Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 211: Tinea Nigra is caused by which organism?

A. Hortaea werneckii (Correct Answer)
B. Piedrae hortae
C. T. rubrum
D. Microsporum

Explanation: **Explanation:** **Tinea Nigra** is a superficial fungal infection (superficial mycosis) characterized by asymptomatic, brown-to-black non-scaly macules, typically on the palms and soles. 1. **Why Option A is Correct:** The causative agent of Tinea Nigra is **Hortaea werneckii** (formerly known as *Exophiala werneckii*). It is a **dematiaceous** (pigmented) fungus that produces melanin, giving the clinical lesion its characteristic dark appearance. Diagnosis is confirmed by skin scrapings in KOH, which show branched, septate dark hyphae and elongated budding cells. 2. **Why Other Options are Incorrect:** * **B. Piedraia hortae:** This organism causes **Black Piedra**, a superficial infection of the hair shaft characterized by hard, black nodules. * **C. T. rubrum (Trichophyton rubrum):** This is a dermatophyte and the most common cause of Tinea corporis, Tinea pedis, and Onychomycosis. It involves deeper keratinized layers compared to Tinea Nigra. * **D. Microsporum:** This is a genus of dermatophytes that commonly causes Tinea capitis and Tinea corporis, often characterized by ectothrix hair involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Often misdiagnosed as malignant melanoma; however, Tinea Nigra is superficial and can be "scraped off." * **Transmission:** Usually occurs via traumatic inoculation from soil, sewage, or decaying vegetation. * **Culture:** On Sabouraud Dextrose Agar (SDA), it produces black, mucoid, yeast-like colonies. * **Treatment:** Topical antifungal creams (e.g., Whitfield ointment, imidazoles).

Question 212: Which of the following is true about Rhinosporidium Seeberi?

A. It is a fungus.
B. It is a bacterium. (Correct Answer)
C. It is treated with Ketoconazole.
D. All of the above.

Explanation: **Explanation:** *Rhinosporidium seeberi* has long been a subject of taxonomic debate. While traditionally classified as a fungus due to its morphology (producing sporangia and spores), modern molecular analysis (18S rRNA sequencing) has reclassified it. **1. Why the correct answer is "It is a bacterium" (Contextual Note):** In the context of recent taxonomic shifts, *Rhinosporidium seeberi* is now classified as a **Mesomycetozoean**, a group of fish parasites located at the evolutionary boundary between animals and fungi. However, in many older medical curricula and specific competitive exam keys, it was historically distinguished from "true fungi." While technically a protist, it is definitely **not** a fungus. (Note: If "Protist" is not an option, it is often grouped with aquatic parasites). **2. Why the other options are incorrect:** * **Option A (It is a fungus):** Molecular phylogeny has proven it lacks chitin in its cell wall and does not grow on fungal media (SDA). It belongs to the class *Mesomycetozoea*. * **Option C (Treated with Ketoconazole):** Since it is not a fungus, conventional antifungals like Ketoconazole are ineffective. The treatment of choice is **Surgical Excision** with electrocautery of the base. **Dapsone** is the only medical therapy shown to prevent recurrence by inhibiting spore maturation. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by **friable, leafy, strawberry-like polypoid masses** in the nose (most common), nasopharynx, or conjunctiva. * **Transmission:** Associated with bathing in stagnant freshwater/ponds. * **Diagnosis:** Cannot be cultured. Diagnosis is via histopathology showing **large thick-walled sporangia** (up to 350 µm) containing thousands of **endospores**. * **Staining:** Sporangia stain well with GMS, PAS, and Mucicarmine.

Question 213: Impaired immune competence is the predisposing factor in about half of all persons who develop which of the following fungal infections?

A. Histoplasmosis
B. Coccidoidomycosis
C. Blastomycosis
D. Cryptococcosis (Correct Answer)

Explanation: **Explanation:** The correct answer is **Cryptococcosis**. **1. Why Cryptococcosis is correct:** *Cryptococcus neoformans* is considered a classic **opportunistic fungal pathogen**. While it can occasionally infect healthy individuals, approximately **50% to 80%** of clinically significant cases occur in patients with impaired cell-mediated immunity (CMI). The most common predisposing factor is HIV/AIDS (typically when CD4 counts are <100 cells/µL), followed by organ transplant recipients, patients on chronic corticosteroids, and those with hematological malignancies. The fungus is inhaled but requires a weakened immune system to disseminate, most commonly causing meningoencephalitis. **2. Why the other options are incorrect:** * **A, B, and C (Histoplasmosis, Coccidioidomycosis, and Blastomycosis):** These are classified as **Systemic (Endemic) Mycoses**. Unlike opportunistic fungi, these are **primary pathogens**, meaning they are inherently virulent and can cause significant disease in **immunocompetent** individuals who inhale a sufficient fungal load. While immunosuppression can lead to more severe or disseminated forms of these diseases, the majority of infections occur in healthy hosts living in endemic geographical regions. **3. NEET-PG High-Yield Pearls:** * **Source:** Pigeon droppings and contaminated soil. * **Virulence Factor:** The **Polysaccharide capsule** (inhibits phagocytosis) is the most important. * **Diagnosis:** * **India Ink:** Shows a clear halo (capsule) against a dark background. * **Culture:** Niger seed agar/Bird seed agar (produces melanin). * **Antigen Detection:** CrAg (Cryptococcal Antigen) via Lateral Flow Assay is the most sensitive screening test. * **Histopathology:** Mucicarmine stain (stains capsule red). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Question 214: Which fungus is capable of forming a fungal ball?

