Mycology — MCQs

A 31-year-old HIV-positive man develops a severe pneumonia. Lower respiratory tract secretions obtained by fiberoptic bronchoscopy with bronchoalveolar lavage and stained with methenamine silver stain demonstrate cup-shaped cysts with sharply outlined walls. Which of the following organisms is the most likely pathogen in this case?

Q308Easy

Sclerotic bodies are seen in which of the following conditions?

Q309Easy

Dermatophytes infect which of the following?

Q310Medium

Which of the following dermatophytes is spread from animals to humans?

Mycology Indian Medical PG Practice Questions and MCQs

Question 301: Cryptococcus neoformans is classified as which type of microorganism?

A. Protozoa
B. Fungus (Correct Answer)
C. Parasite
D. Mycoplasma

Explanation: **Explanation:** **Cryptococcus neoformans** is a classic example of an **encapsulated yeast**, belonging to the kingdom **Fungi**. It is medically significant as an opportunistic pathogen that primarily causes meningitis and pneumonia in immunocompromised individuals (e.g., HIV/AIDS patients). **Why the correct answer is right:** * **Fungus:** *C. neoformans* is a monomorphic yeast (not dimorphic) that reproduces by narrow-based budding. Its defining mycological feature is a thick **polysaccharide capsule** (composed of glucuronoxylomannan), which serves as its primary virulence factor by inhibiting phagocytosis. **Why the incorrect options are wrong:** * **Protozoa:** These are unicellular eukaryotic organisms (like *Plasmodium* or *Amoeba*) that lack a chitinous cell wall, which fungi possess. * **Parasite:** While fungi can be parasitic, "Parasite" in medical microbiology typically refers to protozoa or helminths (worms). * **Mycoplasma:** These are the smallest free-living bacteria. They are prokaryotic and uniquely lack a cell wall, whereas *Cryptococcus* is a eukaryotic organism with a complex cell wall. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Staining:** Demonstrated by **India Ink** (shows a clear halo against a dark background) or **Mucicarmine** (stains the capsule red). * **Antigen Detection:** **CrAg (Cryptococcal Antigen)** lateral flow assay is the most sensitive screening test. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy, mucoid colonies. It is **urease positive**. * **Histopathology:** Shows "Soap bubble appearance" in the brain parenchyma.

Question 302: Ergotism is due to toxic alkaloids produced by which fungus?

A. Claviceps purpurea (Correct Answer)
B. Trichophyton
C. Fusarium species
D. Absidia

Explanation: **Explanation:** **Claviceps purpurea** is the correct answer because it is the primary fungal agent responsible for **Ergotism** (St. Anthony’s Fire). This fungus infects cereal grains, particularly rye. It replaces the grain with a dark, hardened fungal mass called a **sclerotium**, which contains potent toxic alkaloids (e.g., ergotamine, ergometrine). When ingested, these alkaloids cause intense vasoconstriction and neurological symptoms. **Analysis of Incorrect Options:** * **Trichophyton:** This is a dermatophyte responsible for superficial fungal infections of the skin, hair, and nails (Tinea/Ringworm). It does not produce systemic toxins like ergot alkaloids. * **Fusarium species:** While some species produce mycotoxins (like T-2 toxin or fumonisins), they are primarily known for causing keratitis, onychomycosis, or disseminated infections in immunocompromised patients. * **Absidia (Lichtheimia):** This is a member of the Mucorales order. It causes **Mucormycosis**, an invasive angio-destructive infection, typically in patients with uncontrolled diabetes or neutropenia. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation of Ergotism:** 1. **Gangrenous:** Severe vasoconstriction leading to "dry gangrene" of the extremities. 2. **Convulsive:** Neurological symptoms including hallucinations, seizures, and muscle spasms. * **Pharmacology Link:** Ergot derivatives are used clinically in the treatment of **migraines** (Ergotamine) and **postpartum hemorrhage** (Ergometrine) due to their vasoconstrictive and oxytocic properties. * **LSD Connection:** Lysergic acid diethylamide (LSD) is a synthetic derivative of lysergic acid found in ergot.

Question 303: Which of the following statements regarding mycetoma is FALSE?

