Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 61: Pneumocystis jirovecii is a:

A. Fungus (Correct Answer)
B. Protozoan
C. Gram-negative bacterium
D. None of the above

Explanation: **Explanation:** *Pneumocystis jirovecii* was historically classified as a protozoan due to its morphological features (cysts and trophozoites) and its lack of response to traditional antifungal drugs like Amphotericin B. However, modern molecular techniques, specifically **rRNA sequence analysis**, have definitively reclassified it as a **fungus**. **Why the correct answer is right:** * **Genetic Evidence:** DNA analysis shows it is closely related to Ascomycetous fungi. * **Cell Wall Composition:** Its cell wall contains **beta-1,3-glucan**, a characteristic fungal component (though it notably lacks ergosterol, which explains its resistance to many antifungals). **Why incorrect options are wrong:** * **B. Protozoan:** This was the old classification based on its life cycle stages. Unlike protozoa, *P. jirovecii* cannot be cultured in standard media and lacks certain protozoal organelles. * **C. Gram-negative bacterium:** It does not possess a bacterial cell wall or prokaryotic internal structures. While it is treated with Trimethoprim-Sulfamethoxazole (an antibacterial), this is due to its specific metabolic pathways, not its classification. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** It cannot be seen on Gram stain. The gold standard is **Gomori Methenamine Silver (GMS)** stain, which shows "crushed ping-pong ball" shaped cysts. * **Clinical Presentation:** It causes **Pneumocystis Pneumonia (PCP)**, an opportunistic infection in HIV patients (CD4 count <200 cells/µL). * **Radiology:** Characterized by bilateral, perihilar "ground-glass" opacities. * **Treatment of Choice:** High-dose **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if $PaO_2 < 70$ mmHg.

Question 62: A 40-year-old man presents with an ulcerative lesion on his right thumb, sustained while gardening. Culture reveals moist, creamy colonies. What is the most common causative organism?

A. Blastomyces
B. Phaeohyphomycosis
C. Rhinosporidium
D. Sporothrix (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Sporothrix** **Reasoning:** The clinical presentation describes a classic case of **Sporotrichosis** (Rose Gardener’s disease). The key diagnostic clues are the **traumatic inoculation** (gardening injury) and the **dimorphic nature** of the fungus. *Sporothrix schenckii* is a thermally dimorphic fungus. In the environment (or at 25°C), it grows as a mold with septate hyphae and "rosette-like" conidia. However, in the body (or at 37°C on enriched media), it converts into a **yeast phase**, which appears as **moist, creamy, white-to-beige colonies** on culture. **Analysis of Incorrect Options:** * **A. Blastomyces:** While also dimorphic, *Blastomyces dermatitidis* typically presents with pulmonary symptoms or systemic dissemination. It is endemic to North America (Ohio/Mississippi River valleys) and is not specifically associated with gardening-related thumb ulcers in the Indian context. * **B. Phaeohyphomycosis:** This refers to infections caused by pigmented (dematiaceous) fungi. These would typically produce dark brown or black colonies due to melanin production, not "creamy" colonies. * **C. Rhinosporidium:** *Rhinosporidium seeberi* causes friable, strawberry-like nasal polyps. Crucially, it **cannot be cultured** on artificial media; diagnosis relies on identifying sporangia in histopathology. **NEET-PG High-Yield Pearls:** * **Clinical Pattern:** Often follows a **lymphocutaneous distribution** (nodules/ulcers ascending along lymphatic channels). * **Morphology:** In tissue, it shows **"Cigar-shaped" bodies**. * **Asteroid Bodies:** Represent the Splendore-Hoeppli phenomenon (eosinophilic material surrounding the yeast). * **Drug of Choice:** **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. * **Culture:** At 25°C, colonies turn from creamy to **dark brown/black** over time (leathery appearance).

Question 63: Smear of vaginal discharge shows budding yeast cells. What is the causative agent?

