Mycology — MCQs
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Which of the following fungal infections is a leading cause of corneal ulcer?
Which of the following organisms is NOT typically cultured in a laboratory setting?
Blastomycosis may involve any of the following organs except?
Cerebral infarction is caused by which of the following agents?
A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?
A 25-year-old renal transplant recipient died of meningitis. On autopsy, gelatinous exudates with cystic masses were seen, and a round, encapsulated organism was isolated. Which is the best stain for diagnosis?
Which fungal infection is commonly found in patients with uncontrolled diabetes?
Candidal hyphae can be stained using which of the following stains?
Which of the following statements regarding aspergillosis is not true?
Eucalyptus camaldulensis is associated with the transmission of which of the following fungi?
Mycology Indian Medical PG Practice Questions and MCQs
Question 231: Which of the following fungal infections is a leading cause of corneal ulcer?
- A. Trichophyton
- B. Aspergillus (Correct Answer)
- C. Mucor
- D. Sporothrix
Explanation: **Explanation:** **1. Why Aspergillus is the correct answer:** Mycotic keratitis (fungal corneal ulcer) is a significant cause of ocular morbidity, especially in tropical regions. **Aspergillus species** (particularly *A. flavus* and *A. fumigatus*) are the most common cause of fungal corneal ulcers worldwide, followed closely by *Fusarium*. These infections typically occur following **vegetative trauma** (e.g., injury with a branch, leaf, or agricultural tool), which introduces the conidia into the corneal stroma. Clinically, these ulcers often present with "feathery" borders, satellite lesions, and a dry, gray-white appearance. **2. Why the other options are incorrect:** * **Trichophyton:** This is a dermatophyte responsible for superficial infections of the skin, hair, and nails (Tinea). It does not typically involve the cornea. * **Mucor:** While *Mucor* species cause devastating Rhinocerebral Mucormycosis (especially in uncontrolled diabetics), they primarily cause orbital cellulitis and tissue necrosis through angioinvasion rather than isolated corneal ulcers. * **Sporothrix:** *Sporothrix schenckii* causes "Rose gardener’s disease" (lymphocutaneous sporotrichosis). While it can rarely cause ocular adnexal infection, it is not a leading cause of keratitis. **3. NEET-PG High-Yield Pearls:** * **Most common cause overall:** *Aspergillus* (filamentous fungi). * **Most common cause in contact lens users:** *Acanthamoeba* or *Pseudomonas*. * **Classic Clinical Sign:** Feathery margins and **satellite lesions** (small infiltrates away from the main ulcer). * **Diagnosis:** Potassium Hydroxide (KOH) mount of corneal scrapings is the rapid test of choice; Sabouraud Dextrose Agar (SDA) is used for culture. * **Drug of Choice:** Topical **Natamycin** (5%) is the gold standard for filamentous fungal keratitis.
Question 232: Which of the following organisms is NOT typically cultured in a laboratory setting?
- A. Sporothrix schenckii
- B. Rhinosporidium seeberi (Correct Answer)
- C. Candida albicans
- D. Aspergillus fumigatus
Explanation: **Explanation:** The correct answer is **Rhinosporidium seeberi**. **1. Why Rhinosporidium seeberi is the correct answer:** *Rhinosporidium seeberi* is a unique organism (historically classified as a fungus but now considered a protist belonging to the Mesomycetozoea group) that causes **Rhinosporidiosis**. The defining characteristic of this organism is that it **cannot be cultured on artificial laboratory media** (like SDA) or in cell lines. Diagnosis relies exclusively on clinical presentation and histopathology, where large, thick-walled **sporangia** containing thousands of **endospores** are visualized. **2. Why the other options are incorrect:** * **Sporothrix schenckii (A):** This is a dimorphic fungus that can be easily cultured. At 25°C, it grows as a mold (flower-like sporulation), and at 37°C, it grows as cigar-shaped yeast cells. * **Candida albicans (C):** This is the most common fungal isolate in clinical labs. It grows rapidly on Sabouraud Dextrose Agar (SDA) as creamy white colonies and produces germ tubes in serum. * **Aspergillus fumigatus (D):** This is a ubiquitous filamentous fungus that grows well on standard media, producing characteristic smoky-green velvety colonies with distinct conidiophores. **3. High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Rhinosporidiosis typically presents as leafy, friable, strawberry-like **polypoidal masses** in the nose or nasopharynx. * **Epidemiology:** Highly prevalent in South India (especially Tamil Nadu and Kerala) and Sri Lanka; often associated with bathing in stagnant water. * **Histopathology:** Look for the "Sporangium" (up to 350 µm)—much larger than the spherules of *Coccidioides*. * **Treatment:** Surgical excision with electrocautery of the base is the treatment of choice; medical therapy (Dapsone) has limited efficacy.
