Mycology — MCQs
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"Asteroid bodies" and "cigar shaped globi" may be produced by which of the following?
Cigar bodies are seen in which condition?
Candida is most often implicated in causation of which condition?
Which of the following methods is used for the rapid identification of Candida?
Which of the following statements about Pneumocystis pneumonia is true?
All are true about Madura mycetoma except?
Which of the following is true about Histoplasma capsulatum?
Pneumocystis carinii is classified as a fungus because?
An AIDS patient presents with broad budding yeast. What is the likely causative organism?
Aseptate hyphae are seen in which group of fungi?
Mycology Indian Medical PG Practice Questions and MCQs
Question 21: "Asteroid bodies" and "cigar shaped globi" may be produced by which of the following?
- A. Sporothrix
- B. Sporotrichosis (Correct Answer)
- C. Phialophora
- D. Aspergillus
Explanation: **Explanation:** The correct answer is **Sporotrichosis**, a subcutaneous mycosis caused by the dimorphic fungus *Sporothrix schenckii*. **Why it is correct:** * **Asteroid Bodies:** These are found in tissue sections and represent a **Splendore-Hoeppli phenomenon**. They consist of a central yeast cell surrounded by radiating eosinophilic material (antigen-antibody complexes). * **Cigar-shaped Globi:** In its yeast phase (at 37°C or in tissue), *Sporothrix* typically appears as pleomorphic, elongated, or fusiform budding cells, often described as "cigar-shaped." **Analysis of Incorrect Options:** * **A. Sporothrix:** While *Sporothrix* is the causative agent, the question asks what "produces" these features. In medical entrance exams, the disease entity (**Sporotrichosis**) is often preferred over the genus name when describing pathological findings seen *in vivo*. * **C. Phialophora:** This is a causative agent of **Chromoblastomycosis**, characterized by "Medlar bodies" (Copper penny bodies/sclerotic bodies), not asteroid bodies. * **D. Aspergillus:** This fungus is characterized by septate hyphae with acute-angle (45°) branching and fruiting bodies, not cigar-shaped yeasts. **Clinical Pearls for NEET-PG:** * **Occupation:** Classically associated with gardeners and florists (traumatic inoculation via thorns), hence called **"Rose Gardener’s Disease."** * **Clinical Presentation:** Presents as a linear chain of nodules along the lymphatics (**Lymphocutaneous sporotrichosis**). * **Culture:** At 25°C, it shows a "Flower-like" or "Daisy-petal" arrangement of conidia. * **Treatment:** Drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.
Question 22: Cigar bodies are seen in which condition?
- A. Sporotrichosis (Correct Answer)
- B. Chromoblastomycosis
- C. Mycetoma
- D. Basidiomycosis
Explanation: **Explanation:** **Sporotrichosis** is a subcutaneous fungal infection caused by the dimorphic fungus *Sporothrix schenckii*. The correct answer is **A** because "Cigar bodies" are the characteristic tissue form of this fungus. * **Why it is correct:** In tissue biopsies (at 37°C), *Sporothrix schenckii* exists as pleomorphic, elongated, fusiform yeast cells measuring 1–3 µm by 3–10 µm. Their elongated shape resembles a cigar, hence the term **"Cigar bodies."** These are often difficult to visualize on routine H&E stains and are better seen with PAS or GMS stains. **Why other options are incorrect:** * **Chromoblastomycosis:** Characterized by **Medlar bodies** (Sclerotic bodies/Copper-penny bodies), which are thick-walled, dark brown, multiseptate fungal cells. * **Mycetoma:** Characterized by the presence of **grains** or granules (sulfur granules in actinomycetoma or fungal hyphae in eumycetoma) draining from sinuses. * **Basidiomycosis:** Typically presents as subcutaneous zygomycosis (e.g., *Conidiobolus*), characterized by thin-walled, sparsely septate hyphae often surrounded by an eosinophilic halo (**Splendore-Hoeppli phenomenon**). **High-Yield Clinical Pearls for NEET-PG:** * **Occupational Hazard:** Known as **"Rose Gardener’s Disease"** due to traumatic inoculation via thorns. * **Clinical Presentation:** Presents as a linear chain of nodules along the lymphatic drainage (**Sporotrichoid spread**). * **Asteroid Bodies:** In tissue, yeast cells may be surrounded by eosinophilic radiating processes (Splendore-Hoeppli phenomenon), termed Asteroid bodies. * **Culture:** At 25°C, it shows a "Flower-like" or **"Daisy petal"** arrangement of conidia. * **Treatment:** Drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.
