Mycology Practice Questions

Q: Kerion is caused by:

Dermatophytes. **Explanation:** **Kerion** is a severe, inflammatory form of **Tinea Capitis** (fungal infection of the scalp). It is caused by a delayed-type hypersensitivity reaction to the metabolic products of **Dermatophytes**, most commonly zoophilic species like *Trichophyton verrucosum* (from cattle) or *Trichophyton mentagrophytes*. 1. **Why Dermatophytes are correct:** Kerion presents as a painful, boggy, inflammatory mass studded with pustules. It often leads to scarring alopecia if not treated promptly. The primary causative agents are dermatophytic fungi that invade the hair follicle, triggering an intense immune response. 2. **Why other options are incorrect:** * **Candida:** While *Candida* causes various mucocutaneous infections (like oral thrush or intertrigo), it does not typically cause the inflammatory follicular destruction seen in Kerion. * **Streptococcus:** This is a bacterium. While secondary bacterial infection (superinfection) can occur in a Kerion, the primary etiology is fungal. * **Herpes:** Herpes Simplex Virus (HSV) causes vesicular eruptions (e.g., herpes gladiatorum or cold sores) but does not present as a boggy, pustular scalp mass. **High-Yield NEET-PG Pearls:** * **Clinical Presentation:** "Boggy swelling," pustules, regional lymphadenopathy, and "Cigarette ash" appearance of broken hairs. * **Diagnosis:** KOH mount shows fungal hyphae/spores; Wood’s lamp may show fluorescence depending on the species. * **Treatment of Choice:** **Oral Griseofulvin** is the gold standard for Tinea Capitis/Kerion. Topical antifungals are insufficient as they do not penetrate the hair follicle. * **Complication:** Permanent scarring alopecia (cicatricial alopecia).

Q: Which hepatotoxic carcinogen is produced by?

Aspergillus flavus. **Explanation:** The correct answer is **Aspergillus flavus**. **1. Why Aspergillus flavus is correct:** *Aspergillus flavus* (and *A. parasiticus*) produces **Aflatoxins**, which are potent hepatotoxic and carcinogenic compounds. These fungi typically contaminate stored grains like groundnuts, maize, and rice. * **Mechanism:** Aflatoxin B1 is metabolized in the liver to a reactive epoxide that binds to DNA, causing a specific mutation in the **p53 tumor suppressor gene** (codon 249). * **Clinical Consequence:** Chronic exposure is a major risk factor for **Hepatocellular Carcinoma (HCC)**, especially in patients with co-existing Hepatitis B infection. **2. Why the other options are incorrect:** * **Claviceps fusiformis:** This fungus produces **Ergot alkaloids**. Ingestion leads to Ergotism (St. Anthony’s Fire), characterized by intense vasoconstriction leading to gangrene or neurological symptoms (convulsions), but it is not a primary hepatocarcinogen. * **Aspergillus fumigatus:** This is the most common cause of invasive Aspergillosis, Aspergilloma (fungal ball), and ABPA. It produces toxins like Gliotoxin (immunomodulatory), but not hepatotoxic aflatoxins. * **Argemone mexicana:** This is a weed whose seeds contaminate mustard oil. It contains **Sanguinarine**, which causes **Epidemic Dropsy** (characterized by edema, cardiac failure, and glaucoma), not hepatocarcinogenesis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Aflatoxin B1:** The most potent naturally occurring carcinogen. * **Diagnosis:** UV light can be used to detect aflatoxin in contaminated food (it shows a characteristic blue/green fluorescence). * **Other Mycotoxins to remember:** * **Ochratoxin:** Produced by *Aspergillus* and *Penicillium*; causes Nephrotoxicity. * **Zearalenone:** Produced by *Fusarium*; has estrogenic effects (precocious puberty).

Q: Sclerotic bodies are found in which of the following conditions?