A. Mycetoma is a neglected tropical disease.
B. Eumycetoma has no acceptable treatment at present.
C. Actinomycetoma is treated with courses of antibiotics, which usually include co-trimoxazole and amikacin.
D. Recurrence in patients with Eumycetoma is uncommon. (Correct Answer)

Explanation: ### Explanation **Mycetoma** is a chronic, granulomatous, and debilitating inflammatory disease of the skin and subcutaneous tissues, characterized by a triad of **painless swelling, sinus tracts, and discharge of grains.** **Why Option D is the Correct Answer (The False Statement):** Recurrence in **Eumycetoma** (caused by fungi) is actually **very common**. Unlike Actinomycetoma, Eumycetoma is often poorly encapsulated, making surgical excision difficult. Even with long-term antifungal therapy (like Itraconazole), the cure rate is low (approx. 25-35%), and the risk of recurrence remains high, often necessitating repeated surgeries or amputation. **Analysis of Other Options:** * **Option A:** Mycetoma was officially recognized by the WHO as a **Neglected Tropical Disease (NTD)** in 2016 due to its prevalence in the "Mycetoma Belt" and the lack of diagnostic/therapeutic resources. * **Option B:** While antifungals exist, there is currently **no "gold standard" or highly effective medical treatment** for Eumycetoma. Most cases require a combination of long-term medication and aggressive surgery, yet outcomes remain suboptimal. * **Option C:** **Actinomycetoma** (caused by bacteria like *Nocardia*) responds well to medical therapy. The **Welsh Regime** (Amikacin + Co-trimoxazole) is the standard treatment and has a high success rate. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** Most common cause of Eumycetoma worldwide is *Madurella mycetomatis*. * **Grains:** Black grains are pathognomonic for Eumycetoma; Yellow/White grains can be seen in both, but Red grains are specific to *Actinomadura pelletieri*. * **Diagnosis:** "Dot-in-a-circle" sign on MRI/Ultrasound is a characteristic feature. * **Site:** The foot is the most common site (Madura Foot), usually following traumatic inoculation (e.g., thorn prick).

Question 304: A young man presents with hepatocellular carcinoma and has a history of consuming soy sauce, which may have been contaminated. Which organism is likely responsible for the aflatoxin exposure?

A. Fusarium
B. Rhizopus
C. Candida
D. Aspergillus (Correct Answer)

Explanation: **Explanation:** The correct answer is **Aspergillus**. This question tests the association between specific fungal toxins and clinical pathology. **1. Why Aspergillus is correct:** Aflatoxins are potent hepatocarcinogens produced primarily by **Aspergillus flavus** and **Aspergillus parasiticus** [1]. These fungi commonly contaminate stored agricultural products such as peanuts, maize, rice, and soy. Chronic ingestion of aflatoxin leads to a mutation in the **p53 tumor suppressor gene** (specifically a G to T transversion at codon 249), which significantly increases the risk of developing **Hepatocellular Carcinoma (HCC)** [2]. In many Asian cultures, fermented soy products like soy sauce are a documented source of exposure if the fermentation process is contaminated. **2. Why the other options are incorrect:** * **Fusarium:** Known for producing **Fumonisins** (linked to esophageal cancer) and **T-2 toxins** (Alimentary Toxic Aleukia). It does not produce aflatoxins. * **Rhizopus:** A member of the Mucormycetes family, it causes **Mucormycosis** (rhinocerebral infections), especially in diabetic patients. It is not associated with mycotoxin-induced malignancy. * **Candida:** An opportunistic yeast responsible for oral thrush, vaginal candidiasis, and systemic fungemia. It does not produce carcinogenic toxins. * **Other Mycotoxins to remember:** *Ochratoxin* (Aspergillus/Penicillium) causes nephrotoxicity; *Ergot alkaloids* (Claviceps purpurea) cause St. Anthony’s Fire (vasoconstriction/gangrene). **3. NEET-PG High-Yield Pearls:** * **Aflatoxin B1** is the most potent and most common metabolite associated with HCC. * **Synergy:** The risk of HCC increases exponentially if a patient has both chronic **Hepatitis B (HBV)** infection and aflatoxin exposure. * **Diagnosis:** Aflatoxin exposure can be monitored via biomarkers in urine or aflatoxin-albumin adducts in the blood. [2]

Question 305: Which of the following fungi cannot be cultured?