Question 23: Candida is most often implicated in causation of which condition?
- A. Conjunctivitis
- B. Tinea capitis
- C. Dese rheumatism
- D. Thrush (Correct Answer)
Explanation: **Explanation:** **Candida albicans** is a polymorphic opportunistic fungus that exists as part of the normal flora in the oral cavity, gastrointestinal tract, and vagina. **Why Thrush is the Correct Answer:** **Oral Thrush (Pseudomembranous Candidiasis)** is the most common clinical manifestation of *Candida* infection. It is characterized by creamy white, curd-like patches on the tongue and buccal mucosa that can be easily scraped off, leaving behind an erythematous (red) base. It occurs frequently in neonates, denture wearers, and immunocompromised individuals (e.g., HIV/AIDS, patients on broad-spectrum antibiotics or inhaled corticosteroids). **Analysis of Incorrect Options:** * **A. Conjunctivitis:** Most commonly caused by viruses (Adenovirus) or bacteria (*Staphylococcus aureus*, *Haemophilus influenzae*). While *Candida* can cause endophthalmitis (usually via hematogenous spread), it is a rare cause of primary conjunctivitis. * **B. Tinea capitis:** This is a fungal infection of the scalp caused by **Dermatophytes** (genera *Trichophyton* and *Microsporum*), not *Candida*. Dermatophytes require keratin for growth, whereas *Candida* prefers moist mucosal surfaces. * **C. Dese rheumatism:** This appears to be a distractor or a misspelling of "Desert Rheumatism," which is a clinical manifestation of **Coccidioidomycosis** (caused by *Coccidioides immitis*), characterized by fever, joint pain, and erythema nodosum. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Candida* shows Gram-positive budding yeast cells and **pseudohyphae**. * **Germ Tube Test (Reynolds-Braude Phenomenon):** The definitive rapid diagnostic test for *C. albicans*. * **Culture:** Produces "creamy white" colonies on Sabouraud Dextrose Agar (SDA). * **Chlamydospores:** Produced on Cornmeal agar at 25°C. * **Risk Factors:** Diabetes mellitus, prolonged antibiotic use, and T-cell deficiency are major predispositions.
Question 24: Which of the following methods is used for the rapid identification of Candida?
- A. Culture in solid media
- B. Germ tube method (Correct Answer)
- C. Growth in an animal model
- D. Culture in liquid media
Explanation: ### Explanation **Correct Option: B. Germ tube method** The **Germ tube test** (also known as the Reynolds-Braude phenomenon) is the gold standard for the rapid presumptive identification of *Candida albicans* and *Candida dubliniensis*. * **Mechanism:** When *C. albicans* cells are incubated in human or rabbit serum at 37°C for 2–3 hours, they produce short, lateral hyphal extensions called **germ tubes**. * **Key Feature:** A true germ tube has **no constriction** at its point of origin from the parent yeast cell (unlike pseudohyphae). This test provides results within hours, making it significantly faster than traditional culture. **Analysis of Incorrect Options:** * **A & D (Culture in solid/liquid media):** While *Candida* grows readily on Sabouraud Dextrose Agar (SDA) or in liquid broth, these methods require 24–48 hours for visible growth. They are used for isolation but are not considered "rapid" identification methods compared to the germ tube test. * **C (Growth in an animal model):** Historically, the "Rabbit Pathogenicity Test" was used to confirm virulence, but it is expensive, time-consuming, and ethically restricted. It is never used for routine clinical identification. **High-Yield Clinical Pearls for NEET-PG:** * **Chlamydospore Formation:** *C. albicans* produces thick-walled terminal chlamydospores on **Cornmeal Agar** (Dalmau technique). * **CHROMagar:** A specialized differential medium where *Candida* species produce different colors (e.g., *C. albicans* is light green, *C. tropicalis* is blue/metallic blue). * **Drug Resistance:** *C. glabrata* and *C. krusei* are notorious for intrinsic or emerging resistance to Azoles. * **Morphology:** *Candida* is a "dimorphic" fungus in a unique sense—it exists as yeast at room temperature and forms hyphae/germ tubes at body temperature (37°C).
