Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 401: A 50-year-old man presents with multiple abscesses and discharging sinuses on his left foot. X-ray of the foot shows destructive changes in the underlying bone. Which of the following is the most likely causative organism?

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

Explanation: ### Explanation The clinical presentation of multiple abscesses, discharging sinuses, and underlying bone destruction in the foot is characteristic of **Mycetoma** (Madura foot). Mycetoma is a chronic granulomatous infection of the subcutaneous tissue that can be caused by either fungi (**Eumycetoma**) or bacteria (**Actinomycetoma**). **Why Nocardia is the correct answer:** * **Nocardia species** (specifically *N. brasiliensis*) are the most common cause of **Actinomycetoma**. * Actinomycetomas are typically more aggressive than eumycetomas, showing rapid progression, multiple discharging sinuses, and early involvement of the underlying bone (as seen in the X-ray). * Nocardia is a Gram-positive, filamentous, branching bacterium that is **weakly acid-fast** (Modified Ziehl-Neelsen stain positive). **Why other options are incorrect:** * **Sporothrix schenckii:** Causes "Rose gardener’s disease." It typically presents as linear nodules along lymphatic drainage (lymphocutaneous sporotrichosis) rather than a tumefaction with discharging sinuses and bone destruction. * **Histoplasma capsulatum:** A dimorphic fungus that primarily causes pulmonary infection. Disseminated forms affect the reticuloendothelial system (liver, spleen, bone marrow) but do not typically cause localized Madura foot. * **Cryptococcus neoformans:** An encapsulated yeast primarily causing meningitis or pneumonia in immunocompromised patients. It does not present as a chronic discharging sinus tract of the foot. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of Mycetoma:** Tumefaction (swelling), Sinus tracts, and Granules (sulfur-like granules in discharge). * **Eumycetoma (Fungal):** Most common cause is *Madurella mycetomatis*. Granules are usually black or white. * **Actinomycetoma (Bacterial):** Most common cause is *Nocardia* or *Actinomadura*. Granules are usually white, yellow, or red. * **Diagnosis:** Crushing the granules and performing Gram stain/Modified AFB (for Nocardia) or KOH mount (for fungi).

Question 402: Which of the following organisms does not have a non-human reservoir?

A. Salmonella typhi (Correct Answer)
B. Yersinia pestis
C. Escherichia coli
D. Clostridium tetani

Explanation: ### Explanation The core concept tested here is the **reservoir of infection**. A reservoir is the natural habitat (human, animal, or environmental) where an infectious agent lives and multiplies. **1. Why Salmonella typhi is correct:** *Salmonella typhi* and *Salmonella paratyphi* are **obligate human pathogens**. They have no known animal or environmental reservoir. Humans are the only hosts, and transmission occurs via the feco-oral route through contaminated food or water. This unique characteristic makes typhoid fever a candidate for potential eradication, unlike zoonotic diseases. **2. Why the other options are incorrect:** * **Yersinia pestis:** This is the classic example of a **zoonotic** pathogen. Its primary reservoirs are wild rodents (like rats, squirrels, and prairie dogs), and it is transmitted to humans via flea bites. * **Escherichia coli:** While many strains are part of the human normal flora, *E. coli* (especially STEC/EHEC) has significant reservoirs in **cattle** and other ruminants. It can also survive in environmental water sources. * **Clostridium tetani:** This organism has an **environmental reservoir**. It exists as highly resilient spores in **soil** and the intestinal tracts of grazing animals (like horses and cattle), which further contaminate the soil through feces. **Clinical Pearls for NEET-PG:** * **Chronic Carriers:** In *S. typhi*, the **gallbladder** is the most common site of long-term colonization (e.g., the famous case of "Typhoid Mary"). * **Zoonosis:** Diseases with animal reservoirs (like Plague, Rabies, or Brucellosis) are significantly harder to eradicate than human-only diseases (like Smallpox or Polio). * **Vi Antigen:** This capsular polysaccharide is a key virulence factor for *S. typhi* and is used in subunit vaccines.