Chromoblastomycosis. **Explanation:** **Chromoblastomycosis** is a chronic fungal infection of the skin and subcutaneous tissue caused by dematiaceous (pigmented) fungi like *Fonsecaea pedrosoi* and *Phialophora verrucosa*. The hallmark histological finding is the presence of **Sclerotic bodies** (also known as **Medlar bodies** or **Copper-penny bodies**). These are thick-walled, dark brown, multiseptate fungal cells that represent an intermediate stage between yeast and hyphae. They are pathognomonic for this condition and are seen within giant cells or microabscesses. **Analysis of Incorrect Options:** * **A. Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it is characterized by large, thick-walled **sporangia** containing thousands of endospores. It typically presents as friable, strawberry-like nasal polyps. * **B. Histoplasmosis:** Caused by *Histoplasma capsulatum*, it appears as small, oval **intracellular yeast cells** within macrophages, often surrounded by a narrow clear halo (pseudocapsule). * **C. Coccidiomycosis:** Caused by *Coccidioides immitis*, it is identified by large, thick-walled **spherules** filled with endospores in tissue sections. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Chromoblastomycosis typically presents as "cauliflower-like" verrucous lesions on the lower limbs of barefoot walkers. * **Diagnostic Clue:** Look for "black dots" on the surface of the lesion; these represent hemopurulent crusts containing the sclerotic bodies. * **Staining:** Sclerotic bodies are naturally pigmented (melanin) and can be seen on KOH mounts or H&E stains without special fungal stains. * **Treatment:** Itraconazole is the drug of choice, often combined with surgical excision or cryotherapy.

Q: Which of the following is FALSE about Sporothrix schenckii?

Sclerotic bodies are seen.. **Explanation:** **Sporothrix schenckii** is the causative agent of Sporotrichosis (Rose Gardener’s disease). The statement "Sclerotic bodies are seen" is **FALSE** because sclerotic bodies (also known as Medlar bodies or copper-penny bodies) are the pathognomonic histological hallmark of **Chromoblastomycosis**, not Sporotrichosis. **Analysis of Options:** * **Option B (Correct):** In Sporotrichosis, the characteristic histological finding is the **Asteroid body**, which consists of a central yeast cell surrounded by radiating eosinophilic material (Splendore-Hoeppli phenomenon). Sclerotic bodies are thick-walled, dark brown pigmented cells seen in Chromoblastomycosis. * **Option A:** It is indeed a **thermally dimorphic** fungus (Cigar-shaped yeast at 37°C; Mold with daisy-petal conidia at 25°C) that causes **subcutaneous** infections, typically following traumatic inoculation. * **Option C:** The **Splendore-Hoeppli phenomenon** is an antigen-antibody reaction seen around fungi or parasites in tissues. It is classically observed in Sporotrichosis (forming the Asteroid body). * **Option D:** **Itraconazole** is currently the drug of choice for cutaneous and lymphocutaneous sporotrichosis. (Note: Saturated Solution of Potassium Iodide/SSKI was the historical treatment). **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Nodular lesions along the line of lymphatic drainage (Lymphocutaneous distribution). * **Morphology:** "Cigar-shaped" yeast in tissue; "Daisy-head" arrangement of conidia on culture. * **Culture:** Sabouraud Dextrose Agar (SDA) shows moist, leathery colonies that turn black with age.

Q: What is the optimal pH condition for the growth of fungi that cause skin infections?

Acidic. **Explanation:** Fungi, particularly dermatophytes (the most common cause of skin infections), thrive in **acidic environments**, typically within a pH range of **5.0 to 6.0**. This preference aligns with the natural physiology of human skin, which maintains an "acid mantle" (pH 4.5–5.5) due to lactic acid and fatty acids in sweat and sebum. Fungi have evolved to utilize keratin as a nutrient source in these specific acidic conditions. **Analysis of Options:** * **A. Acidic (Correct):** Most pathogenic fungi are acidophilic. An acidic environment promotes the activity of fungal enzymes like keratinases, which break down skin proteins. * **B. Alkaline:** Alkaline conditions are generally inhibitory to fungal growth. In fact, many topical treatments aim to slightly alter the pH to discourage fungal colonization. * **C. Extremely acidic:** While fungi prefer acidity, extreme pH levels (below 3.0) can denature fungal proteins and inhibit growth, just as they would for most biological organisms. * **D. Neutral:** While some fungi can tolerate a neutral pH (7.0), it is not the *optimal* condition for those causing superficial mycoses. **High-Yield Clinical Pearls for NEET-PG:** * **Culture Media:** Sabouraud Dextrose Agar (SDA), the standard medium for fungal growth, is intentionally kept acidic (pH 5.6) to favor fungi while inhibiting bacterial contaminants. * **Dermatophytes:** The three main genera are *Trichophyton*, *Microsporum*, and *Epidermophyton*. * **Temperature:** Most systemic fungi are dimorphic (yeast at 37°C, mold at 25°C), but dermatophytes are typically cultured at room temperature (25–30°C). * **Wood’s Lamp:** Used to diagnose certain fungal infections (e.g., *Microsporum canis*), which fluoresce under UV light.

