Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 81: Actinomycetoma is caused by all of the following EXCEPT:

A. Actinomyces
B. Nocardia
C. Streptomyces
D. Madura mycosis (Correct Answer)

Explanation: **Explanation:** Mycetoma is a chronic, granulomatous, subcutaneous infection characterized by a triad of **localized swelling, underlying bone destruction, and the presence of discharging sinuses containing grains.** It is etiologically classified into two types: 1. **Actinomycetoma:** Caused by filamentous aerobic bacteria. 2. **Eumycetoma:** Caused by true fungi. **Why "Madura mycosis" is the correct answer:** Madura mycosis (or Eumycetoma) is caused by true fungi, most commonly *Madurella mycetomatis*. It is distinct from Actinomycetoma because it requires antifungal therapy (e.g., Itraconazole) and often surgical intervention, whereas Actinomycetoma is treated with long-term antibiotics (e.g., Welsh regimen). **Analysis of Incorrect Options:** * **Actinomyces:** While *Actinomyces israelii* typically causes endogenous actinomycosis, certain species can cause actinomycetoma. * **Nocardia:** Species like *Nocardia brasiliensis* are the most common cause of actinomycetoma worldwide. * **Streptomyces:** *Streptomyces somaliensis* is a well-recognized causative agent of actinomycetoma, often producing yellow/white grains. **High-Yield Clinical Pearls for NEET-PG:** * **Grains:** The color of the grain provides a diagnostic clue. **Black grains** are pathognomonic for Eumycetoma (*Madurella*). **Yellow/White grains** can be seen in both, but are common in *Nocardia* and *Streptomyces*. * **Treatment:** Actinomycetoma responds well to the **Welsh Regimen** (Amikacin + Cotrimoxazole). * **Diagnosis:** The most definitive diagnosis is made by histopathological examination of the grains and culture on Sabouraud Dextrose Agar (SDA) or Lowenstein-Jensen (LJ) medium.

Question 82: Which of the following Aspergillus species produces black-colored colonies on Sabouraud's dextrose agar?

A. A. fumigatus
B. A. niger (Correct Answer)
C. A. flavus
D. None of the above

Explanation: **Explanation:** The correct answer is **B. A. niger**. **Aspergillus niger** is characterized by its rapid growth on Sabouraud’s Dextrose Agar (SDA), initially appearing white but quickly turning into a dense, **carbon-black** color. This pigmentation is due to the production of dark conidia (spores) on the surface of the colony. Microscopically, it features large, globose, black conidial heads with "biseriate" sterigmata covering the entire vesicle. **Analysis of Incorrect Options:** * **A. fumigatus:** This is the most common pathogenic species. It produces **smoky-green** or grayish-green colonies. It is known for its thermotolerance (growing at 45°C) and "uniseriate" phialides. * **C. A. flavus:** This species typically produces **yellowish-green** or lime-green colonies. It is clinically significant for producing **Aflatoxins**, which are linked to hepatocellular carcinoma. * **D. None of the above:** Incorrect, as A. niger is the classic "black mold." **High-Yield Clinical Pearls for NEET-PG:** 1. **Otomycosis:** *A. niger* is the most common cause of fungal otitis externa, often presenting with a "wet newspaper" appearance or black specks in the ear canal. 2. **Oxalate Crystals:** *A. niger* is unique for producing calcium oxalate crystals in tissue or sputum, which can be a diagnostic clue in biopsies. 3. **Aspergilloma:** While *A. fumigatus* is the primary cause of "fungus balls" in pre-existing lung cavities, all three species mentioned can be involved. 4. **Morphology:** Remember the color mnemonic: **F**umigatus (**F**orest/Green), **Fl**avus (**Fl**uorescent/Yellow-Green), **N**iger (**N**ight/Black).

Question 83: Broad based budding is seen in which of the following fungal infections?

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

Explanation: ### Explanation **Blastomycosis (*Blastomyces dermatitidis*)** is the correct answer because it is characterized by a unique morphological feature known as **Broad-Based Budding**. In tissue samples (yeast phase), the daughter cell remains attached to the mother cell by a wide neck, making the base of the bud nearly as wide as the cell itself. The yeast cells are typically large (8–15 µm) with thick, "doubly refractile" walls. #### Analysis of Incorrect Options: * **A. Coccidiomycosis:** Does not exist as yeast in tissue. Instead, it forms large **spherules** (20–100 µm) filled with numerous small **endospores**. * **B. Paracoccidiomycosis:** Characterized by multiple narrow-based buds surrounding a central large yeast cell, resembling a **"Pilot’s Wheel"** or **"Mickey Mouse"** appearance. * **C. Cryptococcosis:** This is a monomorphic yeast characterized by **narrow-based budding** and a prominent polysaccharide capsule (visualized with India Ink). #### NEET-PG High-Yield Pearls: * **Blastomycosis Mnemonic:** "B" for **B**lasto, **B**road-based budding, **B**one involvement (common site of dissemination), and **B**ig (large yeast). * **Geographic distribution:** Primarily found in the Ohio and Mississippi River Valleys (similar to Histoplasmosis). * **Dimorphism:** These fungi are "molds in the cold (25°C) and yeasts in the heat (37°C)." * **Histoplasmosis (Comparison):** Shows small, intracellular yeasts within macrophages (no broad budding).