Question 403: All of the following are true about Candida EXCEPT:

A. Pseudohyphae are seen
B. It produces chlamydospores
C. It is a mould (Correct Answer)
D. It is a non-thermally dimorphic fungus

Explanation: **Explanation:** The correct answer is **C (It is a mould)**. *Candida* species are primarily classified as **yeasts**, not moulds. **1. Why Option C is the correct "Except":** *Candida* is a unicellular fungus (yeast) that reproduces by budding. Unlike moulds, which are multicellular filamentous fungi consisting of true hyphae (e.g., *Aspergillus* or *Rhizopus*), *Candida* exists predominantly in yeast form. While it can form "pseudohyphae," it does not fit the structural definition of a mould. **2. Analysis of Other Options:** * **Option A (Pseudohyphae are seen):** This is **true**. Pseudohyphae are formed when buds fail to detach and elongate, creating a "sausage-link" appearance with distinct constrictions at the septa. (Note: *C. glabrata* is the only medically important species that does *not* form pseudohyphae). * **Option B (Produces chlamydospores):** This is **true**. Under specific conditions (e.g., growth on Cornmeal agar at 25°C), *Candida albicans* and *C. dubliniensis* produce thick-walled, resting spores called chlamydospores. * **Option D (Non-thermally dimorphic):** This is **true**. Unlike "true" dimorphic fungi (like *Histoplasma*) which change form based on temperature (yeast at 37°C, mould at 25°C), *Candida* is **pleomorphic**. It can form yeast, pseudohyphae, and true hyphae (germ tubes) within the same temperature range, often triggered by pH or nutrient changes. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test (Reynolds-Braude Phenomenon):** The definitive rapid diagnostic test for *C. albicans*. * **C. glabrata:** Increasing in incidence; notably lacks pseudohyphae and is often resistant to azoles. * **C. auris:** A multi-drug resistant emerging pathogen causing hospital outbreaks. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white, smooth colonies with a "yeasty" odor.

Question 404: What is the major cause of tinea capitis?

A. M. canis
B. E. floccosum
C. T. rubrum
D. T. schoenlenii (Correct Answer)

Explanation: **Explanation:** **Tinea capitis** is a dermatophyte infection of the scalp hair and skin. The correct answer is **T. schoenleinii** because it is the primary causative agent of **Favus**, a severe and chronic form of tinea capitis characterized by the formation of yellow, cup-shaped crusts called **scutula** and permanent scarring alopecia. In many clinical classifications and historical epidemiological data used in exams, *T. schoenleinii* is highlighted as a major specific cause of the inflammatory favosa variety. **Analysis of Options:** * **T. schoenleinii (Correct):** The classic cause of Favus. It shows an **endothrix** pattern of invasion and is identified by "favic chandeliers" (antler-like hyphae) on microscopy. * **M. canis:** A common cause of zoophilic tinea capitis (ectothrix), often transmitted from cats and dogs, but not the "major" global representative for chronic scalp infections in this context. * **E. floccosum:** This fungus **never infects hair**. It only affects the skin and nails (causing tinea cruris and tinea pedis). Therefore, it cannot cause tinea capitis. * **T. rubrum:** While it is the most common cause of dermatophytosis worldwide (tinea corporis and pedis), it is a **rare** cause of tinea capitis. **NEET-PG High-Yield Pearls:** 1. **Most common cause of Tinea capitis (Worldwide):** *T. tonsurans* (Endothrix). 2. **Favus Triad:** Scutula, scarring alopecia, and "favic chandeliers" on KOH mount. 3. **Wood’s Lamp:** *T. schoenleinii* shows a characteristic **pale green** fluorescence. 4. **Rule of Thumb:** *Epidermophyton* affects Skin + Nails; *Microsporum* affects Skin + Hair; *Trichophyton* affects Skin + Hair + Nails.