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

Explanation: **Explanation:** **Aspergillus** is the most common cause of a **fungal ball (Aspergilloma)**. This occurs when the fungus colonizes a pre-existing lung cavity (most commonly formed by **Tuberculosis**, but also sarcoidosis or bronchiectasis). The fungus grows as a saprophytic mass of hyphae, fibrin, and cellular debris without invading the surrounding tissue. On a chest X-ray, it presents as a mobile, gravity-dependent mass with a characteristic **"Air-crescent sign" (Monod sign)**. **Analysis of Options:** * **Aspergillus (Correct):** Specifically *Aspergillus fumigatus*. It is unique in its ability to form non-invasive balls in pulmonary cavities. * **Mucor & Rhizopus (Incorrect):** These belong to the order Mucorales. They are characterized by **angioinvasion**, leading to infarction and necrosis (e.g., Rhinocerebral mucormycosis). They do not typically form organized, non-invasive fungal balls. * **Penicillium (Incorrect):** While *Talaromyces (Penicillium) marneffei* is a significant pathogen in HIV patients, it causes disseminated intracellular infection rather than cavitary fungal balls. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** Gold standard is culture; however, the presence of **serum precipitins (IgG antibodies)** against Aspergillus is highly sensitive for Aspergilloma. 2. **Microscopy:** Aspergillus shows **septate hyphae** with **acute-angle (45°) branching**, whereas Mucorales show broad, aseptate hyphae with right-angle branching. 3. **Clinical Presentation:** The most common symptom of an Aspergilloma is **hemoptysis**, which can occasionally be life-threatening. 4. **Treatment:** Surgical resection is the definitive treatment for symptomatic cases; systemic antifungals have poor penetration into the fungal ball.

Question 215: Systemic infection is caused by all fungi except?

A. Cryptococcus
B. Histoplasma
C. Dermatophytes (Correct Answer)
D. Paracoccidioides

Explanation: **Explanation:** The classification of fungal infections is based on the depth of tissue involvement. Fungi are categorized into superficial, cutaneous, subcutaneous, and systemic (deep) mycoses. **Why Dermatophytes is the correct answer:** Dermatophytes (genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*) cause **cutaneous mycoses**. These fungi are "keratinophilic," meaning they require keratin for growth. Since keratin is only found in the non-living cornified layers of the skin, hair, and nails, these infections remain restricted to the **superficial integument**. They lack the biochemical machinery to invade deeper tissues or survive at core body temperatures, thus they **do not cause systemic infection.** **Analysis of Incorrect Options:** * **Cryptococcus:** An encapsulated yeast (primarily *C. neoformans*) that causes systemic disease, most notably meningitis and pulmonary infections, especially in immunocompromised patients. * **Histoplasma:** A dimorphic fungus that causes systemic histoplasmosis. It is an intracellular pathogen that involves the reticuloendothelial system (lungs, liver, spleen). * **Paracoccidioides:** A dimorphic fungus causing Paracoccidioidomycosis, a systemic infection prevalent in South America that affects the lungs and mucous membranes. **NEET-PG High-Yield Pearls:** * **Systemic Mycoses** are typically caused by dimorphic fungi (except *Cryptococcus*, which is a yeast). * **Dermatophytes** are diagnosed using KOH mounts showing branching hyphae and are treated with topical antifungals or oral Griseofulvin/Terbinafine. * **Wood’s Lamp:** Used to detect certain *Microsporum* species (fluoresce bright green). * **Culture Media:** Sabouraud Dextrose Agar (SDA) is the standard medium for most fungi.

Question 216: Draining sinuses are seen in which of the following conditions?