Question 25: Which of the following statements about Pneumocystis pneumonia is true?
- A. The causative organism is a protozoan.
- B. The drug of choice is Trimethoprim-Sulfamethoxazole (Cotrimoxazole). (Correct Answer)
- C. The most common radiological appearance is a bat wing distribution of infiltrates with pneumocysts in peripheral fields.
- D. Steroids have no role in the therapy of Pneumocystis pneumonia.
Explanation: **Explanation:** **Pneumocystis jirovecii** (formerly *P. carinii*) is a unique fungus that causes life-threatening pneumonia (PCP) in immunocompromised individuals, particularly those with HIV/AIDS (CD4 count <200 cells/μL). 1. **Why Option B is Correct:** **Trimethoprim-Sulfamethoxazole (TMP-SMX)** is the gold standard for both the treatment and prophylaxis of PCP. It acts by inhibiting the folic acid synthesis pathway of the organism. In cases of severe allergy, alternatives like Pentamidine or Atovaquone are used. 2. **Why Other Options are Incorrect:** * **Option A:** Historically classified as a protozoan due to its morphology and lack of ergosterol, DNA analysis has confirmed it is a **fungus**. However, unlike most fungi, it does not respond to standard antifungals like Amphotericin B. * **Option C:** The classic radiological finding is **bilateral, symmetrical, diffuse ground-glass opacities** extending from the perihilar region. While it can resemble a "bat wing" appearance, the infiltrates typically involve the entire lung; "pneumocysts in peripheral fields" is not a standard radiological description. * **Option D:** **Corticosteroids** are a critical adjunct therapy in moderate-to-severe cases (defined by $PaO_2 < 70$ mmHg or $A-a$ gradient $> 35$ mmHg) to reduce the inflammatory response triggered by dying organisms. **High-Yield Clinical Pearls for NEET-PG:** * **Stain of Choice:** **Gomori Methenamine Silver (GMS)** stain, which highlights "crushed ping-pong ball" shaped cysts. * **Diagnosis:** Bronchoalveolar lavage (BAL) is the most common diagnostic procedure. * **Serum Marker:** Elevated **(1,3)-beta-D-glucan** levels are often seen (non-specific but sensitive). * **Prophylaxis:** Indicated in HIV patients when CD4 count falls below **200 cells/μL**.
Question 26: All are true about Madura mycetoma except?
- A. Fungal infection
- B. Presented as a painful nodular lesion for many months (Correct Answer)
- C. Discharging sinuses
- D. Bone involvement seen
Explanation: ### Explanation: Madura Mycetoma **Madura mycetoma** (Maduramycosis) is a chronic, granulomatous, subcutaneous infection typically involving the foot. The hallmark of this condition is its **painless** progression, which is why Option B is the correct "except" answer. #### 1. Why Option B is the Correct Answer (The "Except") Mycetoma is characterized by a **painless**, slow-growing subcutaneous nodule. Despite significant swelling and bone destruction, the lesion remains remarkably non-tender unless there is a secondary bacterial infection. The chronicity (lasting months to years) is accurate, but the description of it being "painful" is clinically incorrect for an uncomplicated case. #### 2. Analysis of Other Options * **Option A (Fungal infection):** True. Mycetoma is classified into two types: **Eumycetoma** (caused by fungi like *Madurella mycetomatis*) and **Actinomycetoma** (caused by filamentous bacteria like *Nocardia* or *Actinomadura*). Madura mycetoma specifically refers to the fungal etiology. * **Option C (Discharging sinuses):** True. As the lesion progresses, it forms multiple interconnected tracks that erupt through the skin as sinuses, discharging serosanguinous fluid containing characteristic **grains**. * **Option D (Bone involvement):** True. If left untreated, the infection spreads from the subcutaneous tissue to the underlying fascia and bones, causing **osteomyelitis** and "punched-out" lytic lesions (seen on X-ray). #### 3. Clinical Pearls for NEET-PG * **The Triad:** Tumefaction (swelling), discharging sinuses, and presence of grains (sulfur granules). * **Dot-in-Circle Sign:** A pathognomonic MRI finding where small dark spots (grains) are seen within high-intensity inflammatory circles. * **Grains:** The color of the grain helps identify the agent (e.g., **Black grains** = *Madurella mycetomatis*; **Yellow/White grains** = *Actinomadura madurae*). * **Treatment:** Eumycetoma (fungal) requires long-term antifungals (Itraconazole) and often surgery; Actinomycetoma (bacterial) responds well to the **Welsh regimen** (Amikacin + Cotrimoxazole).
