Mycology Practice Questions

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: 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: Muriform cells are characteristically seen in which of the following conditions?

Chromoblastomycosis. **Explanation:** **Chromoblastomycosis** is a chronic localized fungal infection of the subcutaneous tissue caused by dematiaceous (pigmented) fungi, most commonly *Fonsecaea pedrosoi*. The hallmark histopathological finding is the presence of **Muriform cells**, also known as **Medlar bodies, Sclerotic bodies, or Copper-penny bodies**. These are thick-walled, dark brown, globe-shaped structures that divide by internal septation (binary fission) rather than budding. Their presence is pathognomonic for this condition. **Analysis of Incorrect Options:** * **Phaeohyphomycosis:** While also caused by pigmented fungi, it is characterized by the presence of pigmented **hyphae and yeast-like forms** in tissue, but it lacks the characteristic muriform cells. * **Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it is characterized by large **sporangia** (up to 300 µm) containing thousands of tiny **endospores**, typically presenting as friable nasal polyps. * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically shows a granulomatous reaction with the presence of **Asteroid bodies** (central yeast cell surrounded by eosinophilic radiating spicules) or cigar-shaped yeast cells. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Often presents as a "cauliflower-like" warty growth, usually on the lower limbs of barefoot workers. * **Pathology:** Look for the "Copper-penny" appearance in a KOH mount or skin biopsy. * **Transepidermal Elimination:** The skin attempts to expel these sclerotic bodies through the epidermis, a process visible on histopathology. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.

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.

Q: A 20-year-old uncontrolled diabetic presents with sinus swelling and a black necrotic mass in the nasal cavity. Which organism is most likely responsible?

Mucormycosis. ### Explanation **Correct Answer: A. Mucormycosis** The clinical presentation of a **diabetic patient** with **sinus swelling** and a **black necrotic mass** (eschar) is a classic description of **Rhinocerebral Mucormycosis**. * **Pathophysiology:** Mucormycosis (caused by *Rhizopus*, *Mucor*, or *Lichtheimia*) is an opportunistic fungal infection. In diabetic ketoacidosis (DKA), the fungi utilize ketone reductase to thrive in acidic, glucose-rich environments. * **The "Black Eschar":** These fungi are **angioinvasive**, meaning they invade blood vessel walls, leading to thrombosis and subsequent tissue infarction. This necrosis manifests clinically as the characteristic black eschar in the nasal cavity or palate. --- ### Why the other options are incorrect: * **B. Actinomycosis:** Caused by *Actinomyces israelii* (a filamentous bacterium, not a fungus). It typically presents as "lumpy jaw" with chronic abscesses and **sulfur granules** in the pus, not acute necrotic masses in diabetics. * **C. Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*. It presents as friable, **strawberry-like leafy polyps** in the nose, usually in patients with a history of bathing in stagnant water. It is not associated with diabetes or necrosis. * **D. Cryptococcus:** Primarily causes meningitis or pulmonary infections in immunocompromised patients. It does not typically cause angioinvasive sinus necrosis. --- ### High-Yield Clinical Pearls for NEET-PG: 1. **Microscopy:** Look for **broad, aseptate hyphae** with **branching at right angles (90°)**. (Contrast with *Aspergillus*, which has narrow, septate hyphae branching at 45°). 2. **Risk Factors:** Uncontrolled Diabetes (DKA), neutropenia, and iron overload (use of deferoxamine). 3. **Treatment:** Immediate surgical debridement and intravenous **Liposomal Amphotericin B**. 4. **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as "cotton candy" colonies.

Q: Melanized sclerotic cells / Medlar bodies (4-12 mm diameter) evident in this H & E stained cutaneous biopsy are characteristic of which disease?

Chromoblastomycosis. ***Chromoblastomycosis*** - **Melanized sclerotic cells** (also called **Medlar bodies** or **copper pennies**) are the **pathognomonic histopathological hallmark** of chromoblastomycosis. - These thick-walled, **brown-pigmented spherical cells** (4-12 mm) with **transverse and longitudinal septations** are diagnostic and distinguish it from other fungal infections. *Rhinosporidiosis* - Characterized by large **sporangia** containing **endospores**, not melanized sclerotic cells. - Caused by **Rhinosporidium seeberi** and typically affects **nasal mucosa** and **conjunctiva**. *Coccidioidomycosis* - Shows **spherules** filled with **endospores** in tissue, not melanized sclerotic cells. - Caused by **Coccidioides immitis/posadasii** and commonly affects **lungs** rather than skin. *Sporotrichosis* - Demonstrates **cigar-shaped yeasts** or **asteroid bodies** in tissue sections. - Caused by **Sporothrix schenckii** complex and typically shows **lymphocutaneous spread** pattern.

Q: Which of the following statements about Cryptococcus is FALSE?