Question 233: Blastomycosis may involve any of the following organs except?
- A. Skin
- B. Lungs
- C. Lymphatics
- D. Intestinal tract (Correct Answer)
Explanation: **Explanation:** **Blastomycosis**, caused by the dimorphic fungus *Blastomyces dermatitidis*, is primarily a systemic pyogranulomatous infection. The correct answer is **Intestinal tract** because Blastomycosis is known for its predilection for the respiratory system and subsequent hematogenous spread to specific extrapulmonary sites, but it **rarely, if ever, involves the gastrointestinal tract.** 1. **Why Intestinal tract is correct:** Unlike *Histoplasmosis* (which frequently involves the reticuloendothelial system and can cause GI ulcerations), Blastomycosis does not typically affect the intestines. It is an "except" question, and the GI tract is not a recognized clinical feature of the disease. 2. **Why other options are incorrect:** * **Lungs (B):** The primary route of infection is inhalation of conidia. Pulmonary involvement is the most common presentation, ranging from asymptomatic infection to acute pneumonia or ARDS. * **Skin (A):** This is the most common **extrapulmonary** site (approx. 40-80% of cases). It presents as verrucous lesions with microabscesses or ulcerative lesions. * **Lymphatics (C):** While less common than skin or bone involvement, lymphadenopathy can occur as part of the systemic spread or secondary to pulmonary infection. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** In tissue (yeast form), it shows characteristic **Broad-Based Budding** with a thick, doubly refractile cell wall ("B" for Blastomyces, "B" for Broad-Based). * **Geography:** Endemic to the Ohio and Mississippi River valleys (similar to Histoplasma). * **Common Sites of Spread:** Remember the mnemonic **"LBS"** — **L**ungs, **B**one (osteomyelitis), and **S**kin. It also frequently involves the **Prostate** in males. * **Diagnosis:** KOH mount of sputum or skin scrapings; Culture on Sabouraud Dextrose Agar (SDA).
Question 234: Cerebral infarction is caused by which of the following agents?
- A. Toxoplasma (Correct Answer)
- B. Cryptococcus
- C. Aspergillus
- D. Mucor
Explanation: **Explanation:** The correct answer is **Toxoplasma gondii**. **1. Why Toxoplasma is correct:** *Toxoplasma gondii* is a protozoan parasite that commonly causes CNS infections in immunocompromised individuals (especially HIV/AIDS patients). The underlying mechanism for cerebral infarction in Toxoplasmosis is **necrotizing encephalitis** and **vasculitis**. The parasite can directly infect vascular endothelial cells, leading to inflammation, thrombosis, and subsequent ischemic infarction of the surrounding brain parenchyma. On imaging, this typically presents as multiple ring-enhancing lesions with associated edema. **2. Why the other options are incorrect:** * **Cryptococcus:** Primarily causes chronic meningitis or meningoencephalitis. While it can form "soap-bubble" lesions (gelatinous pseudocysts) in the basal ganglia, it rarely causes true cerebral infarction. * **Aspergillus & Mucor:** These are **angioinvasive fungi**. While they are notorious for invading blood vessel walls, they typically cause **hemorrhagic infarction** or mycotic aneurysms rather than the classic ischemic cerebral infarction associated with the vasculitis seen in Toxoplasmosis in this specific clinical context. **3. High-Yield Clinical Pearls for NEET-PG:** * **Toxoplasmosis:** Most common cause of CNS mass lesions in AIDS. Treatment: Sulfadiazine + Pyrimethamine. * **Imaging:** "Target sign" or "Eccentric target sign" on MRI is highly suggestive of Toxoplasmosis. * **Differential:** In an HIV patient with ring-enhancing lesions, if the patient does not respond to anti-toxoplasma therapy, the next most likely diagnosis is **Primary CNS Lymphoma** (associated with EBV). * **Mucormycosis:** Look for keywords like "diabetic ketoacidosis," "black eschar," and "broad non-septate hyphae."