A. Candida (Correct Answer)
B. Trichomonas
C. Mobiluncus
D. Chlamydia

Explanation: **Explanation:** The presence of **budding yeast cells** (with or without pseudohyphae) in a vaginal discharge smear is the classic microbiological hallmark of **Vulvovaginal Candidiasis (VVC)**. 1. **Why Candida is correct:** *Candida albicans* is a dimorphic fungus that exists as oval, Gram-positive budding yeast cells (blastospores). In a wet mount or Gram stain of vaginal discharge, these yeast cells are diagnostic. Clinically, this presents as a thick, white, "curd-like" or "cottage cheese" discharge with significant pruritus and a normal vaginal pH (<4.5). 2. **Why the other options are incorrect:** * **Trichomonas vaginalis:** A flagellated protozoan. Diagnosis is made by observing **motile, pear-shaped trophozoites** on a wet mount. It causes a greenish-yellow, frothy discharge. * **Mobiluncus:** An anaerobic, Gram-variable, curved rod associated with **Bacterial Vaginosis (BV)**. BV is characterized by "Clue cells" (epithelial cells covered in bacteria) and a fishy odor (positive Whiff test), not yeast cells. * **Chlamydia trachomatis:** An obligate intracellular bacterium. It cannot be seen on a standard light microscope smear and typically causes mucopurulent cervicitis rather than primary vaginitis. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** The specific gold standard for identifying *C. albicans*. * **Culture:** Sabouraud Dextrose Agar (SDA) is the standard medium; colonies appear creamy white with a "yeasty" odor. * **Risk Factors:** Diabetes mellitus, pregnancy, and prolonged antibiotic use are common triggers for VVC. * **Treatment:** Topical clotrimazole or a single dose of oral Fluconazole (150 mg).

Question 64: Black dot ringworm is caused by which of the following?

A. Microsporum
B. Trichophyton (Correct Answer)
C. Epidermophyton
D. Candida

Explanation: **Explanation:** **Black dot ringworm** is a clinical presentation of **Tinea capitis** characterized by small, black, soot-like dots on the scalp. This occurs due to **endothrix infection**, where the fungus grows inside the hair shaft, making it brittle. The hair breaks off flush at the scalp surface, leaving the distal portion of the hair follicle plugged with debris and fungal spores. 1. **Why Trichophyton is correct:** The most common causes of black dot Tinea capitis are **Trichophyton tonsurans** and **Trichophyton violaceum**. These species are "endothrix" (infecting the inside of the hair shaft). Because the hair shaft is weakened internally, it snaps at the skin line, creating the "black dot" appearance. 2. **Why other options are incorrect:** * **Microsporum:** Generally causes **ectothrix** infections (spores on the outside of the hair shaft). This typically results in "Grey patch" Tinea capitis, where the hair breaks further away from the scalp, and the area appears scaly and dull. * **Epidermophyton:** This genus primarily affects the skin (Tinea cruris/pedis) and nails. Crucially, **Epidermophyton does not infect hair.** * **Candida:** While it causes various mucocutaneous infections (like oral thrush or intertrigo), it is not a dermatophyte and does not cause the specific clinical pattern of ringworm or black dot alopecia. **High-Yield Clinical Pearls for NEET-PG:** * **Endothrix (Black Dot):** *T. tonsurans* (most common worldwide), *T. violaceum*. These do **not** fluoresce under Wood’s lamp. * **Ectothrix (Grey Patch):** *Microsporum audouinii*, *M. canis*. These **do** fluoresce (bright green) under Wood’s lamp. * **Favus:** Caused by *T. schoenleinii*; characterized by **scutula** (crusts) and permanent scarring alopecia. * **Drug of Choice:** Oral **Griseofulvin** remains the gold standard for Tinea capitis, though Terbinafine is also frequently used.

Question 65: Spherule is a characteristic feature of which of the following fungi?

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

Explanation: **Explanation:** The correct answer is **Coccidioides** (Option B). **Why Coccidioides is correct:** *Coccidioides immitis* and *C. posadasii* are dimorphic fungi. Unlike most other dimorphic fungi that exist as yeasts in tissue, *Coccidioides* exists as a **spherule** (20–100 µm) in the host's body. These thick-walled spherules are filled with hundreds of small **endospores**. When a spherule ruptures, the endospores are released, and each can potentially develop into a new spherule. This is a classic high-yield histopathological finding. **Why the other options are incorrect:** * **Blastomyces:** Characterized by large, thick-walled yeast cells with **broad-based budding**. * **Histoplasma:** Characterized by small, oval yeast cells typically found **intracellularly** within macrophages. * **Paracoccidioides:** Characterized by large yeast cells with multiple buds, often described as a **"Pilot’s wheel"** or "Mickey Mouse" appearance. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Found in arid/desert soil (Southwestern USA, Mexico). * **Infective form:** Arthroconidia (inhaled from dust). * **Clinical Presentation:** Often presents as "Valley Fever" (fever, arthralgia, and erythema nodosum). * **Diagnosis:** Identification of spherules in sputum, pus, or biopsy is definitive. * **Culture:** On Sabouraud Dextrose Agar (SDA), it grows as a mold with barrel-shaped arthroconidia (highly infectious; must be handled in a Biosafety Level 3 lab).