Q: All of the following are true about Cryptococcus EXCEPT:

Polysaccharide capsule. The correct answer is **A (Polysaccharide capsule)**. However, there is a technical nuance in the question framing: *Cryptococcus neoformans* is famously known for its thick polysaccharide capsule; therefore, if the question asks for the "EXCEPT" (the false statement), Option A is actually a **true** characteristic. In the context of standard NEET-PG patterns, the false statement (and thus the correct answer to the "Except" question) is **C (Pseudohyphae)**. ### **Explanation** 1. **Why Option C is the correct answer (The False Statement):** *Cryptococcus neoformans* is an **obligate yeast**. Unlike *Candida albicans*, it **does not form pseudohyphae** or true hyphae in clinical specimens or standard cultures. It exists almost exclusively as a round-to-oval budding yeast. 2. **Why the other options are True (Incorrect for "Except"):** * **Polysaccharide Capsule (A):** This is the most defining feature of *Cryptococcus*. The capsule (composed of Glucuronoxylomannan) is its primary virulence factor, protecting it from phagocytosis. * **Reproduces by Budding (B):** *Cryptococcus* reproduces via asexual budding. * **Narrow-based Budding (D):** A hallmark diagnostic feature of *Cryptococcus* is **narrow-based budding**, which distinguishes it from *Blastomyces* (which has a broad-based bud). ### **High-Yield NEET-PG Pearls** * **Stains:** Visualized using **India Ink** or Nigrosin (negative staining shows a clear halo). Specific stains for the capsule include **Mucicarmine** (bright red), PAS, and Alcian Blue. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA). On **Bird Seed Agar (Niger Seed Agar)**, it produces brown-black colonies due to phenoloxidase activity (melanin production). * **Clinical Presentation:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 <100). * **Biochemical Test:** It is **Urease positive**.

Q: Which fungus is usually not cultivable?

Rhinosporidium. **Explanation:** The correct answer is **Rhinosporidium seeberi**. Despite its name and historical classification, *Rhinosporidium seeberi* is an aquatic protist (Mesomycetozoea) that causes **Rhinosporidiosis**. It is unique in medical mycology because it has **never been successfully cultured** on artificial media (like SDA) or in cell lines. Diagnosis relies entirely on clinical presentation and histopathology showing characteristic large **sporangia** (up to 350 µm) containing thousands of **endospores**. **Why the other options are incorrect:** * **Cryptococcus:** *C. neoformans* grows readily on Sabouraud Dextrose Agar (SDA) and Bird Seed Agar (Niger seed agar), where it produces characteristic brown-pigmented colonies due to phenoloxidase activity. * **Dermatophytes:** Fungi like *Trichophyton*, *Microsporum*, and *Epidermophyton* are easily cultured on SDA with actidione (cycloheximide). They are identified by their macro and microconidia. * **Histoplasma:** As a dimorphic fungus, *H. capsulatum* can be cultured at 25°C (mycelial form with tuberculate macroconidia) and 37°C (yeast form). **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Associated with stagnant water; common in South India (Tamil Nadu, Kerala) and Sri Lanka. * **Clinical Presentation:** Presents as friable, leafy, strawberry-like **polypoidal masses** in the nose or nasopharynx. * **Transmission:** Traumatic inoculation (e.g., sand/dust) or diving into infected water. * **Treatment:** Surgical excision with wide-base cauterization is the treatment of choice; medical therapy (Dapsone) has limited efficacy.

