Mycology — MCQs

A 53-year-old woman with end-stage renal disease who received a kidney transplant was maintained on an immunosuppressive regimen. Three months later, she developed a fever (38.3°C) and acute renal failure. Renal transplant biopsy was performed, and Periodic acid-Schiff staining showed yeast cells and hyphae. What is the most likely causative organism for this patient's infection?

Q37Easy

Which of the following is a non-culturable fungus?

Q38Easy

At what angle do Aspergillus hyphae typically branch?

Q39Easy

"Tuberculate spores" are characteristic features of which of the following fungi?

Q40Easy

Germ tubes are formed mainly by which organism?

Mycology Indian Medical PG Practice Questions and MCQs

Question 31: Which of the following statements about mycetoma is false?

A. It can affect the lower and upper extremities.
B. It is caused by actinomycetes and filamentous fungi.
C. Diagnosis is made by examination of pus.
D. It is uncommon in India. (Correct Answer)

Explanation: **Explanation:** **Mycetoma** is a chronic, granulomatous, subcutaneous infection characterized by a clinical triad of localized swelling, multiple interconnecting sinus tracts, and the discharge of grains (sulfur granules). **1. Why Option D is the Correct Answer (The False Statement):** Mycetoma is **not uncommon** in India. In fact, India is part of the global "Mycetoma Belt" (along with Sudan, Mexico, and Venezuela). It is endemic in several Indian states, particularly Rajasthan, Tamil Nadu, and West Bengal. It primarily affects rural laborers and farmers who walk barefoot, leading to traumatic inoculation of the causative agents from the soil. **2. Analysis of Other Options:** * **Option A (True):** While the foot is the most common site ("Madura Foot"), mycetoma can affect any part of the body exposed to trauma, including the hands (upper extremities), back, and shoulders. * **Option B (True):** It is caused by two distinct groups: **Actinomycetoma** (caused by filamentous bacteria like *Nocardia*, *Actinomadura*, and *Streptomyces*) and **Eumycetoma** (caused by true fungi like *Madurella mycetomatis*). * **Option C (True):** Diagnosis relies on the macroscopic and microscopic examination of **grains** discharged from the sinus tracts in the pus. The color, size, and consistency of these grains provide a preliminary identification of the causative agent. **Clinical Pearls for NEET-PG:** * **Actinomycetoma:** Faster progression, more inflammatory, responds to antibiotics (Welsh regimen: Amikacin + Cotrimoxazole). * **Eumycetoma:** Slower progression, well-defined margins, requires surgical debridement and long-term antifungals (Itraconazole). * **Grains:** Black grains are pathognomonic for **Eumycetoma** (*Madurella*). Red grains suggest *Actinomadura pelletieri*. White/Yellow grains can be seen in both types.

Question 32: Cryptococcus neoformans has a significant predilection for which body system?

A. Central nervous system (Correct Answer)
B. Respiratory system
C. Gastrointestinal system
D. Cardiovascular system

Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that primarily enters the body through the respiratory tract via inhalation of basidiospores (often found in pigeon droppings). While the lungs are the portal of entry, the fungus has a unique and significant **neurotropism**, meaning it has a strong predilection for the **Central Nervous System (CNS)**. **Why the CNS is the correct answer:** The predilection for the CNS, specifically causing **Cryptococcal meningitis**, is due to several factors: 1. **Blood-Brain Barrier (BBB) Crossing:** The organism uses a "Trojan horse" mechanism (inside macrophages) or direct transcytosis to cross the BBB. 2. **Nutrient Availability:** The fungus thrives on specific compounds found in the cerebrospinal fluid (CSF), such as **gamma-aminobutyric acid (GABA)** and high concentrations of glucose. 3. **Urease Production:** Its urease enzyme helps in sequestering microvascular sites, facilitating CNS invasion. **Why other options are incorrect:** * **Respiratory System:** While the lungs are the initial site of infection (Primary Pulmonary Cryptococcosis), the infection is often asymptomatic or self-limiting in immunocompetent hosts. Its clinical hallmark and most dangerous manifestation is CNS involvement. * **Gastrointestinal/Cardiovascular Systems:** These are not primary targets for *Cryptococcus*. While disseminated disease can occur in severely immunocompromised patients (e.g., AIDS), these systems are rarely the focal point of the pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **polysaccharide capsule** (Glucuronoxylomannan) is the most important virulence factor, which inhibits phagocytosis. * **Staining:** **India Ink** preparation of CSF shows a "halo" (negative staining) due to the capsule. * **Histopathology:** **Mucicarmine stain** specifically stains the capsule bright red. * **Biochemical Test:** It is **Urease positive** and produces **melanin** on Niger seed (Birdseed) agar. * **Clinical Sign:** In the brain, it can form "soap bubble" lesions (gelatinous pseudocysts) in the basal ganglia.

