Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 251: Which of the following is a true yeast?

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

Explanation: **Explanation:** In medical mycology, fungi are classified morphologically into four groups: yeasts, yeast-like fungi, molds, and dimorphic fungi. **1. Why Cryptococcus is the correct answer:** **Cryptococcus neoformans** is a **true yeast**. By definition, true yeasts are unicellular fungi that reproduce solely by budding and do not produce true hyphae or pseudohyphae under any conditions. A key diagnostic feature of *Cryptococcus* is its prominent polysaccharide capsule (visualized by India Ink), which is a major virulence factor. **2. Analysis of Incorrect Options:** * **Candida (Option A):** This is a **yeast-like fungus**. While it grows as budding yeast cells, it also forms **pseudohyphae** (elongated cells that remain attached) when invading tissues. *Candida albicans* can also form true hyphae (germ tubes). * **Aspergillus (Option D) & Rhizopus (Option C):** These are **molds (filamentous fungi)**. They grow as multicellular filaments called hyphae. *Aspergillus* is characterized by septate hyphae with acute-angle branching, while *Rhizopus* features broad, non-septate hyphae with right-angle branching. **Clinical Pearls for NEET-PG:** * **Cryptococcus:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 <100). Diagnosis is via India Ink (negative staining), Latex Agglutination (detects capsular antigen), and Bird Seed Agar (Niger Seed Agar). * **Candida:** The "Germ Tube Test" (Reynolds-Braude phenomenon) is the gold standard for identifying *C. albicans*. * **Morphology Rule:** If it forms pseudohyphae, it is "yeast-like"; if it only buds, it is a "true yeast."

Question 252: Fever with pulmonary disease leading to severe pneumonia if untreated, caused by which of the following dimorphic fungi?

A. Coccidioides immitis (Correct Answer)
B. Cryptococcus neoformans
C. Candida albicans
D. Aspergillus

Explanation: ### Explanation **Correct Option: A. Coccidioides immitis** *Coccidioides immitis* is a classic **dimorphic fungus** (existing as mold in soil and spherules in tissue). It is the causative agent of **Valley Fever**. While many infections are asymptomatic, it can present as a self-limiting respiratory illness or progress to **severe pneumonia** and disseminated disease in immunocompromised individuals. It is highly infectious; inhalation of a few arthroconidia can lead to disease. **Analysis of Incorrect Options:** * **B. Cryptococcus neoformans:** This is an **encapsulated yeast**, not a dimorphic fungus. While it can cause pulmonary nodules, it is most notorious for causing subacute or chronic meningitis in HIV/AIDS patients. * **C. Candida albicans:** This is a **yeast** (forming pseudohyphae and germ tubes), not dimorphic in the traditional sense (mold-to-yeast). It typically causes opportunistic infections like oral thrush or candidemia rather than primary severe pneumonia in immunocompetent hosts. * **D. Aspergillus:** This is a **monomorphic filamentous fungus** (mold only) characterized by septate hyphae with acute-angle branching. It causes Aspergilloma or Invasive Aspergillosis, but it does not exhibit dimorphism. **High-Yield Clinical Pearls for NEET-PG:** * **Dimorphic Fungi Mnemonic:** "**B**ody **H**as **C**apsule **S**haped **P**arasites" (**B**lastomyces, **H**istoplasma, **C**occidioides, **S**porothrix, **P**aracoccidioides). * **Morphology:** In the body (37°C), *Coccidioides* forms **Spherules filled with endospores** (unique because it doesn't form yeast cells). * **Geography:** Associated with the Southwestern US (California, Arizona) and alkaline desert soil. * **Diagnosis:** Identification of spherules in sputum or biopsy; culture is hazardous and must be handled in Biosafety Level 3 (BSL-3).

Question 253: Which of the following stains is used to study fungal morphology in tissue sections?