A. Candida
B. Pneumocystis (Correct Answer)
C. Malassezia
D. Blastomyces

Explanation: ### Explanation **Pneumocystis jirovecii** (formerly *P. carinii*) is the correct answer because it is an **obligate extracellular parasite** that lacks the metabolic pathways required for growth on standard synthetic laboratory media. Unlike most fungi, it cannot be cultured *in vitro*. Diagnosis relies heavily on microscopic visualization (using GMS or Giemsa stains) of respiratory specimens or molecular methods like PCR. **Analysis of Incorrect Options:** * **Candida:** Readily grows on standard media like Sabouraud Dextrose Agar (SDA) and Blood Agar, typically forming smooth, cream-colored colonies within 24–48 hours. * **Malassezia:** While fastidious, most species (except *M. pachydermatis*) can be cultured by supplementing media with **long-chain fatty acids** (e.g., overlaying SDA with sterile olive oil), as they are lipophilic. * **Blastomyces:** As a dimorphic fungus, it can be cultured at 25°C (mold form) and 37°C (yeast form) on enriched media like Brain Heart Infusion (BHI) agar. **High-Yield Clinical Pearls for NEET-PG:** * **Taxonomy:** Once classified as a protozoan, *Pneumocystis* is now classified as a fungus based on nucleic acid analysis, though its cell membrane contains **cholesterol** instead of ergosterol (making it inherently resistant to Amphotericin B and Azoles). * **Drug of Choice:** Trimethoprim-Sulfamethoxazole (TMP-SMX). * **Staining:** **Gomori Methenamine Silver (GMS)** is the gold standard for visualizing "crushed ping-pong ball" shaped cysts. * **CD4 Count:** Typically causes pneumonia (PCP) in HIV patients when the CD4 count falls below **200 cells/µL**.

Question 306: The diagnostic feature of phaeohyphomycosis is the presence of:

A. Brownish spherical sclerotic bodies
B. Brownish septate hyphae within the lesions (Correct Answer)
C. Hard granules composed of hyphae
D. Conversion from hyphal growth to yeast cells in the host

Explanation: **Explanation:** **Phaeohyphomycosis** is a clinical syndrome caused by a diverse group of dematiaceous (pigmented) fungi. The defining characteristic of these fungi is the presence of **melanin** in their cell walls, which gives them a natural brown or black color. 1. **Why Option B is correct:** In phaeohyphomycosis, the fungi exist in the host tissue as **brown-pigmented, septate hyphae**, pseudohyphae, or yeast-like cells. Unlike other fungal infections, these do not form organized granules or specific bodies; the diagnosis is confirmed by observing these naturally pigmented hyphal elements in histopathological sections (H&E stain). 2. **Why other options are incorrect:** * **Option A (Sclerotic bodies):** These are thick-walled, copper-colored, rounded structures (also called Medlar bodies or Muriform bodies) diagnostic of **Chromoblastomycosis**, not phaeohyphomycosis. * **Option C (Hard granules):** These are characteristic of **Mycetoma** (Eumycetoma), where hyphae are organized into compact grains or colonies. * **Option D (Dimorphism):** This refers to **Systemic Mycoses** (e.g., Histoplasmosis, Blastomycosis) where the fungus shifts from mold in the environment to yeast in the host. Phaeohyphomycotic fungi are generally monomorphic molds. **High-Yield Clinical Pearls for NEET-PG:** * **Causative agents:** Most common is *Exophiala jeanselmei* and *Wangiella dermatitidis*. * **Staining:** While naturally pigmented, **Masson-Fontana stain** (which detects melanin) can be used to confirm the diagnosis. * **Clinical Presentation:** Most commonly presents as a **subcutaneous cystic swelling** (phaeohyphomycotic cyst) following traumatic inoculation. * **Key Distinction:** Remember the "Dematiaceous Trio": 1. **Chromoblastomycosis:** Sclerotic bodies. 2. **Mycetoma:** Grains/Granules. 3. **Phaeohyphomycosis:** Pigmented hyphae.