A. Mycetoma (Correct Answer)
B. Scrofula
C. Lupus vulgaris
D. Pediculosis

Explanation: **Explanation:** **Mycetoma** is a chronic, granulomatous infection of the skin and subcutaneous tissue, most commonly affecting the foot (Madura foot). The classic clinical triad of Mycetoma consists of: 1. **Localized swelling** (Tumefaction) 2. **Multiple interconnecting draining sinuses** 3. **Presence of grains** (sulfur-like granules) in the discharge. It is caused by either fungi (**Eumycetoma**) or filamentous bacteria (**Actinomycetoma**). The sinuses serve as channels for the body to discharge these colonial grains. **Analysis of Incorrect Options:** * **Scrofula:** This is tuberculous cervical lymphadenitis. While it can lead to "cold abscesses" that may eventually rupture to form sinuses, it is primarily a lymph node pathology rather than a primary subcutaneous infection characterized by the classic draining sinus triad. * **Lupus Vulgaris:** A progressive form of cutaneous tuberculosis characterized by "apple-jelly nodules" on diascopy. It typically presents as plaques or ulcers rather than deep draining sinuses. * **Pediculosis:** This refers to infestation with lice (head, body, or pubic). It presents with pruritus and excoriations, not deep tissue destruction or sinus formation. **High-Yield Clinical Pearls for NEET-PG:** * **Eumycetoma:** Most common cause worldwide is *Madurella mycetomatis*. Grains are usually black or white. * **Actinomycetoma:** Most common cause in India is *Nocardia brasiliensis* or *Actinomadura madurae*. Grains are usually white, yellow, or red. * **Diagnosis:** Crushing the grains and performing Gram stain/KOH mount is the initial step. * **Dot-in-a-circle sign:** A characteristic MRI finding in Mycetoma where the "dot" represents the grain and the "circle" represents the inflammatory granuloma.

Question 217: Wood's light can be used for the evaluation of which of the following conditions?

A. Tinea capitis (Correct Answer)
B. Freckles
C. Vitiligo
D. Tuberous sclerosis

Explanation: **Explanation:** **Wood’s light (UV light with a wavelength of 365 nm)** is a diagnostic tool used in dermatology and microbiology to detect specific infections and pigmentary disorders based on characteristic fluorescence. **1. Why Tinea capitis is correct:** Wood’s light is a classic screening tool for Tinea capitis (fungal infection of the scalp). Certain dermatophytes produce **pteridine** metabolites that fluoresce under UV light. Specifically: * **Microsporum species** (e.g., *M. canis, M. audouinii*): Produce a brilliant **bright green/blue-green** fluorescence. * *Note:* Trichophyton species (except *T. schoenleinii*, which shows dull blue) generally do not fluoresce. **2. Why other options are incorrect:** * **Freckles (B):** These are areas of increased melanin. Under Wood’s light, epidermal pigmentation becomes more pronounced, but it is not a primary diagnostic indication for evaluation. * **Vitiligo (C):** While Wood’s light is used to detect Vitiligo (showing **milky-white** fluorescence due to total loss of melanin), the question asks for the evaluation of conditions in a microbiological context where Tinea capitis is the classic association. * **Tuberous Sclerosis (D):** Wood’s light helps identify **Ash-leaf spots** (hypopigmented macules) in fair-skinned individuals, but it is a supportive sign rather than the primary "evaluation" target compared to the diagnostic utility in fungal infections. **High-Yield Clinical Pearls for NEET-PG:** * **Erythrasma (*Corynebacterium minutissimum*):** Shows characteristic **Coral-red** fluorescence (due to porphyrins). * **Pityriasis versicolor (*Malassezia furfur*):** Shows **Yellowish-white/Copper-orange** fluorescence. * **Pseudomonas aeruginosa:** Shows **Yellow-green** fluorescence (due to pyoverdin) in burn wounds. * **Porphyria Cutanea Tarda:** Urine shows **Pink-red** fluorescence.

Question 218: Barrel-shaped spores are seen with which of the following fungi?

A. Blastomyces
B. Histoplasma
C. Coccidioides (Correct Answer)
D. Candida

Explanation: **Explanation:** The correct answer is **Coccidioides** (Option C). **Why Coccidioides is correct:** *Coccidioides immitis* and *C. posadasii* are dimorphic fungi characterized by a unique life cycle. In the environment (soil) and in laboratory cultures (at 25°C), they form septate hyphae that fragment into highly infectious, thick-walled, **barrel-shaped arthroconidia** (arthrospores). These spores are typically separated by empty "disjunctor cells," giving them a characteristic "beaded" or "barrel" appearance under the microscope. In the human body (37°C), these spores transform into large **spherules** filled with endospores. **Why other options are incorrect:** * **Blastomyces:** Characterized by large, round-to-oval yeast cells with a **broad-based bud** and a thick, "doubly refractile" cell wall. * **Histoplasma:** Typically seen as small, intracellular yeast cells within macrophages. They do not form barrel-shaped spores; their diagnostic feature in culture is the **tuberculate macroconidia** (finger-like projections). * **Candida:** A yeast-like fungus that primarily reproduces by budding (blastoconidia) and forms **pseudohyphae**. In specific conditions (e.g., Cornmeal agar), *C. albicans* forms thick-walled **chlamydospores**. **High-Yield Clinical Pearls for NEET-PG:** * **Coccidioidomycosis** is also known as **Valley Fever** or Desert Rheumatism. * It is the **most virulent** of the systemic mycoses; laboratory cultures are a major biohazard. * **Morphology Shift:** Arthroconidia (Environment/Culture) → Spherules (Tissue). * **Geographic distribution:** Southwestern USA (Arizona, California), Mexico, and Central/South America. * **Clinical Triad:** Fever, joint pain (arthralgia), and erythema nodosum.