Question 405: In mycetoma, which organism produces pink to red granules?

A. Madurella
B. Aspergillus
C. Actinumadura madurae
D. Actinomadura pelletri (Correct Answer)

Explanation: **Explanation:** Mycetoma is a chronic, granulomatous infection of the subcutaneous tissue characterized by a triad of localized swelling, underlying bone destruction, and the discharge of grains (granules) through sinus tracts. The **color and consistency of these granules** are high-yield diagnostic clues for identifying the causative agent. **Why Actinomadura pelletieri is correct:** * **Actinomadura pelletieri** is an aerobic actinomycete (Actinomycetoma) known for producing characteristic **small, firm, pink to red granules**. This is a classic "spotter" for NEET-PG. **Analysis of Incorrect Options:** * **Madurella (e.g., M. mycetomatis):** This is the most common cause of Eumycetoma (fungal). It produces **black granules** (Madura foot). * **Aspergillus:** While it can cause opportunistic infections, it is an uncommon cause of mycetoma. When it does occur, granules are typically **white to yellowish**. * **Actinomadura madurae:** This actinomycete produces **large, cream-colored to white/yellowish granules**, not red. **High-Yield Clinical Pearls for NEET-PG:** 1. **Granule Color Coding:** * **Red:** *Actinomadura pelletieri*. * **Black:** *Madurella mycetomatis*, *Exophiala jeanselmei*. * **Yellow/White:** *Nocardia brasiliensis*, *Actinomadura madurae*, *Streptomyces somaliensis*. 2. **Actinomycetoma vs. Eumycetoma:** Actinomycetoma (bacterial) usually has a more rapid progression and responds to antibiotics (Welsh regimen), whereas Eumycetoma (fungal) is slower and requires surgical debridement plus antifungals. 3. **Diagnosis:** The most definitive diagnosis is made by histopathological examination of the granules using **Gomori Methenamine Silver (GMS)** or **PAS stains**.

Question 406: Which fungus is typically not isolated in standard culture media?

A. Cryptococcus
B. Dermatophyte
C. Candida
D. Pneumocystis jiroveci (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Pneumocystis jiroveci**. **Why it is correct:** *Pneumocystis jiroveci* is an atypical fungus that lacks ergosterol in its cell membrane and cannot be grown on standard fungal culture media (like Sabouraud Dextrose Agar). It is an **obligate extracellular parasite** that requires specific cell culture systems or animal models for growth, which are not used in routine clinical diagnostics. Diagnosis relies primarily on microscopic visualization (using GMS or Periodic acid-Schiff stains) of cysts or trophozoites in bronchoalveolar lavage (BAL) fluid or induced sputum, or via PCR. **Why the other options are incorrect:** * **A. Cryptococcus:** *Cryptococcus neoformans* grows readily on SDA and specialized media like Bird Seed Agar (Niger seed agar), where it produces characteristic brown-pigmented colonies due to phenoloxidase activity. * **B. Dermatophytes:** Fungi such as *Trichophyton*, *Microsporum*, and *Epidermophyton* are routinely isolated on SDA or Dermatophyte Test Medium (DTM), which contains phenol red as a pH indicator. * **C. Candida:** *Candida albicans* and other species are the most common fungi isolated in clinical labs. They grow rapidly (24–48 hours) on SDA and Blood Agar, forming creamy white colonies. **High-Yield Clinical Pearls for NEET-PG:** * **Stains for Pneumocystis:** Gomori Methenamine Silver (GMS) is the gold standard (stains cysts black/brown). * **Treatment of Choice:** Trimethoprim-Sulfamethoxazole (TMP-SMX), not standard antifungals, because it lacks ergosterol. * **CD4 Count:** Infection is typically seen in HIV patients when the CD4 count falls below **200 cells/mm³**. * **Radiology:** Characterized by bilateral "ground-glass opacities" on chest X-ray.