Question 33: Tinea capitis (endothrix type) is caused by which of the following fungi?

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

Explanation: **Explanation:** Tinea capitis is a fungal infection of the scalp and hair shafts. The classification into **Endothrix** and **Ectothrix** depends on where the arthroconidia (spores) are formed in relation to the hair shaft. **1. Why Trichophyton tonsurans is correct:** In **Endothrix** infections, the fungus grows inside the hair shaft, replacing the internal keratin and leaving the cuticle intact. This makes the hair brittle, causing it to break off at the scalp surface, leading to the classic clinical presentation of **"Black Dot" Tinea Capitis**. *Trichophyton tonsurans* is the most common cause of endothrix infection worldwide. *Trichophyton violaceum* also causes endothrix, but *T. tonsurans* is the primary prototype for this question. **2. Analysis of Incorrect Options:** * **Epidermophyton (A):** This genus primarily infects the skin and nails (Tinea cruris, Tinea pedis). Crucially, **Epidermophyton does not infect hair.** * **Trichophyton violaceum (C):** While it *does* cause endothrix infection, *T. tonsurans* is the more frequent answer in the context of standard medical examinations unless specific geographical or clinical clues are provided. * **Microsporum (D):** Most *Microsporum* species (e.g., *M. audouinii*, *M. canis*) cause **Ectothrix** infections, where spores form a sheath around the outside of the hair shaft. These typically fluoresce under **Wood’s lamp**, whereas endothrix infections (like *T. tonsurans*) do not. **High-Yield Clinical Pearls for NEET-PG:** * **Endothrix (Inside):** *T. tonsurans*, *T. violaceum*. (Mnemonic: **TV** is watched **Inside**). * **Ectothrix (Outside):** *Microsporum* species, *T. mentagrophytes*. * **Wood’s Lamp:** Ectothrix (Microsporum) shows **Bright Green** fluorescence; Endothrix (T. tonsurans) is **Negative**. * **Favus:** Caused by *T. schoenleinii*, characterized by **scutula** (crusts) and permanent alopecia.

Question 34: Cerebral infarction is caused by which of the following fungi?

A. Toxoplasma
B. Cryptococcus
C. Aspergillus
D. Mucor (Correct Answer)

Explanation: **Explanation:** The correct answer is **Mucor**. The underlying medical concept is **angioinvasion**. **1. Why Mucor is correct:** Fungi belonging to the order Mucorales (Mucor, Rhizopus, Lichtheimia) are characterized by their aggressive ability to invade blood vessel walls (angioinvasion). In patients with predisposing factors like uncontrolled Diabetes Mellitus (especially DKA) or immunosuppression, these fungi cause **Rhinocerebral Mucormycosis**. The hyphae penetrate the endothelial lining, leading to thrombosis, vessel occlusion, and subsequent **hemorrhagic cerebral infarction** and necrosis. **2. Why other options are incorrect:** * **Toxoplasma:** While it causes ring-enhancing lesions in the brain (especially in HIV patients), it is a protozoan, not a fungus, and typically causes encephalitis rather than primary infarction. * **Cryptococcus:** This fungus typically presents as chronic meningitis or meningoencephalitis. It spreads via the Virchow-Robin spaces (causing "soap bubble" lesions) but is not primarily angioinvasive. * **Aspergillus:** While *Aspergillus* is also angioinvasive and can cause infarction, **Mucor** is the classic association for rapid, fulminant cerebral infarction in the context of the "Rhinocerebral" clinical presentation often tested in NEET-PG. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Mucor has broad, **aseptate** hyphae with **wide-angled (90°)** branching. (Contrast with Aspergillus: narrow, septate, 45° branching). * **Clinical Sign:** Look for a **black eschar** on the palate or nasal turbinates. * **Treatment:** Surgical debridement + Liposomal **Amphotericin B**. Isavuconazole is an alternative. * **Predisposition:** Ketone reductase enzyme in *Rhizopus* allows it to thrive in acidic environments (DKA).