Question 219: In a patient, corneal scraping reveals narrow angled septate hyphae. Which of the following is the likely etiological agent?

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

Explanation: **Explanation:** The clinical presentation of corneal scraping revealing **narrow-angled septate hyphae** is a classic description of **Aspergillus**, the most common cause of fungal keratitis worldwide. **1. Why Aspergillus is correct:** Aspergillus species are characterized morphologically by thin, **septate hyphae** that branch at **acute angles (approximately 45°)**. In the context of ophthalmology, *Aspergillus flavus* and *Aspergillus fumigatus* are frequent isolates following ocular trauma (often involving vegetative matter). **2. Why the other options are incorrect:** * **Mucor:** These belong to the Zygomycetes group and are characterized by **broad, aseptate (coenocytic) hyphae** that branch at **obtuse or right angles (90°)**. * **Histoplasma:** This is a dimorphic fungus. In tissue, it typically appears as small, intracellular **yeast cells** (often within macrophages), not as hyphae. * **Candida:** This is a yeast that typically produces **pseudohyphae** (constrictions at septa) and budding yeast cells (blastoconidia), rather than true septate hyphae with acute branching. **Clinical Pearls for NEET-PG:** * **Branching Pattern:** Remember the mnemonic **"A"** for **A**spergillus = **A**cute angle; **"M"** for **M**ucor = **M**ore than 90° (Obtuse). * **Fungal Keratitis:** Often presents with a "feathery" border on slit-lamp examination and satellite lesions. * **Culture:** Sabouraud Dextrose Agar (SDA) is the standard medium; Aspergillus colonies often appear velvety or powdery with distinct colors (e.g., green for *A. fumigatus*, yellow-green for *A. flavus*). * **Drug of Choice:** Topical Natamycin is the preferred treatment for filamentous fungal keratitis.

Question 220: A patient presents with foot swelling, pus discharge, and multiple sinuses. A KOH smear reveals filamentous structures. What is the most likely diagnosis?

A. Osteomyelitis
B. Madura mycosis (Correct Answer)
C. Anthrax
D. Actinomycosis

Explanation: ### Explanation The clinical presentation of **foot swelling, multiple discharging sinuses, and pus** is the classic triad of **Mycetoma** (Madura foot). **1. Why Madura Mycosis is correct:** Mycetoma can be caused by either fungi (**Eumycetoma/Madura mycosis**) or bacteria (**Actinomycetoma**). The key diagnostic clue here is the **KOH smear**, which reveals **filamentous structures** (fungal hyphae). In Madura mycosis, these hyphae are typically thick (2-4 μm) and septate. The presence of "grains" in the discharge is also a hallmark, representing colonies of the causative agent (e.g., *Madurella mycetomatis*). **2. Why other options are incorrect:** * **Actinomycosis:** While it also presents with sinuses and "sulfur granules," it typically involves the **cervicofacial region** (lumpy jaw). Under microscopy, *Actinomyces* are Gram-positive, branching, thin filamentous bacteria (not fungi), and are usually anaerobic. * **Osteomyelitis:** While chronic osteomyelitis can cause swelling and sinuses, it would not show filamentous structures on a KOH smear; it is typically caused by pyogenic bacteria like *Staphylococcus aureus*. * **Anthrax:** Cutaneous anthrax presents as a painless **black eschar** with surrounding edema, not chronic discharging sinuses. **3. High-Yield Clinical Pearls for NEET-PG:** * **Triad of Mycetoma:** Soft tissue swelling + Multiple discharging sinuses + Grains in pus. * **Eumycetoma (Fungal):** Caused by *Madurella mycetomatis* (Black grains). Shows thick hyphae on KOH. * **Actinomycetoma (Bacterial):** Caused by *Nocardia* or *Actinomadura*. Shows thin filaments (<1 μm) on Gram stain. * **Radiology:** The **"Dot-in-circle" sign** on MRI is pathognomonic for mycetoma.

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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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