Question 235: A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?
- A. AIDS (Correct Answer)
- B. Congestive heart failure
- C. Pulmonary embolus
- D. Rheumatoid arthritis
Explanation: ### Explanation The clinical presentation and microscopic findings point directly to **Pneumocystis pneumonia (PCP)**, caused by the fungus ***Pneumocystis jirovecii***. **1. Why the correct answer is right:** * **Clinical Presentation:** The triad of fever, dyspnea, and **bilateral interstitial (ground-glass) infiltrates** on X-ray is classic for PCP. * **Microscopy:** *P. jirovecii* cannot be cultured. Diagnosis relies on staining (Gomori Methenamine Silver - GMS). The description of **"hat-shaped,"** "cup-shaped," or "crushed ping-pong ball" cysts within the alveoli is pathognomonic for this organism. * **Predisposing Condition:** *P. jirovecii* is an opportunistic pathogen. It is the most common opportunistic infection in patients with **AIDS**, typically occurring when the **CD4+ T-cell count falls below 200 cells/mm³**. **2. Why the incorrect options are wrong:** * **Congestive heart failure (CHF):** While CHF causes bilateral infiltrates (pulmonary edema), it would not show silver-staining organisms in bronchial washings. * **Pulmonary embolus:** Usually presents with sudden pleuritic chest pain and a normal X-ray or focal wedge-shaped infarct (Hampton’s hump), not diffuse interstitial infiltrates or fungal cysts. * **Rheumatoid arthritis:** While RA can cause interstitial lung disease (ILD), it is a chronic process and would not demonstrate the specific "hat-shaped" organisms associated with acute infectious pneumonia. **3. NEET-PG High-Yield Pearls:** * **Stains of Choice:** **GMS stain** (best for cysts/hat-shape); **Giemsa/Wright stain** (shows trophic forms); **Direct Fluorescent Antibody (DFA)** is the most sensitive. * **Biochemical Marker:** Elevated **Serum Beta-D-Glucan** (non-specific but supportive). * **Drug of Choice:** **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Prophylaxis:** Indicated in HIV patients when CD4 count is **<200 cells/mm³**.
Question 236: A 25-year-old renal transplant recipient died of meningitis. On autopsy, gelatinous exudates with cystic masses were seen, and a round, encapsulated organism was isolated. Which is the best stain for diagnosis?
- A. Mucicarmine (Correct Answer)
- B. Alcian blue
- C. Giemsa
- D. Prussian blue
Explanation: ### **Explanation** The clinical presentation of meningitis in an immunocompromised patient (renal transplant recipient) with autopsy findings of **"gelatinous exudates"** and **"cystic masses"** (often called "soap-bubble" lesions) is classic for **Cryptococcosis**, caused by *Cryptococcus neoformans*. **1. Why Mucicarmine is correct:** *Cryptococcus neoformans* is unique among fungi because it possesses a thick **polysaccharide capsule** (composed of glucuronoxylomannan). **Mayer’s Mucicarmine** is the specific stain used to demonstrate this capsule, staining it a bright **rose-red/pink**. This is the gold standard for identifying the organism in tissue sections. **2. Why the other options are incorrect:** * **Alcian blue:** While it can stain the capsule of *Cryptococcus*, it is less specific than Mucicarmine in a clinical pathology context for this organism. It is more commonly used to identify acidic mucopolysaccharides in connective tissues. * **Giemsa:** This is a hematological stain used primarily for intracellular blood parasites (like *Plasmodium* or *Leishmania*) and certain bacteria (*Chlamydia*). It does not highlight the cryptococcal capsule. * **Prussian blue:** This stain is used to detect **iron** (hemosiderin) in tissues. It has no role in fungal identification. **3. NEET-PG High-Yield Pearls:** * **India Ink:** Used for CSF microscopy; shows a "negative staining" effect (halo) around the yeast. * **Nigrosin:** Another negative stain used for CSF. * **PAS (Periodic Acid-Schiff) & GMS (Gomori Methenamine Silver):** Stain the **cell wall** of the fungus, not the capsule. * **Fontana-Masson:** Stains the **melanin** in the cell wall of *Cryptococcus*. * **Urease Test:** *Cryptococcus* is characteristically urease positive.