Is urease negative. **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that is a significant pathogen, particularly in immunocompromised patients (e.g., those with HIV/AIDS). **1. Why Option B is the Correct (False) Statement:** The statement "Is urease negative" is incorrect because **Cryptococcus is characteristically urease positive.** This is a key biochemical marker used in the laboratory to differentiate it from other yeasts like *Candida albicans* (which is urease negative). The production of the urease enzyme allows the organism to hydrolyze urea into ammonia, which can be detected by a color change in Christensen’s urea agar. **2. Analysis of Other Options:** * **Option A (Primarily infects the lung):** This is true. The primary route of infection is the inhalation of basidiospores from the environment (often associated with pigeon droppings). While it is famous for causing meningitis, the **lung is the primary portal of entry** and the initial site of infection. * **Option C (Diagnosis aided by India ink):** This is true. The large polysaccharide capsule of *Cryptococcus* does not take up the ink, creating a characteristic **"halo" appearance** against a dark background. This is a classic, rapid bedside test for CSF samples. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **Polysaccharide Capsule** (GXM) is the most important virulence factor; it is antiphagocytic. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as mucoid, cream-colored colonies. * **Phenoloxidase Enzyme:** *Cryptococcus* produces melanin when grown on **Niger Seed Agar (Bird Seed Agar)**, appearing as brown/black colonies. * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test via Latex Agglutination or LFA is more sensitive and specific than India ink. * **Treatment:** Induction therapy usually involves **Amphotericin B + Flucytosine**, followed by Fluconazole.

Q: Which of the following statements regarding Candida is true?

Candida is a commensal on the skin.. **Explanation:** **1. Why Option A is Correct:** *Candida albicans* and other species are part of the normal human flora. While they are primarily known as commensals of the **gastrointestinal tract** and **genitourinary tract**, they are also found as commensals on the **skin**, particularly in moist areas (intertriginous sites). Under conditions of immunosuppression or disrupted mucosal integrity, these commensals transition into opportunistic pathogens. **2. Why the Other Options are Incorrect:** * **Option B:** Oral candidiasis (thrush) is more common in infants, denture wearers, and the immunocompromised. **Vaginal candidiasis**, however, is the form specifically associated with pregnancy due to high estrogen levels and increased glycogen content in the vaginal mucosa. * **Option C:** Candida infections (specifically esophageal candidiasis) are considered **AIDS-defining illnesses**, typically occurring when the CD4 count falls below **200 cells/mm³**. This usually represents a late/advanced stage of HIV infection, not the early stage. * **Option D:** While *Candida* appears as Gram-positive budding yeast cells on a Gram stain, the **KOH (Potassium Hydroxide) mount** or **culture (Sabouraud Dextrose Agar)** are the preferred diagnostic methods. KOH dissolves host cellular debris, making the pseudohyphae and yeast cells more visible. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *C. albicans* is unique because it produces **Germ Tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C for 2-3 hours. * **Culture:** On SDA, it forms creamy white, smooth colonies with a characteristic "yeasty" odor. * **Chlamydospores:** Produced on Cornmeal Agar (CMA). * **Drug of Choice:** Fluconazole is used for most localized infections; Echinocandins (e.g., Caspofungin) are preferred for systemic candidemia [1].

Question 1

Which hepatotoxic carcinogen is produced by?

Accepted Answer

Aspergillus flavus

Answer

Claviceps fusiformis

Answer

Aspergillus fumigatus

Answer

Argemone mexicana

Question 2

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 3

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 4

Muriform cells are characteristically seen in which of the following conditions?

Accepted Answer

Chromoblastomycosis

Answer

Phaeohyphomycosis

Answer

Rhinosporidiosis

Answer

Sporotrichosis

Question 5

Which fungus is usually not cultivable?

Accepted Answer

Rhinosporidium

Answer

Cryptococcus

Answer

Dermatophytes

Answer

Histoplasma

Question 6

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

Question 7

A 20-year-old uncontrolled diabetic presents with sinus swelling and a black necrotic mass in the nasal cavity. Which organism is most likely responsible?

Accepted Answer

Mucormycosis

Answer

Actinomycosis

Answer

Rhinosporidiosis

Answer

Cryptococcus

Question 8

Melanized sclerotic cells / Medlar bodies (4-12 mm diameter) evident in this H & E stained cutaneous biopsy are characteristic of which disease?

Accepted Answer

Chromoblastomycosis

Answer

Rhinosporidiosis

Answer

Coccidioidomycosis

Answer

Sporotrichosis

Question 9

Which of the following statements about Cryptococcus is FALSE?

Accepted Answer

Is urease negative

Answer

Primarily infects the lung

Answer

Diagnosis can be aided by India ink staining

Answer

All the other statements are true

Question 10

Which of the following statements regarding Candida is true?

Accepted Answer

Candida is a commensal on the skin.

Answer

Oral candidiasis is common during pregnancy.

Answer

Candida infections are common in the early stage of AIDS.

Answer

Gram staining is the preferred method for diagnosing Candida infections.

Mycology — MCQs

Mycology — MCQs

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