Question 66: The granules discharged in mycetoma contain which of the following?

A. Bone spicules
B. Fungal colonies (Correct Answer)
C. Pus cells
D. Inflammatory cells

Explanation: **Explanation:** The hallmark of **Mycetoma** (Madura foot) is the triad of localized swelling, multiple interconnecting sinus tracts, and the discharge of **granules**. These granules are not merely debris; they are organized, compact **micro-colonies of the causative agent** (either fungi in eumycetoma or filamentous bacteria in actinomycetoma) embedded in a matrix. * **Why Option B is correct:** In eumycetoma, the granules represent dense aggregates of fungal hyphae. The color, size, and consistency of these granules provide a diagnostic clue to the specific species (e.g., black granules in *Madurella mycetomatis*). * **Why Options C and D are incorrect:** While pus cells (neutrophils) and inflammatory cells (lymphocytes, plasma cells, and giant cells) are present in the surrounding tissue and the discharge as part of the host's immune response, they do not constitute the "granule" itself. The granule is the pathogen's structural form within the lesion. * **Why Option A is incorrect:** Although chronic mycetoma can lead to underlying bone destruction (osteomyelitis) with a "moth-eaten" appearance on X-ray, bone spicules are not typically discharged in the sinus fluid. **High-Yield Clinical Pearls for NEET-PG:** 1. **Eumycetoma:** Caused by fungi; granules are usually large and can be black or white. 2. **Actinomycetoma:** Caused by aerobic actinomycetes (e.g., *Nocardia*, *Actinomadura*); granules are usually smaller and white, yellow, or red. 3. **Diagnosis:** Direct microscopy of the granule (KOH mount) reveals the morphology of the agent. 4. **GMS/PAS Stains:** Best for visualizing fungal hyphae within the granules.

Question 67: Which of the following is a dimorphic fungus?

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

Explanation: **Explanation:** **1. Why Histoplasma is correct:** Dimorphic fungi are characterized by their ability to exist in two distinct morphological forms depending on environmental conditions (primarily temperature). They exist as **molds (hyphae)** in the environment/soil at 25°C and as **yeasts** within the human host at 37°C. *Histoplasma capsulatum* is a classic example of a systemic dimorphic fungus. It is typically found in soil enriched with bird or bat droppings and causes Histoplasmosis, often presenting as a granulomatous lung disease. **2. Why the other options are incorrect:** * **Candida:** While *Candida albicans* is often called "polymorphic" because it forms yeast, pseudohyphae, and true hyphae, it is **not** classified as a classical dimorphic fungus. In fact, it follows the opposite pattern: it exists as yeast at room temperature and forms germ tubes/hyphae at body temperature (37°C). * **Rhizopus and Mucor:** These belong to the class Zygomycetes (Mucormycetes). They are **monomorphic molds** characterized by broad, non-septate, ribbon-like hyphae with right-angle branching. They do not have a yeast phase. **3. NEET-PG High-Yield Pearls:** * **Mnemonic for Dimorphic Fungi:** "**B**ody **C**aptain **H**as **P**robably **S**hot **M**any" (**B**lastomyces, **C**occidioides, **H**istoplasma, **P**aracoccidioides, **S**porothrix, **M**arnerffei/Talaromyces). * **Histoplasma Key Feature:** It is an **intracellular** fungus, typically seen inside macrophages on Giemsa or Wright stain. * **Coccidioides Exception:** It is dimorphic but exists as a **spherule** (not yeast) in the tissue phase at 37°C. * **Talaromyces (Penicillium) marneffei:** The only dimorphic species in its genus; it produces a characteristic red pigment.

Question 68: All of the following are true about mucormycosis, except:

