentiate *C. albicans* (and the closely related *C. dubliniensis*) from other non-albicans species. **Analysis of Incorrect Options:** * **A. Aseptate hyphae:** These are characteristic of Zygomycetes (e.g., *Rhizopus*, *Mucor*). *Candida* species are yeasts that produce septate pseudohyphae and true hyphae. * **B. Germ tubes:** While the **Germ Tube Test (Reynolds-Braude phenomenon)** is a rapid diagnostic test for *C. albicans*, it is performed using **human or rabbit serum** incubated at 37°C for 2–3 hours, not on cornmeal agar. * **D. Arthrospores:** These are formed by the fragmentation of hyphae and are characteristic of fungi like *Trichosporon* and *Geotrichum candidum*, but not *Candida*. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** The earliest morphological change in *C. albicans* when shifted from 25°C to 37°C in serum. * **Phenotypic Switching:** *C. albicans* can switch between yeast (commensal) and hyphal (pathogenic/invasive) forms. * **C. dubliniensis:** The only other species that produces chlamydospores and is germ tube positive; it is typically differentiated by its inability to grow at 45°C. * **CHROMagar:** A specialized differential medium where *C. albicans* produces characteristic **light green** colonies.

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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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