Question 84: Which of the following statements regarding Candida are true?

A. Commensal in skin (Correct Answer)
B. Oral candidiasis is common in pregnancy
C. In AIDS, it occurs at an early stage
D. Gram staining is done

Explanation: **Explanation:** *Candida albicans* is a versatile opportunistic fungus. Understanding its ecological niche and clinical presentation is crucial for NEET-PG. **1. Why Option A is Correct:** *Candida* species are part of the **normal human flora (commensals)**. They primarily colonize the gastrointestinal tract (mouth to anus), the female genital tract (vagina), and the **skin**, particularly in moist areas (intertriginous sites). When the host's local or systemic immunity is compromised, these commensals transition into pathogens. **2. Analysis of Incorrect Options:** * **Option B:** While pregnancy predisposes women to **Vulvovaginal Candidiasis** (due to high estrogen levels and increased glycogen content in the vaginal mucosa), **oral candidiasis** is not specifically "common" in pregnancy; it is more characteristic of T-cell deficiencies or inhaled steroid use. * **Option C:** In HIV/AIDS patients, *Candida* infections follow a specific hierarchy. **Oropharyngeal Candidiasis** (Thrush) occurs at a relatively early stage (CD4 count <500 cells/mm³), but **Esophageal Candidiasis** is an AIDS-defining illness occurring at a later, more advanced stage (CD4 <200 cells/mm³). * **Option D:** While *Candida* can be visualized on a Gram stain (appearing as large, Gram-positive budding yeast cells), the statement is technically less definitive as a "characteristic" compared to its commensal nature. However, in many exam contexts, Option A is the established physiological fact. **High-Yield Clinical Pearls:** * **Morphology:** *Candida* is dimorphic; it forms **Pseudohyphae** in tissues, but *C. albicans* specifically produces **Germ Tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as creamy white, smooth colonies with a "yeasty" odor. * **Chlamydospores:** *C. albicans* produces thick-walled terminal chlamydospores on Cornmeal Agar.

Question 85: What is the culture medium used for fungi?

A. Tellurite medium
B. NNN medium
C. Chocolate agar
D. SDA (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. SDA (Sabouraud Dextrose Agar)** Sabouraud Dextrose Agar (SDA) is the standard primary isolation medium for fungi. It has a low pH (around 5.6), which inhibits the growth of most bacteria while favoring fungal proliferation. It consists of dextrose (energy source), peptone (nitrogen source), and agar. To make it more selective, antibiotics like chloramphenicol (to inhibit bacteria) or cycloheximide (to inhibit saprophytic fungi) are often added. **Analysis of Incorrect Options:** * **A. Tellurite medium:** Specifically, Potassium Tellurite agar (e.g., Hoyle’s or McLeod’s) is used for the isolation of *Corynebacterium diphtheriae*. The bacteria reduce tellurite to metallic tellurium, resulting in characteristic black colonies. * **B. NNN medium (Novy-MacNeal-Nicolle):** This is a specialized enriched medium used for the cultivation of Hemoflagellates, specifically *Leishmania donovani* and *Trypanosoma cruzi*. * **C. Chocolate agar:** This is an enriched medium containing lysed red blood cells. It is used for fastidious bacteria such as *Neisseria meningitidis* and *Haemophilus influenzae*. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation:** Fungal cultures are typically incubated at **25°C and 37°C** to demonstrate dimorphism. * **Duration:** Most fungi require **1–3 weeks** of incubation; however, *Candida* grows within 24–48 hours. * **Other Fungal Media:** * **Cornmeal Agar:** Used to demonstrate chlamydospore formation in *Candida albicans*. * **Niger Seed Agar (Birdseed Agar):** Used for the identification of *Cryptococcus neoformans* (produces brown colonies due to phenol oxidase activity). * **Czapek Dox Agar:** Used for the identification of *Aspergillus* species.

Question 86: Which stain is used to differentiate Cryptococcus from other fungi?