Question 27: Which of the following is true about Histoplasma capsulatum?
- A. It is a dimorphic fungus. (Correct Answer)
- B. It is the causative organism of moniliasis.
- C. It is the causative organism of valley fever.
- D. It is capsulated.
Explanation: ### Explanation **1. Why Option A is Correct:** *Histoplasma capsulatum* is a classic **systemic dimorphic fungus**. Dimorphism is the ability of a fungus to exist in two distinct morphological forms depending on environmental conditions (primarily temperature). * **At 25°C (Soil/Culture):** It grows as a **mold** with characteristic tuberculate macroconidia (thick-walled spores with finger-like projections). * **At 37°C (In host tissue):** It transforms into an **intracellular yeast**, typically found within macrophages. **2. Why the Other Options are Incorrect:** * **Option B:** **Moniliasis** is an older clinical term for **Candidiasis**, caused by *Candida albicans*, not *Histoplasma*. * **Option C:** **Valley Fever** (Desert Rheumatism) is caused by ***Coccidioides immitis***. *Histoplasma* causes "Darling’s Disease" or "Ohio Valley Disease." * **Option D:** Despite its name (*capsulatum*), **it is NOT capsulated**. The name was a historical misnomer; the "halo" seen around the yeast cells in tissue sections is actually an artifact caused by cytoplasm shrinkage away from the cell wall during staining. **3. High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Found in soil enriched with **bird or bat droppings** (guano); common among cave explorers (spelunkers). * **Pathogenesis:** It is an **obligate intracellular parasite** of the Reticuloendothelial system (Macrophages). * **Diagnosis:** * **Microscopy:** Small oval yeasts inside macrophages (Gomori Methenamine Silver/PAS stain). * **Culture:** Sabouraud Dextrose Agar (SDA) shows white-to-brown filamentous colonies. * **Clinical Presentation:** Often mimics Tuberculosis (calcified granulomas in lungs/spleen). In HIV patients, it causes disseminated disease.
Question 28: Pneumocystis carinii is classified as a fungus because?
- A. Its ribosomal RNA, mitochondrial protein gene sequence, and presence of thymidylate synthase.
- B. Its cell wall contains glucans.
- C. Antifungals are effective against P. carinii.
- D. All of the above. (Correct Answer)
Explanation: **Explanation:** *Pneumocystis jirovecii* (formerly *P. carinii*) was historically classified as a protozoan due to its morphology (trophozoites and cysts) and lack of response to traditional antifungals like Amphotericin B. However, modern molecular and biochemical evidence has firmly reclassified it as a **fungus**. **Why Option D is Correct:** * **Molecular Evidence (Option A):** Phylogenetic analysis of its **18S ribosomal RNA**, mitochondrial protein gene sequences, and the structure of its **thymidylate synthase** enzyme show a closer genetic affinity to fungi (specifically Ascomycetes) than to protozoa. * **Cell Wall Composition (Option B):** The cell wall of *Pneumocystis* contains **glucans** (specifically β-1,3-glucan), which is a hallmark of fungal cell walls. This is the target for Echinocandins, though they are only active against the cyst stage. * **Antifungal Sensitivity (Option C):** While it is resistant to many drugs, it is sensitive to certain antifungal-like actions. More importantly, its biochemical pathways align with fungal metabolism. Note: While Co-trimoxazole is the drug of choice, the biological classification is based on the organism's inherent fungal machinery. **Clinical Pearls for NEET-PG:** * **Taxonomy:** It is an atypical, unicellular fungus. * **Staining:** **Gomori Methenamine Silver (GMS)** stain is the gold standard for visualizing the characteristic "crushed ping-pong ball" appearance of cysts. * **Cell Membrane:** Unlike most fungi, *Pneumocystis* **lacks ergosterol** in its cell membrane (it contains cholesterol instead), which explains why Amphotericin B and Azoles are ineffective. * **Clinical Presentation:** It is the most common opportunistic infection in HIV/AIDS patients (CD4 count <200 cells/µL), typically presenting as interstitial plasma cell pneumonia. * **Drug of Choice:** Trimethoprim-Sulfamethoxazole (Co-trimoxazole).