A. Lymphatic invasion
B. Angioinvasion
C. Long-term deferoxamine therapy (Correct Answer)
D. Septate hyphae

Explanation: **Explanation:** Mucormycosis is a life-threatening opportunistic infection caused by fungi of the order Mucorales (e.g., *Rhizopus*, *Mucor*). **Why Option D is the correct answer (The "Except"):** Mucorales are characterized by **broad, ribbon-like, aseptate (or sparsely septate)** hyphae that branch at **right angles (90°)**. In contrast, septate hyphae with acute-angle branching (45°) are characteristic of *Aspergillus*. **Analysis of other options:** * **Angioinvasion (Option B):** This is a hallmark of Mucormycosis. The fungi invade blood vessel walls, leading to thrombosis, tissue ischemia, and the characteristic black necrotic eschar. * **Long-term Deferoxamine Therapy (Option C):** This is a known risk factor. *Rhizopus* uses deferoxamine as a **siderophore** to scavenge iron for its growth. (Note: Newer iron chelators like Deferasirox do not increase this risk). * **Lymphatic Invasion (Option A):** While angioinvasion is more prominent, the fungus can spread via lymphatics and direct tissue extension. **NEET-PG High-Yield Pearls:** 1. **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Ketoacidosis** due to increased free iron), neutropenia, and corticosteroid use. 2. **Diagnosis:** KOH mount or biopsy showing broad, non-septate hyphae. 3. **Clinical Form:** Rhinocerebral mucormycosis is the most common presentation. 4. **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). Isavuconazole and Posaconazole are alternatives.

Question 69: Tinea capitis is caused by which of the following fungi, except?

A. Epidermophyton (Correct Answer)
B. Microsporum
C. Tinea violaceum
D. Tinea schoenleinii

Explanation: **Explanation:** The correct answer is **Epidermophyton**. Dermatophytosis is caused by three main genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. The key to answering this question lies in understanding the specific tissue tropism of each genus: 1. **Epidermophyton:** This genus (specifically *E. floccosum*) infects only the **skin and nails**. It **never** infects the hair. Therefore, it cannot cause Tinea capitis (infection of the scalp hair). 2. **Microsporum:** This genus infects the **skin and hair**, but rarely the nails. It is a common cause of Tinea capitis, often presenting as ectothrix infections. 3. **Trichophyton:** This genus infects **skin, hair, and nails**. Both *Trichophyton violaceum* and *Trichophyton schoenleinii* (the causative agents in options C and D) are well-known causes of Tinea capitis. **Analysis of Options:** * **Option A (Epidermophyton):** Correct, as it lacks the ability to invade hair follicles. * **Option B (Microsporum):** Incorrect, as it frequently causes hair infections (e.g., *M. audouinii*). * **Option C & D (T. violaceum & T. schoenleinii):** Incorrect, as these are species of *Trichophyton*. *T. violaceum* causes "black dot" Tinea capitis, and *T. schoenleinii* is the primary agent of **Favus**, characterized by scutula formation and permanent alopecia. **High-Yield NEET-PG Pearls:** * **Tissue Tropism Mnemonic:** * *Microsporum*: Hair + Skin (No Nails) * *Epidermophyton*: Skin + Nails (No Hair) * *Trichophyton*: All three (Hair, Skin, Nails) * **Wood’s Lamp:** *Microsporum* species typically fluoresce (bright green), while most *Trichophyton* species (except *T. schoenleinii*) do not. * **Favus:** Caused by *T. schoenleinii*; presents with cup-shaped crusts called **scutula**.

Question 70: What is the most common fungal infection in a neutropenic patient?

A. Candidiasis (Correct Answer)
B. Aspergillosis
C. Histoplasmosis
D. None of the above

Explanation: **Explanation:** In neutropenic patients (absolute neutrophil count <500 cells/mm³), the primary defense mechanism against fungal pathogens is compromised. **Candidiasis** is the most common fungal infection in this population. This is due to the disruption of mucosal barriers (mucositis) caused by chemotherapy and the presence of central venous catheters, which allow *Candida* species—normal commensals of the GI tract and skin—to enter the bloodstream (Candidemia). **Analysis of Options:** * **A. Candidiasis (Correct):** It remains the leading cause of invasive fungal infections in neutropenic patients. *Candida albicans* is the most frequent isolate, though non-albicans species (like *C. tropicalis*) are increasingly common in oncology settings. * **B. Aspergillosis:** This is the most common **invasive mold** infection and the second most common fungal infection overall in neutropenics. It typically presents as Invasive Pulmonary Aspergillosis (IPA) following the inhalation of spores. * **C. Histoplasmosis:** This is an endemic dimorphic fungus. While it can cause disseminated disease in immunocompromised hosts, it is geographically restricted and far less common than opportunistic infections like Candidiasis. **Clinical Pearls for NEET-PG:** * **First-line treatment:** For invasive Candidiasis in neutropenic patients, **Echinocandins** (e.g., Caspofungin) are now preferred over Fluconazole. * **Risk Factor:** Prolonged neutropenia (>10–14 days) significantly increases the risk of shifting from *Candida* to *Aspergillus* infections. * **Diagnostic Marker:** 1,3-beta-D-glucan (BDG) is a cell wall marker for both *Candida* and *Aspergillus*, but **Galactomannan** is specific for *Aspergillus*.

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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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