Question 237: Which fungal infection is commonly found in patients with uncontrolled diabetes?
- A. Histoplasmosis
- B. Mucormycosis (Correct Answer)
- C. Cryptococcosis
- D. Rhinosporidiosis
Explanation: ### Explanation **Correct Answer: B. Mucormycosis** **Why it is correct:** Mucormycosis (caused by fungi of the order Mucorales, such as *Rhizopus* and *Mucor*) is an opportunistic infection strongly associated with **uncontrolled diabetes mellitus**, particularly during episodes of **Diabetic Ketoacidosis (DKA)**. * **The Mechanism:** These fungi possess an enzyme called **ketone reductase**, which allows them to thrive in acidic, high-glucose environments. Furthermore, DKA causes the release of iron from binding proteins (sequestration failure); the fungi utilize this free iron for rapid growth. The most common presentation in diabetics is **Rhinocerebral Mucormycosis**, characterized by angioinvasion, tissue necrosis (black eschar), and potential spread to the orbit and brain. **Why the other options are incorrect:** * **A. Histoplasmosis:** This is a systemic dimorphic fungal infection typically associated with bird or bat droppings (caves). While it can affect immunocompromised patients, it is not specifically linked to diabetes like Mucormycosis. * **C. Cryptococcosis:** Caused by *Cryptococcus neoformans*, this is the most common fungal meningitis in **HIV/AIDS patients** (CD4 count <100). Its primary association is cellular immunodeficiency rather than metabolic derangement. * **D. Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it typically presents as friable, strawberry-like nasal polyps in individuals who bathe in stagnant water. It is not associated with diabetes. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark:** Broad, **non-septate** hyphae with **right-angle (90°)** branching. * **Clinical Sign:** A **black eschar** on the palate or nasal turbinates is a classic board-exam clue. * **Treatment:** Surgical debridement and **Liposomal Amphotericin B**. (Note: Voriconazole is ineffective against Mucor). * **Risk Factors:** DKA, neutropenia, and iron overload (use of deferoxamine).
Question 238: Candidal hyphae can be stained using which of the following stains?
- A. Van Gieson's stain
- B. Periodic acid Schiff stain (Correct Answer)
- C. Masson Trichrome stain
- D. Toluidine blue stain
Explanation: **Explanation:** The correct answer is **Periodic acid Schiff (PAS) stain**. **1. Why PAS is the correct answer:** Fungal cell walls, including those of *Candida* species, are rich in polysaccharides like chitin, glucan, and mannan. The PAS stain works by oxidizing these carbohydrates (using periodic acid) to form aldehydes, which then react with the Schiff reagent to produce a brilliant **magenta or purplish-red color**. This makes PAS one of the most reliable and commonly used stains for visualizing fungal morphology (hyphae, pseudohyphae, and yeast cells) in tissue sections. **2. Why other options are incorrect:** * **Van Gieson’s stain:** Primarily used to differentiate between collagen (red) and smooth muscle (yellow) in connective tissue. * **Masson Trichrome stain:** Used to distinguish collagen fibers from muscle tissue (collagen stains blue/green, muscle stains red). * **Toluidine blue stain:** A metachromatic stain often used to highlight mast cells (granules stain purple) or to identify *Pneumocystis jirovecii* cysts, but it is not the standard for routine Candidal hyphae visualization. **3. High-Yield Clinical Pearls for NEET-PG:** * **Gomori Methenamine Silver (GMS):** This is the **gold standard** for fungal staining. Fungi appear black against a green background. * **Calcofluor White:** A fluorescent stain that binds to chitin; it is the most sensitive rapid method for identifying fungi in direct microscopy. * **Mucicarmine:** Specifically used to identify *Cryptococcus neoformans* (stains the polysaccharide capsule red). * **Germ Tube Test:** The specific diagnostic test for *Candida albicans* (Reynolds-Braude phenomenon).