A. Gram Stain
B. Wright-Giemsa
C. India ink (Correct Answer)
D. Toluidine blue

Explanation: **Explanation:** **Correct Answer: C. India ink** The defining characteristic of *Cryptococcus neoformans* is its thick, **polysaccharide capsule**. India ink (and Nigrosin) are negative stains; the large carbon particles cannot penetrate the capsule. Under a microscope, this creates a classic "halo" effect—a clear, translucent zone surrounding the yeast cell against a dark background. This is the gold-standard rapid bedside test for diagnosing Cryptococcal meningitis using cerebrospinal fluid (CSF). **Analysis of Incorrect Options:** * **A. Gram Stain:** While *Cryptococcus* is Gram-positive, it often appears as "irregularly stained" or "ghost cells" because the capsule prevents consistent dye uptake. It does not differentiate it from other yeasts like *Candida*. * **B. Wright-Giemsa:** This is a hematological stain used primarily for intracellular pathogens (like *Histoplasma capsulatum* in macrophages) or peripheral blood smears, but it does not highlight the capsule specifically. * **D. Toluidine blue:** This stain is primarily used to identify *Pneumocystis jirovecii* cysts in respiratory specimens, appearing as crushed ping-pong balls. **High-Yield Clinical Pearls for NEET-PG:** * **Most Sensitive Test:** While India ink is classic, the **Cryptococcal Antigen (CrAg) test** (Lateral Flow Assay) is more sensitive and specific. * **Culture:** Sabouraud Dextrose Agar (SDA) produces creamy, mucoid colonies. * **Biopsy Stains:** To visualize the capsule in tissue sections, **Mucicarmine** (stains capsule red) or **Alcian Blue** are used. * **Biochemical Key:** *Cryptococcus* is **Urease positive**, which differentiates it from *Candida*.

Question 87: Which of the following fungi is NOT thermally dimorphic?

A. Sporothrix schenkii
B. Cryptococcus neoformans (Correct Answer)
C. Blastomyces dermatitidis
D. Histoplasma capsulatum

Explanation: **Explanation:** The concept of **thermal dimorphism** refers to fungi that exist in two distinct morphological forms depending on the temperature: a **mold** (filamentous) form in the environment/culture at 25°C and a **yeast** (unicellular) form in host tissues at 37°C. **Why Cryptococcus neoformans is the correct answer:** *Cryptococcus neoformans* is **not** thermally dimorphic. It is an **obligate yeast** (monomorphic), meaning it exists as a budding yeast with a prominent polysaccharide capsule both in the environment and within the human body at all temperatures. **Analysis of Incorrect Options:** * **Sporothrix schenckii:** A classic dimorphic fungus causing "Rose gardener’s disease." It exists as mold (septate hyphae with rosette-like conidia) at 25°C and as "cigar-shaped" budding yeast at 37°C. * **Blastomyces dermatitidis:** A dimorphic fungus that causes systemic mycosis. In tissues (37°C), it appears as a characteristic large yeast with a **broad-based bud**. * **Histoplasma capsulatum:** A dimorphic fungus found in soil with bird/bat droppings. At 37°C, it presents as small intracellular yeasts within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Dimorphic Fungi:** "**B**ody **H**eats **P**robably **S**hape **C**hange" (**B**lastomyces, **H**istoplasma, **P**aracoccidioides, **S**porothrix, **C**occidioides). Note: *Coccidioides* is dimorphic but forms **spherules** (not yeast) in the tissue. * *Cryptococcus* is best visualized using **India Ink** (negative staining) to highlight the capsule. * The most sensitive screening test for Cryptococcosis is the **Lateral Flow Assay (LFA)** for capsular antigen.

Question 88: Which of the following is not an opportunistic infection in AIDS?

A. Cryptococcus
B. Aspergillosis
C. Dermatophyte (Correct Answer)
D. Pneumocystis jirovecii

Explanation: **Explanation:** In the context of HIV/AIDS, **opportunistic infections (OIs)** are defined as infections that occur more frequently or are more severe in individuals with weakened immune systems (specifically when CD4+ T-cell counts drop). **Why Dermatophytes are the correct answer:** Dermatophytes (e.g., *Trichophyton*, *Microsporum*, and *Epidermophyton*) are **superficial mycoses** that infect keratinized tissues like skin, hair, and nails. While they can occur in AIDS patients, they are not classified as "opportunistic infections" because they commonly affect immunocompetent individuals and do not cause life-threatening systemic disease even in the presence of severe immunosuppression. In AIDS patients, dermatophytoses may present more extensively or atypically, but they remain localized to the integumentary system. **Analysis of Incorrect Options:** * **Cryptococcus neoformans:** A major OI in AIDS (usually when CD4 <100 cells/mm³). It is the most common cause of fungal meningitis in these patients. * **Aspergillosis:** While more common in neutropenic patients, *Aspergillus* species act as opportunistic pathogens in advanced AIDS, causing invasive pulmonary disease. * **Pneumocystis jirovecii:** Historically the most common defining OI in AIDS. It causes *Pneumocystis* pneumonia (PCP) typically when CD4 counts fall below 200 cells/mm³. **High-Yield Clinical Pearls for NEET-PG:** * **CD4 <200:** Threshold for *Pneumocystis jirovecii* prophylaxis (Trimethoprim-Sulfamethoxazole). * **CD4 <100:** Threshold for *Cryptococcus* and *Toxoplasma* risk. * **Diagnosis:** Cryptococcus is identified via **India Ink** preparation (capsule visualization) or Cryptococcal Antigen (CrAg) test. * **Pneumocystis:** Identified via **Gomori Methenamine Silver (GMS)** stain showing "crushed ping-pong ball" appearance.