Question 407: Which statement is NOT true about Cryptococcus neoformans?

A. Grows at 37°C
B. Grows on Sabouraud's agar
C. Has a polysaccharide capsule
D. Is urease negative (Correct Answer)

Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated opportunistic yeast that is a frequent cause of meningitis, especially in immunocompromised patients (e.g., HIV/AIDS). **Why Option D is the correct answer:** *Cryptococcus neoformans* is **Urease positive**. This is a key biochemical characteristic used for its identification in the laboratory. The enzyme urease hydrolyzes urea into ammonia and carbon dioxide, increasing the pH and turning Christensen’s urea agar pink. Therefore, the statement "Is urease negative" is incorrect. **Analysis of other options:** * **Option A (Grows at 37°C):** Unlike many saprophytic fungi, *C. neoformans* is thermotolerant and grows well at 37°C. This ability to grow at human body temperature is a vital virulence factor. * **Option B (Grows on Sabouraud's agar):** It grows readily on Sabouraud Dextrose Agar (SDA), typically forming cream-colored, mucoid colonies (due to the capsule) within 48–72 hours. * **Option C (Has a polysaccharide capsule):** This is the most defining feature of *Cryptococcus*. The thick glucuronoxylomannan capsule is antiphagocytic and is visualized using **India Ink** (negative staining), where it appears as a clear halo against a dark background. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **Latex Agglutination test** for capsular antigen is more sensitive than India Ink. * **Culture:** On **Niger Seed Agar** (Birdseed agar), it produces brown/black colonies due to phenoloxidase activity (melanin production). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Question 408: Aflatoxin is produced by which fungus?

A. Aspergillus flavus (Correct Answer)
B. Aspergillus fumigatus
C. Aspergillus niger
D. Penicillium marneffei

Explanation: ### Explanation **Correct Option: A. Aspergillus flavus** Aflatoxins are potent mycotoxins produced primarily by **Aspergillus flavus** and *Aspergillus parasiticus*. These fungi commonly contaminate stored agricultural crops like groundnuts (peanuts), maize, and rice under warm, humid conditions. **Medical Concept:** Aflatoxin B1 is the most potent natural carcinogen known. It undergoes metabolic activation in the liver to form an epoxide, which binds to DNA and causes a mutation in the **p53 tumor suppressor gene** (specifically a G to T transversion at codon 249). This significantly increases the risk of **Hepatocellular Carcinoma (HCC)**, especially in patients with chronic Hepatitis B infection. **Why other options are incorrect:** * **B. Aspergillus fumigatus:** This is the most common cause of invasive Aspergillosis, Aspergilloma (fungus ball), and Allergic Bronchopulmonary Aspergillosis (ABPA). It does not produce aflatoxins. * **C. Aspergillus niger:** Known for causing Otomycosis (fungal ear infection) and producing citric acid commercially. It is characterized by black-colored conidia but is not a source of aflatoxin. * **D. Penicillium marneffei (Talaromyces marneffei):** A dimorphic fungus prevalent in Southeast Asia, typically causing systemic infections in HIV-positive patients. It does not produce aflatoxins. **High-Yield Clinical Pearls for NEET-PG:** * **Target Organ:** Liver (Hepatotoxicity and Carcinogenicity). * **Detection:** Aflatoxins exhibit **fluorescence** under UV light (B1 and B2 fluoresce blue; G1 and G2 fluoresce green). * **Acute Toxicity:** Can lead to acute hepatic failure, presenting with jaundice and portal hypertension. * **Synergy:** There is a synergistic effect between Aflatoxin exposure and **Hepatitis B Virus (HBV)** in the pathogenesis of liver cancer.

Question 409: A HIV positive patient presents with cough for 10 days. Sputum culture by SDA reveals broad budding yeast. What is the diagnosis?