Question 35: Blastomycosis is characterized by which of the following features, except?

A. Yeast-like fungus
B. Commonly involves lung and skin
C. Dimorphic fungus
D. Common in South America (Correct Answer)

Explanation: **Explanation:** **Blastomycosis** is a systemic fungal infection caused by *Blastomyces dermatitidis*. The correct answer is **Option D** because Blastomycosis is primarily endemic to the **Ohio and Mississippi River Valleys** and the Great Lakes region of North America. It is **not** common in South America; that geographical niche is characteristic of *Paracoccidioides brasiliensis* (South American Blastomycosis). **Analysis of Options:** * **Option A & C (Yeast-like & Dimorphic):** *Blastomyces* is a classic **dimorphic fungus**. It exists as a mold in the environment (soil/decaying wood) and transforms into a **yeast** form at 37°C within the human body. * **Option B (Lung and Skin involvement):** The primary route of infection is inhalation of spores, making the **lungs** the most common site of involvement (pneumonia). **Skin** is the most common site of extrapulmonary dissemination, presenting as verrucous or ulcerative lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopic Appearance:** Characterized by **Broad-Based Budding** yeast with thick, doubly refractile walls ("B" for Blastomyces, "B" for Broad-Based Budding). * **Size:** The yeast cells are roughly the same size as a red blood cell (8–15 µm). * **Clinical Presentation:** Often mimics tuberculosis or lung cancer on imaging. * **Treatment:** Itraconazole for mild-to-moderate disease; Amphotericin B for severe or CNS involvement. * **Geographic Mnemonic:** * *Blastomyces:* North America (Great Lakes). * *Coccidioides:* Southwest USA (San Joaquin Valley). * *Histoplasma:* Ohio/Mississippi River Valley (Bird/Bat droppings). * *Paracoccidioides:* South/Central America (Pilot’s Wheel appearance).

Question 36: A 53-year-old woman with end-stage renal disease who received a kidney transplant was maintained on an immunosuppressive regimen. Three months later, she developed a fever (38.3°C) and acute renal failure. Renal transplant biopsy was performed, and Periodic acid-Schiff staining showed yeast cells and hyphae. What is the most likely causative organism for this patient's infection?

A. Aspergillus fumigatus
B. Candida albicans (Correct Answer)
C. Candida glabrata
D. Cryptococcus neoformans

Explanation: ### Explanation **Correct Answer: B. Candida albicans** The clinical presentation of a post-transplant patient on immunosuppressants developing fever and renal failure, combined with the histopathological finding of **both yeast cells and hyphae**, is classic for *Candida albicans*. * **Underlying Concept:** *Candida albicans* is a dimorphic fungus (though often referred to as polymorphic) that exists as oval budding yeast cells and produces **pseudohyphae** and **true hyphae** in tissue. In immunocompromised states (like post-transplant), it can cause disseminated candidiasis, often involving the kidneys. The PAS (Periodic acid-Schiff) stain is excellent for highlighting these fungal elements in tissue sections. **Analysis of Incorrect Options:** * **A. Aspergillus fumigatus:** This is a filamentous fungus. It presents only as **septate hyphae** with acute-angle (45°) branching; it **does not** form yeast cells. * **C. Candida glabrata:** Unlike *C. albicans*, *C. glabrata* exists **only as yeast cells** and does not form hyphae or pseudohyphae. It is also smaller in size. * **D. Cryptococcus neoformans:** This is an encapsulated yeast. In tissue, it appears as **round-to-oval budding yeast** with a prominent polysaccharide capsule (visible on India ink or Mucicarmine stain). It **does not** form hyphae. **NEET-PG High-Yield Pearls:** * **Germ Tube Test:** Positive for *C. albicans* (Reynolds-Braude phenomenon). * **Chlamydospores:** *C. albicans* produces thick-walled terminal chlamydospores on Cornmeal agar. * **Morphology Rule:** If you see "Yeast + Hyphae/Pseudohyphae" in a biopsy, think *Candida albicans*. If you see "Only Hyphae," think *Aspergillus*. If you see "Only Yeast," think *Cryptococcus* or *Histoplasma*.