Question 89: A patient presents with sulphur granules discharging from a sinus tract. This finding is suggestive of infection with which of the following?

A. Staphylococcus
B. Haemophilus ducreyi
C. Mycetoma (Correct Answer)
D. Sporotrichosis

Explanation: ### Explanation **Correct Answer: C. Mycetoma** **Concept:** The presence of **sulphur granules** in a discharging sinus tract is a classic clinical hallmark of **Mycetoma** (specifically Actinomycetoma). Mycetoma is a chronic, granulomatous infection of the subcutaneous tissue, characterized by a clinical triad: localized swelling, multiple interconnecting sinus tracts, and the discharge of grains (granules). These "sulphur granules" are actually micro-colonies of the causative organism (e.g., *Actinomyces israelii* or *Nocardia*) embedded in tissue debris and calcium. **Analysis of Incorrect Options:** * **A. Staphylococcus:** While *Staphylococcus aureus* can cause chronic osteomyelitis or abscesses, it typically produces creamy yellow pus, not organized granules or sinus tracts with grains. * **B. Haemophilus ducreyi:** This is the causative agent of **Chancroid**, characterized by painful genital ulcers and inguinal lymphadenopathy (buboes), but it does not produce sulphur granules. * **C. Sporotrichosis:** Caused by *Sporothrix schenckii*, this presents as "Rose Gardener’s Disease" with linear nodules along lymphatic drainage (sporotrichoid spread). It does not typically form granules in the discharge. **High-Yield Clinical Pearls for NEET-PG:** * **Actinomycetoma vs. Eumycetoma:** Actinomycetoma is caused by filamentous bacteria (e.g., *Actinomadura*, *Nocardia*), while Eumycetoma is caused by true fungi (e.g., *Madurella mycetomatis*). * **Granule Color:** * **Yellow/White:** *Actinomyces israelii* (classic "sulphur" granules), *Nocardia*. * **Black:** *Madurella mycetomatis* (Eumycetoma). * **Red:** *Actinomadura pelletieri*. * **Diagnosis:** Crushing the granule and performing a Gram stain or KOH mount is the initial step. *Actinomyces* are Gram-positive, non-acid-fast branching filaments.

Question 90: What is the primary site of infection in Cryptococcosis?

A. Adrenal glands
B. Bone
C. Central nervous system
D. Lungs (Correct Answer)

Explanation: ### Explanation **Primary Site of Infection: Lungs** *Cryptococcus neoformans* is an encapsulated yeast found primarily in soil enriched with pigeon droppings. The infection is acquired through the **inhalation** of basidiospores or desiccated yeast cells. Therefore, the **lungs** are the primary portal of entry and the initial site of infection. While many pulmonary infections remain asymptomatic or subclinical in immunocompetent individuals, the fungus can establish a primary focus here before disseminating hematogenously. **Analysis of Incorrect Options:** * **Central Nervous System (C):** This is the most common site of **clinical presentation** and the most serious manifestation (Cryptococcal meningitis). However, it is a secondary site resulting from hematogenous dissemination from the lungs. * **Bone (B) & Adrenal Glands (A):** These are rare sites of disseminated disease. While *Cryptococcus* can spread to almost any organ in severely immunocompromised patients (like those with advanced HIV/AIDS), they are never the primary site of entry. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The most important virulence factor is the **polysaccharide capsule** (detected by India Ink or Latex Agglutination). * **Diagnosis:** **India Ink** preparation of CSF shows a "halo" appearance. **Mucicarmine stain** is specific for the capsule (stains red). * **Culture:** Grows on Sabouraud Dextrose Agar (SDA); produces **urease** and forms brown/black colonies on **Niger Seed/Bird Seed Agar** (due to phenoloxidase activity). * **Treatment:** Induction therapy usually involves **Amphotericin B + Flucytosine**, followed by Fluconazole for maintenance.

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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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