Question 239: Which of the following statements regarding aspergillosis is not true?
- A. Aspergillus niger is the cause of fungal otitis externa.
- B. Aspergillosis is highly contagious. (Correct Answer)
- C. Aspergilloma is common in pre-existing tuberculosis or cystic lung disease.
- D. Aspergillus fumigatus is a cause of bronchial aspergillosis.
Explanation: ### Explanation **1. Why Option B is the Correct Answer (The False Statement):** Aspergillosis is **not contagious**. Unlike viral or bacterial respiratory infections, *Aspergillus* is not transmitted from person to person or from animals to humans. The infection is acquired exclusively through the **inhalation of fungal spores (conidia)** from the environment (soil, decaying vegetation, or dust). Since it is an opportunistic environmental pathogen rather than a communicable one, it does not spread between individuals. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** *Aspergillus niger* is a classic cause of **Otomycosis** (fungal otitis externa). It is clinically characterized by a "wet newspaper" appearance due to the presence of black spores and mycelia in the ear canal. * **Option C:** **Aspergilloma** (Fungus Ball) typically develops in pre-existing pulmonary cavities. The most common cause is healed **Tuberculosis**, but it can also occur in sarcoidosis or cystic lung disease. It appears as a mobile mass with a "Monod sign" (air crescent) on X-ray. * **Option D:** *Aspergillus fumigatus* is the most common species causing human disease, including **Allergic Bronchopulmonary Aspergillosis (ABPA)**, which is a hypersensitivity reaction in patients with asthma or cystic fibrosis. **3. NEET-PG High-Yield Clinical Pearls:** * **Morphology:** *Aspergillus* shows **septate hyphae** with **dichotomous branching** at acute angles (45°). * **Diagnosis:** The **Galactomannan antigen** test (ELISA) is a high-yield marker for Invasive Aspergillosis. * **Treatment:** **Voriconazole** is the drug of choice for invasive aspergillosis. * **Aflatoxins:** Produced by *Aspergillus flavus*, these are associated with **Hepatocellular Carcinoma**.
Question 240: Eucalyptus camaldulensis is associated with the transmission of which of the following fungi?
- A. Blastomyces dematitidis
- B. Histoplasma
- C. Cryptococcus (Correct Answer)
- D. Coccidioides immitis
Explanation: **Explanation:** The correct answer is **Cryptococcus**, specifically **Cryptococcus gattii**. **1. Why Cryptococcus is correct:** While *Cryptococcus neoformans* is famously associated with pigeon droppings, *Cryptococcus gattii* has a strong ecological niche in decaying hollows of certain trees. **Eucalyptus camaldulensis** (River Red Gum) and *Eucalyptus tereticornis* are the primary environmental reservoirs. Inhalation of basidiospores from these trees leads to infection. Unlike *C. neoformans*, which primarily affects immunocompromised patients, *C. gattii* is known to cause disease in **immunocompetent** individuals, often presenting with large pulmonary or CNS fungal granulomas (cryptococcomas). **2. Why the other options are incorrect:** * **Blastomyces dermatitidis:** Found in moist soil and decomposing organic matter (wood/leaves), primarily near waterways in the Mississippi and Ohio River valleys. It is not specifically linked to Eucalyptus. * **Histoplasma capsulatum:** Classically associated with soil enriched with **bird or bat guano** (caves, chicken coops). * **Coccidioides immitis:** Found in the alkaline, **semi-arid desert soil** of the Southwestern United States (San Joaquin Valley). **3. High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Cryptococcus is best visualized using **India Ink** (negative staining showing the polysaccharide capsule) or **Mucicarmine** (stains the capsule red). * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test via Latex Agglutination or LFA is the most sensitive diagnostic tool. * **C. gattii vs. C. neoformans:** *C. gattii* can be differentiated on **Canavanine-Glycine-Bromothymol Blue (CGB) agar**, where it turns the medium blue. * **Virulence Factor:** The thick polysaccharide capsule is the primary virulence factor, inhibiting phagocytosis.
Practice by Chapter
Classification of Fungi
Practice Questions
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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