A. PAS (Correct Answer)
B. Von-Kossa
C. Alizarin Red
D. Masson's Trichrome

Explanation: **Explanation:** **Periodic Acid-Schiff (PAS)** is the correct answer because it is one of the most widely used stains for demonstrating fungi in tissue sections. The underlying mechanism involves the oxidation of polysaccharides (specifically **chitin and glucan**) present in the fungal cell wall by periodic acid to form aldehydes. These aldehydes then react with the Schiff reagent to produce a brilliant **magenta/pink** color, making the fungal morphology clearly visible against the tissue background. **Analysis of Incorrect Options:** * **Von-Kossa Stain:** This is used specifically to detect **calcium deposits** (carbonates and phosphates) in tissues. It stains calcium black. * **Alizarin Red:** This is another specialized stain for **calcium**, often used to identify calcium oxalate crystals or bone mineralization. * **Masson’s Trichrome:** This is a connective tissue stain used to differentiate between **collagen fibers** (blue/green) and muscle/cytoplasm (red). **High-Yield Clinical Pearls for NEET-PG:** * **Gomori Methenamine Silver (GMS):** This is considered the **best/gold standard** stain for fungi in histology. Fungi appear black against a green background. * **Mucicarmine:** Specifically used to identify ***Cryptococcus neoformans*** by staining its polysaccharide capsule bright red. * **India Ink:** Used for rapid identification of *Cryptococcus* in CSF (negative staining). * **Calcofluor White:** A fluorescent stain that binds to chitin; it is the most sensitive method for direct microscopic examination.

Question 254: In an asthmatic patient, the causative agent was found to be fungi with septate hyphae. What is the organism?

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

Explanation: ### Explanation The correct answer is **Aspergillus**. This question tests the clinical and morphological identification of medically important fungi. **1. Why Aspergillus is correct:** * **Morphology:** *Aspergillus* species are characterized by **narrow, septate hyphae** that exhibit **dichotomous branching** (branching at acute angles, approximately 45°). * **Clinical Correlation:** There is a strong association between *Aspergillus* and asthma, specifically in a condition known as **Allergic Bronchopulmonary Aspergillosis (ABPA)**. In ABPA, the fungus colonizes the bronchial tree, triggering a Type I (IgE-mediated) and Type III hypersensitivity reaction in asthmatic or cystic fibrosis patients. **2. Why the other options are incorrect:** * **Candida:** While it can cause pulmonary infections in severely immunocompromised hosts, it typically presents as **budding yeast cells and pseudohyphae** (except *C. albicans*, which forms true hyphae/germ tubes). It is not classically associated with asthma. * **Mucor:** These belong to the Zygomycetes family and are characterized by **broad, aseptate (coenocytic) hyphae** with right-angle (90°) branching. They typically cause Rhino-orbito-cerebral mucormycosis in diabetic patients. * **Cryptococcus:** This is an **encapsulated yeast** (not hyphal). It is identified using India Ink and is most commonly associated with meningitis in HIV patients. **3. NEET-PG High-Yield Pearls:** * **ABPA Diagnostic Criteria:** Look for asthma, fleeting pulmonary opacities, peripheral eosinophilia, and very high serum IgE levels (>1000 IU/mL). * **Culture:** *Aspergillus* grows on Sabouraud Dextrose Agar (SDA), producing "smoky green" colonies (*A. fumigatus*). * **Microscopy:** The fruiting body consists of a conidiophore ending in a swollen vesicle covered with sterigmata (phialides).

Question 255: A diabetic patient presents with pus from the eye. Colonies of the isolated organism are black with microscopic features of non-septate hyphae and obtuse branching. What is the diagnosis?