Q: Microscopic examination of a patient's sputum shows aseptate fungus. Which of the following is an aseptate fungus?

Rhizopus. ### Explanation The correct answer is **Rhizopus**. **1. Why Rhizopus is correct:** Rhizopus belongs to the class **Zygomycetes** (Mucormycetes). The hallmark microscopic feature of Zygomycetes (including *Mucor* and *Rhizopus*) is the presence of **broad, ribbon-like, aseptate (or sparsely septate) hyphae** that branch at wide angles (90°, right-angled branching). In clinical specimens like sputum or tissue biopsies, these fungi are easily identified by their lack of cross-walls (septa). **2. Why the other options are incorrect:** * **Aspergillus:** This is a filamentous fungus characterized by **narrow, septate hyphae** that exhibit **acute-angle branching** (typically 45°). This is the most common differential for Rhizopus. * **Candida:** This is primarily a **yeast** that reproduces by budding. It forms **pseudohyphae** (elongated buds with constrictions at the septa) and true hyphae (which are septate), but it is not an aseptate filamentous fungus. * **Nocardia:** This is not a fungus but a **Gram-positive, filamentous bacterium**. It is characterized by thin, branching filaments that are weakly acid-fast. **3. Clinical Pearls for NEET-PG:** * **Rhizopus/Mucormycosis:** Strongly associated with **uncontrolled Diabetes Mellitus** (especially Ketoacidosis) and neutropenia. It has a predilection for blood vessels (**angioinvasion**), leading to infarction and necrosis. * **Culture:** On Sabouraud Dextrose Agar (SDA), Rhizopus is known as a **"lid lifter"** because of its rapid, fluffy growth that fills the petri dish. * **Morphology Hint:** Remember **"A"** for **A**spergillus = **A**cute angle + **A**septate (False, it is Septate). Use the mnemonic: **M**ucor is **W**ide (**M** flipped is **W**) = **W**ide angle + **W**ithout septa.

Question 1

Kerion is caused by:

Accepted Answer

Dermatophytes

Answer

Candida

Answer

Streptococcus

Answer

Herpes

Question 2

Which hepatotoxic carcinogen is produced by?

Accepted Answer

Aspergillus flavus

Answer

Claviceps fusiformis

Answer

Aspergillus fumigatus

Answer

Argemone mexicana

Question 3

Coccidioides immitis is identified in tissues on the basis of which of the following?

Accepted Answer

Yeast-like forms with very large capsules

Answer

Budding yeast cells with pseudohyphae

Answer

Arthrospores

Answer

Endosporulating spherules

Question 4

Sclerotic bodies are found in which of the following conditions?

Accepted Answer

Chromoblastomycosis

Answer

Rhinosporidiosis

Answer

Histoplasmosis

Answer

Coccidiomycosis

Question 5

Which of the following is FALSE about Sporothrix schenckii?

Accepted Answer

Sclerotic bodies are seen.

Answer

It is a dimorphic subcutaneous fungus.

Answer

Splendore-Hoeppli phenomenon is observed.

Answer

Itraconazole is the drug of choice.

Question 6

What is the optimal pH condition for the growth of fungi that cause skin infections?

Accepted Answer

Acidic

Answer

Alkaline

Answer

Extremely acidic

Answer

Neutral

Question 7

Phagocytosis of Cryptococcus neoformans is inhibited by which of the following?

Accepted Answer

Cryptococcal capsular material

Answer

The size of the yeast cells

Answer

The cell walls

Answer

Toxins produced by the organism

Question 8

All of the following are true about Cryptococcus EXCEPT:

Accepted Answer

Polysaccharide capsule

Answer

Reproduces by budding

Answer

Pseudohyphae

Answer

Mycelium have a narrow base

Question 9

Which fungus is usually not cultivable?

Accepted Answer

Rhinosporidium

Answer

Cryptococcus

Answer

Dermatophytes

Answer

Histoplasma

Question 10

Microscopic examination of a patient's sputum shows aseptate fungus. Which of the following is an aseptate fungus?

Accepted Answer

Rhizopus

Answer

Aspergillus

Answer

Candida

Answer

Nocardia

Mycology — MCQs

Mycology — MCQs

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