Question 37: Which of the following is a non-culturable fungus?

A. Rhinosporidium (Correct Answer)
B. Candida
C. Sporothrix
D. Penicillium

Explanation: **Explanation:** The correct answer is **Rhinosporidium seeberi**. Despite its name and fungal-like presentation, *Rhinosporidium seeberi* is a unique organism currently classified under **Mesomycetozoea** (a group of fish parasites). It is famously known in medical microbiology as a **non-culturable** organism because it has never been successfully grown on artificial laboratory media (like SDA) or in cell cultures. Diagnosis relies entirely on histopathology, showing characteristic thick-walled **sporangia** filled with thousands of **sporangiospores**. **Analysis of Incorrect Options:** * **Candida:** A common yeast that grows rapidly (24–48 hours) on Sabouraud Dextrose Agar (SDA) as creamy white colonies. It is easily cultured from clinical samples. * **Sporothrix:** A dimorphic fungus that causes "Rose gardener’s disease." It can be cultured at 25°C (mold form with "flower-like" sporulation) and 37°C (yeast form). * **Penicillium:** A common saprophytic filamentous fungus that grows readily on standard mycological media, producing characteristic brush-like conidiophores. **High-Yield Clinical Pearls for NEET-PG:** * **Disease:** Rhinosporidiosis typically presents as friable, leafy, **strawberry-like polypoid masses** in the nose or nasopharynx. * **Transmission:** Associated with bathing in stagnant freshwater (ponds/lakes); common in South India (Tamil Nadu, Kerala) and Sri Lanka. * **Microscopy:** Look for large sporangia (up to 350 µm) visible even under low power, often stained with H&E, GMS, or PAS. * **Treatment:** Surgical excision with cauterization of the base is the mainstay, as medical therapy (Dapsone) has limited efficacy.

Question 38: At what angle do Aspergillus hyphae typically branch?

A. 45 degrees (Correct Answer)
B. 60-90 degrees
C. 90-120 degrees
D. None of the above

Explanation: **Explanation:** The morphological identification of fungi in tissue sections is a high-yield topic for NEET-PG. The correct answer is **45 degrees** because *Aspergillus* species are characterized by **septate hyphae** that exhibit **dichotomous branching at acute angles** (typically 45°). * **Why Option A is correct:** The term "dichotomous" means the hyphae split into two equal branches. In *Aspergillus*, this branching occurs consistently at an acute angle (45°), resembling a "V" shape. This is a hallmark histological feature used to identify the fungus in specimens like lung biopsies or "fungus balls" (Aspergillomas). * **Why Options B and C are incorrect:** These options describe wide or right-angled branching. **90-degree (right-angle) branching** is the characteristic feature of **Mucormycosis** (caused by *Rhizopus*, *Mucor*, etc.). Unlike *Aspergillus*, Mucorales have broad, **non-septate (coenocytic)** hyphae with irregular widths. **High-Yield Clinical Pearls for NEET-PG:** 1. **Morphology Mnemonic:** **A**spergillus = **A**cute angle (45°) + **A**septate is false (it is Septate). 2. **Culture:** *Aspergillus* grows on Sabouraud Dextrose Agar (SDA), producing velvety/powdery colonies. *A. fumigatus* is the most common pathogenic species. 3. **Staining:** Silver stains (GMS) and PAS are excellent for visualizing the septate hyphae. 4. **Clinical Presentation:** Look for "Monod’s Sign" (air crescent sign) on a chest X-ray, indicating an Aspergilloma within a pre-existing cavity.