Question 29: An AIDS patient presents with broad budding yeast. What is the likely causative organism?
- A. Histoplasmosis
- B. Blastomycosis (Correct Answer)
- C. Coccidioidomycosis
- D. Paracoccidioidomycosis
Explanation: **Explanation:** The correct answer is **Blastomycosis (*Blastomyces dermatitidis*)**. In medical mycology, the morphology of the yeast cell is a high-yield diagnostic feature. Blastomycosis is classically characterized by **large, thick-walled yeast cells with broad-based budding**. The daughter cell remains attached to the parent cell by a wide neck, often described as having a "double-contoured" appearance. While it is more common in immunocompetent individuals in endemic areas (Ohio and Mississippi River valleys), it can present as a severe, disseminated infection in AIDS patients. **Analysis of Incorrect Options:** * **Histoplasmosis:** Characterized by **small, oval yeast cells** (2–4 µm) typically found **intracellularly** within macrophages. It does not show broad-based budding. * **Coccidioidomycosis:** This fungus does not exist as a yeast in tissue; instead, it forms **large thick-walled spherules** filled with endospores. * **Paracoccidioidomycosis:** Characterized by large yeast cells with **multiple buds** attached by narrow necks, giving it a "pilot’s wheel" or "Mickey Mouse" appearance. **NEET-PG High-Yield Pearls:** * **Blastomycosis:** "Broad-Based Budding" (BBB) = **B**lastomycosis. * **Histoplasmosis:** "Holes" in macrophages (intracellular). * **Cryptococcus:** Narrow-based budding with a prominent polysaccharide capsule (India Ink positive). * **Paracoccidioidomycosis:** "Pilot’s wheel" appearance. * **Coccidioidomycosis:** "Spherules" in tissue; highly infectious arthroconidia in culture.
Question 30: Aseptate hyphae are seen in which group of fungi?
- A. Phycomycetes (Correct Answer)
- B. Ascomycetes
- C. Basidiomycetes
- D. Deuteromycetes
Explanation: ### Explanation **1. Why Phycomycetes is Correct:** Fungi are classified based on the presence or absence of cross-walls (septa) in their hyphae. **Phycomycetes** (which includes the medically important orders **Mucorales** and **Entomophthorales**) are characterized by **aseptate** (coenocytic) or sparsely septate hyphae. In these fungi, the cytoplasm is continuous, containing multiple nuclei. Under the microscope, they appear as broad, ribbon-like structures with irregular branching, typically at right angles (90°). **2. Why the Other Options are Incorrect:** * **Ascomycetes (e.g., *Aspergillus*, *Penicillium*):** These possess **septate** hyphae with regular cross-walls. They typically show narrow hyphae with acute-angle (45°) branching. * **Basidiomycetes (e.g., *Cryptococcus*):** These also have **septate** hyphae. They are characterized by the production of sexual spores on a club-shaped basidium. * **Deuteromycetes (Fungi Imperfecti):** This is a heterogeneous group where the sexual stage is unknown. Most medically important fungi (like *Candida* or Dermatophytes) were historically placed here; they possess **septate** hyphae. **3. Clinical Pearls for NEET-PG:** * **Mucormycosis:** Caused by members of Phycomycetes (e.g., *Rhizopus*, *Mucor*). It is a medical emergency, especially in uncontrolled diabetics (Ketoacidosis) or post-COVID patients. * **Histopathology Key:** Look for "Broad, ribbon-like, aseptate hyphae with right-angle branching" to diagnose Mucormycosis. * **Contrast:** *Aspergillus* shows "Septate hyphae with dichotomous acute-angle branching." * **Zygomycetes:** This term is often used interchangeably with Phycomycetes in older texts; both refer to the aseptate group.
Practice by Chapter
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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