Question 307: A 31-year-old HIV-positive man develops a severe pneumonia. Lower respiratory tract secretions obtained by fiberoptic bronchoscopy with bronchoalveolar lavage and stained with methenamine silver stain demonstrate cup-shaped cysts with sharply outlined walls. Which of the following organisms is the most likely pathogen in this case?

A. Candida albicans
B. Giardia lamblia
C. Haemophilus influenzae
D. Pneumocystis jirovecii (Correct Answer)

Explanation: **Explanation:** The clinical presentation and laboratory findings are classic for **Pneumocystis Pneumonia (PCP)**, caused by *Pneumocystis jirovecii*. **1. Why the Correct Answer is Right:** *Pneumocystis jirovecii* is an opportunistic fungus and the most common opportunistic infection in HIV patients with a **CD4 count <200 cells/mm³**. The pathognomonic finding on **Gomori Methenamine Silver (GMS) stain** is the presence of **cup-shaped or crushed ping-pong ball-shaped cysts** (5–8 µm) with dark, eccentric thickening (intracystic bodies). Bronchoalveolar lavage (BAL) is the gold-standard diagnostic procedure due to its high sensitivity. **2. Why Incorrect Options are Wrong:** * **A. Candida albicans:** While common in HIV, it typically causes oral thrush or esophagitis. On silver stain, it shows budding yeasts and **pseudohyphae**, not cup-shaped cysts. * **B. Giardia lamblia:** This is an intestinal protozoan causing malabsorptive diarrhea. It is not a respiratory pathogen and would be identified in stool samples as pear-shaped trophozoites. * **C. Haemophilus influenzae:** This is a gram-negative coccobacillus. It causes bacterial pneumonia (lobar consolidation) and would be visualized on a Gram stain, not a silver stain. **3. High-Yield Clinical Pearls for NEET-PG:** * **Chest X-ray:** Characteristically shows bilateral, symmetrical **perihilar "ground-glass" opacities**. * **Laboratory:** Elevated **Serum LDH** levels are a sensitive but non-specific marker for PCP. * **Stains:** Besides GMS, **Toluidine blue O** also stains cysts; **Giemsa/Wright stain** is used for trophic forms. * **Treatment:** The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if PaO₂ <70 mmHg or A-a gradient >35 mmHg.

Question 308: Sclerotic bodies are seen in which of the following conditions?

A. Histoplasmosis
B. Chromoblastomycosis (Correct Answer)
C. Coccidomycosis
D. Rhinosporidiosis

Explanation: **Explanation:** **Chromoblastomycosis** is a chronic fungal infection of the skin and subcutaneous tissue caused by dematiaceous (pigmented) fungi like *Phialophora verrucosa* and *Fonsecaea pedrosoi*. The hallmark histological feature of this condition is the presence of **Sclerotic bodies** (also known as **Medlar bodies**, **Muriform bodies**, or **Copper-penny bodies**). These are thick-walled, dark brown, globe-shaped fungal cells that divide by binary fission (septation) rather than budding. They represent a diagnostic stage found within granulomas or abscesses in the tissue. **Analysis of Incorrect Options:** * **Histoplasmosis:** Characterized by small, oval, intracellular yeast cells (2–4 µm) typically found within macrophages. It does not form sclerotic bodies. * **Coccidioidomycosis:** Identified by the presence of large, thick-walled **spherules** (20–100 µm) filled with numerous endospores. * **Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it is characterized by massive **sporangia** (up to 350 µm) containing thousands of spores, usually presenting as friable nasal polyps. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Chromoblastomycosis typically presents as "cauliflower-like" verrucous (warty) lesions, usually on the lower limbs of barefoot workers. * **Pigmentation:** The dark color of sclerotic bodies is due to **melanin** in the fungal cell wall. * **Diagnostic Clue:** If a question mentions "Copper-penny bodies" or "binary fission in tissue," always think of Chromoblastomycosis. * **Treatment:** It is notoriously difficult to treat; Itraconazole and Terbinafine are commonly used, often combined with cryotherapy.

Question 309: Dermatophytes infect which of the following?