A. Histoplasma capsulatum
B. Blastomycosis (Correct Answer)
C. Coccidiodomycosis
D. Paracoccidiomycosis

Explanation: **Explanation:** The diagnosis is **Blastomycosis**, caused by the dimorphic fungus *Blastomyces dermatitidis*. The key diagnostic feature mentioned in the question is the presence of **broad-based budding yeast** (the daughter cell is attached to the parent cell by a wide neck). **Why Blastomycosis is correct:** In tissue or culture at 37°C (SDA), *Blastomyces* appears as large, thick-walled, spherical yeast cells. The characteristic "broad base" attachment between the bud and the parent cell is pathognomonic. It typically presents as a pulmonary infection (cough, fever) and is an opportunistic infection in immunocompromised individuals, such as HIV-positive patients. **Why other options are incorrect:** * **Histoplasma capsulatum:** Characterized by **small, intracellular yeast** cells (found within macrophages) with narrow-based budding. It does not show broad-based buds. * **Coccidioidomycosis:** Characterized by **spherules containing endospores** in tissue samples, not budding yeast. * **Paracoccidioidomycosis:** Characterized by large yeast cells with multiple buds, often described as a **"Pilot’s wheel"** or "Mickey Mouse" appearance, rather than a single broad-based bud. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Blastomyces:** **B**lasto = **B**ig, **B**lue, **B**road-**B**ased **B**uds. * **Geographic distribution:** Often associated with the Ohio and Mississippi River valleys (similar to Histoplasma). * **Systemic involvement:** In disseminated cases, it frequently involves the **skin** (verrucous lesions) and **bones**. * **Staining:** Best visualized using Silver stains (GMS) or PAS stain.

Question 410: A 20-year-old man presents with swelling of the left lower limb and hydrocele. Which of the following is NOT a causative agent for these symptoms?

A. Brugia malayi
B. Brugia timori
C. Wuchereria bancrofti
D. Onchocerca volvulus (Correct Answer)

Explanation: ### **Explanation** The clinical presentation of lower limb swelling (elephantiasis) and hydrocele is characteristic of **Lymphatic Filariasis**. This condition is caused by filarial nematodes that reside in the lymphatic system, leading to chronic lymphadenitis and lymphatic obstruction. **1. Why Onchocerca volvulus is the correct answer:** *Onchocerca volvulus* is the causative agent of **Onchocerciasis (River Blindness)**. Unlike the other options, it does not inhabit the lymphatic vessels. Instead, the adult worms reside in subcutaneous nodules, and the microfilariae migrate primarily through the **skin and eyes**. Clinical features include dermatitis, subcutaneous nodules (onchocercomata), and ocular lesions leading to blindness. It does not typically cause hydrocele or lower limb elephantiasis. **2. Analysis of Incorrect Options:** * **Wuchereria bancrofti:** Responsible for ~90% of lymphatic filariasis cases worldwide. It has a predilection for the lymphatics of the inguinal region and male genitalia, frequently causing **hydrocele**, scrotal elephantiasis, and chyluria. * **Brugia malayi & Brugia timori:** These species cause "Brugian Filariasis." While they cause lower limb elephantiasis, they **rarely involve the genitalia** (hydrocele is uncommon compared to *W. bancrofti*). However, they are still recognized causative agents of the lymphatic symptoms described. **3. Clinical Pearls for NEET-PG:** * **Vector:** *W. bancrofti* is primarily transmitted by the *Culex* mosquito; *Onchocerca* is transmitted by the **Blackfly (*Simulium*)**. * **Diagnosis:** The gold standard for lymphatic filariasis is the detection of microfilariae in a **peripheral blood smear** (collected at night due to nocturnal periodicity). * **Drug of Choice:** **Diethylcarbamazine (DEC)** is used for lymphatic filariasis; **Ivermectin** is the drug of choice for *Onchocerca volvulus*. * **Mazzotti Reaction:** A severe immune response seen during the treatment of Onchocerciasis with diethylcarbamazine.

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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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