Question 39: "Tuberculate spores" are characteristic features of which of the following fungi?

A. Candida
B. Histoplasma (Correct Answer)
C. Coccidioides
D. Cryptococcus

Explanation: **Explanation:** The correct answer is **Histoplasma capsulatum**. **Why Histoplasma is correct:** *Histoplasma capsulatum* is a dimorphic fungus. In its mold form (at 25°C), it produces two types of spores: microconidia and **macroconidia**. The macroconidia are large, thick-walled, and spherical with finger-like projections on the surface, giving them a "bumpy" or **tuberculate** appearance. These tuberculate macroconidia are the definitive diagnostic morphological feature used for identification in the laboratory. **Why the other options are incorrect:** * **Candida:** Characterized by budding yeast cells, pseudohyphae, and **chlamydospores** (thick-walled resting spores seen specifically in *C. albicans* on cornmeal agar). * **Coccidioides:** Characterized by **spherules** containing endospores in tissue samples and **arthroconidia** (barrel-shaped spores) in culture. * **Cryptococcus:** A monomorphic yeast identified by its thick **polysaccharide capsule** (visualized with India Ink) and narrow-based budding. It does not produce tuberculate spores. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Associated with **soil enriched with bird or bat guano** (caving/spelunking). * **Intracellular Pathogen:** In the yeast phase (37°C), it is found inside **macrophages** (seen as small oval yeasts with a "halo" that mimics a capsule, though it is actually a capsule-less fungus). * **Clinical Presentation:** Can mimic Tuberculosis (calcified granulomas in lungs/spleen). * **Diagnosis:** Best diagnosed via **Urinary Antigen test** or fungal culture showing tuberculate macroconidia.

Question 40: Germ tubes are formed mainly by which organism?

A. Candida albicans (Correct Answer)
B. Candida stellatoidea
C. Candida tropicalis
D. Candida pseudotropicalis

Explanation: **Explanation:** The **Germ Tube Test (Reynold-Braude Phenomenon)** is a rapid diagnostic test used to differentiate *Candida albicans* from other species. When *C. albicans* is incubated in human or rabbit serum at 37°C for 2–3 hours, it produces initial hyphae called **germ tubes**. These are true hyphae that lack constriction at their point of origin from the yeast cell, a key morphological feature. **Analysis of Options:** * **A. Candida albicans (Correct):** It is the primary medically important yeast that is germ tube positive. Along with *Candida dubliniensis*, it is categorized as "Albicans-group" based on this test. * **B. Candida stellatoidea:** While some older classifications consider it a variant of *C. albicans* that can produce germ tubes, it is rarely encountered clinically and is not the "main" organism associated with this test in standard medical curriculum. * **C. Candida tropicalis:** This species is typically germ tube negative. However, it may occasionally produce "pseudo-germ tubes" (long pseudohyphae), but these always show **constriction** at the point of origin, unlike true germ tubes. * **D. Candida pseudotropicalis (*C. kefyr*):** It is germ tube negative and characteristically shows a "logs-in-stream" appearance on cornmeal agar. **High-Yield Clinical Pearls for NEET-PG:** * **Culture Media:** *C. albicans* produces thick-walled **Chlamydospores** on Cornmeal Agar (Dalmau Plate technique). * **Chromogenic Agar (CHROMagar):** *C. albicans* produces light green colonies, while *C. tropicalis* produces blue/metallic blue colonies. * **Drug of Choice:** Fluconazole is the standard treatment for most *Candida* infections, but *C. krusei* is inherently resistant. * **Morphology:** *Candida* is a polymorphic fungus (exists as yeast, pseudohyphae, and true hyphae).

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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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