A. Subcutaneous tissue
B. Systemic organs
C. Nails, hair and skin (Correct Answer)
D. Superficial skin and deep tissue

Explanation: **Explanation:** **Dermatophytes** are a group of closely related filamentous fungi that cause infections known as **Tinea** or **Ringworm**. The correct answer is **Nails, hair, and skin** because these fungi are **keratinophilic**—they possess the enzyme **keratinase**, which allows them to metabolize and live on keratinized tissues. Since keratin is only found in the non-living cornified layers of the skin (epidermis), hair, and nails, the infection remains restricted to these areas. **Analysis of Incorrect Options:** * **A & D (Subcutaneous and Deep tissue):** Dermatophytes are generally unable to penetrate deeper tissues because they are inhibited by serum factors (like transferrin) and the body’s internal temperature. Subcutaneous infections are typically caused by fungi like *Sporothrix schenckii* or agents of Mycetoma. * **B (Systemic organs):** Systemic infections are caused by dimorphic fungi (e.g., Histoplasma) or opportunistic yeasts (e.g., Candida), which can survive at 37°C and disseminate via the bloodstream. **High-Yield NEET-PG Pearls:** 1. **Three Genera:** *Trichophyton* (infects hair, skin, and nails), *Microsporum* (hair and skin), and *Epidermophyton* (skin and nails). 2. **Wood’s Lamp:** Used for diagnosis; *Microsporum* species typically show a bright green fluorescence. 3. **Culture:** Sabouraud Dextrose Agar (SDA) is the standard medium. 4. **Ectothrix vs. Endothrix:** Refers to whether fungal spores are outside or inside the hair shaft; *T. tonsurans* is a classic cause of endothrix infection (Black dot tinea capitis).

Question 310: Which of the following dermatophytes is spread from animals to humans?

A. Trichophyton rubrum
B. Trichophyton tonsurans
C. Trichophyton floccosum
D. Trichophyton verrucosum (Correct Answer)

Explanation: ### Explanation Dermatophytes are classified into three groups based on their primary host and habitat: **Anthropophilic** (humans), **Zoophilic** (animals), and **Geophilic** (soil). Understanding this classification is high-yield for NEET-PG, as it dictates the clinical presentation and source of infection. **Why Option D is Correct:** **Trichophyton verrucosum** is a **zoophilic** dermatophyte. Its primary hosts are cattle. Humans typically acquire the infection through direct contact with infected livestock or contaminated farm equipment. Zoophilic infections in humans often trigger a more intense inflammatory response compared to anthropophilic species, frequently presenting as a **Kerion** (a painful, inflammatory boggy mass on the scalp). **Analysis of Incorrect Options:** * **A. Trichophyton rubrum:** This is the most common **anthropophilic** dermatophyte worldwide. it is the leading cause of Tinea pedis, Tinea cruris, and Onychomycosis. It typically causes chronic, non-inflammatory infections. * **B. Trichophyton tonsurans:** An **anthropophilic** fungus and the leading cause of epidemic Tinea capitis (Endothrix infection) in children. It is spread via human-to-human contact or fomites (combs, hats). * **C. Epidermophyton floccosum:** (Note: Option C lists *Trichophyton floccosum*, but the genus is *Epidermophyton*). It is an **anthropophilic** fungus that affects the skin and nails but **never the hair**. **NEET-PG Clinical Pearls:** * **Zoophilic species:** *T. verrucosum* (cattle), *T. mentagrophytes* (rodents), *Microsporum canis* (cats/dogs). * **Geophilic species:** *Microsporum gypseum* (soil). * **Inflammation Level:** Geophilic/Zoophilic > Anthropophilic. * **Wood’s Lamp:** *M. canis* (Zoophilic) fluoresces bright green, while most *Trichophyton* species (except *T. schoenleinii*) do not.

Practice by Chapter

Classification of Fungi

Practice Questions

Superficial Mycoses

Practice Questions

Dermatophytes

Practice Questions

Subcutaneous Mycoses

Practice Questions

Candidiasis

Practice Questions

Aspergillosis

Practice Questions

Cryptococcosis

Practice Questions

Zygomycosis

Practice Questions

Endemic Mycoses

Practice Questions

Opportunistic Fungal Infections

Practice Questions

Antifungal Agents

Practice Questions

Laboratory Diagnosis of Fungal Infections

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free

Mycology — MCQs

Mycology — MCQs

On this page

Practice by Chapter

Want unlimited practice?