A. Aspergillosis
B. Candidiasis
C. Mucormycosis (Correct Answer)
D. Histoplasmosis

Explanation: ### Explanation **1. Why Mucormycosis is the Correct Answer:** The diagnosis is based on a combination of clinical presentation and classic morphological features: * **Clinical Context:** Diabetes mellitus (especially with ketoacidosis) is the most significant risk factor for **Rhino-oculo-cerebral Mucormycosis**. * **Microscopic Morphology:** The hallmark of Mucorales (e.g., *Rhizopus*, *Mucor*) is **broad, non-septate (coenocytic) hyphae** with **obtuse-angle (90°) branching**. * **Gross Appearance:** These fungi grow rapidly as "lid-lifters" with a cottony texture that turns **black/greyish** due to the production of pigmented sporangia. **2. Why Other Options are Incorrect:** * **Aspergillosis:** Characterized by **septate hyphae** with **acute-angle (45°) branching**. While it can cause ocular infections, the branching pattern described is pathognomonic for Mucormycosis. * **Candidiasis:** Typically presents as **budding yeast cells** and **pseudohyphae**. It does not form non-septate hyphae or black colonies with obtuse branching. * **Histoplasmosis:** A dimorphic fungus that exists as small, intracellular yeasts within macrophages at body temperature. It does not present with the described hyphal morphology. **3. NEET-PG High-Yield Pearls:** * **Angioinvasion:** Mucorales have a predilection for invading blood vessels, leading to thrombosis and tissue necrosis (black eschar). * **Specimen Handling:** Never grind or homogenize the tissue biopsy for Mucor; it destroys the fragile non-septate hyphae. Always use **tease mount** or **mincing**. * **Drug of Choice:** Liposomal **Amphotericin B** is the gold standard treatment, along with aggressive surgical debridement. * **Stains:** Best visualized using KOH mount, Calcofluor white, or silver stains (GMS).

Question 256: Which of the following methods allows for rapid evaluation of fungal hyphae and spores?

A. Grocott Gomori Methenamine silver stain
B. Hematoxylin and Eosin stain
C. Potassium hydroxide (KOH) wet mount (Correct Answer)
D. Periodic Acid Schiff stain

Explanation: **Explanation:** The correct answer is **C. Potassium hydroxide (KOH) wet mount.** **1. Why KOH Wet Mount is Correct:** The KOH mount is the **gold standard for rapid bedside evaluation** of fungal elements. When a clinical sample (skin scrapings, hair, or nails) is treated with 10–20% KOH, the strong alkali digests the keratin and cellular debris without affecting the fungal cell walls (which contain chitin). This "clearing" effect makes the fungal hyphae, spores, and budding yeast cells highly refractile and easily visible under a light microscope within minutes. **2. Why Other Options are Incorrect:** * **A. Grocott Gomori Methenamine Silver (GMS):** While this is the best stain for visualizing fungal morphology (staining them black), it is a complex histological process that takes hours to perform. It is not a "rapid" evaluation tool. * **B. Hematoxylin and Eosin (H&E):** This is a routine tissue stain. Many fungi are poorly visualized or appear pale/negative on H&E, making it unreliable for primary fungal screening. * **D. Periodic Acid Schiff (PAS):** This stain highlights the polysaccharides in the fungal cell wall (staining them bright pink/magenta). Like GMS, it is a laboratory-based histological stain and not a rapid point-of-care test. **Clinical Pearls for NEET-PG:** * **Modified KOH:** Adding **Calcofluor White** (a fluorescent dye) to the KOH mount enhances sensitivity by binding to cellulose/chitin, making fungi fluoresce under UV light. * **Tinea Versicolor:** KOH mount typically shows the characteristic **"Spaghetti and Meatball"** appearance (short hyphae and yeast clusters). * **Safety:** KOH is used specifically for specimens rich in keratin; for mucoid specimens like sputum, it acts as a mucolytic agent.

Question 257: Which of the following statements about Pneumocystis jiroveci is false?

A. It is primarily seen in immunocompromised individuals.
B. Ampicillin is the drug of choice for treatment. (Correct Answer)
C. It may be associated with pneumatocele formation.
D. It can be diagnosed with sputum microscopy.

Explanation: **Explanation:** *Pneumocystis jirovecii* (formerly *P. carinii*) is a unique unicellular fungus that lacks ergosterol in its cell membrane, making it resistant to standard antifungal agents like Amphotericin B. **Why Option B is the Correct Answer (False Statement):** The drug of choice for *Pneumocystis* pneumonia (PCP) is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, not Ampicillin. Ampicillin is a beta-lactam antibiotic used for bacterial infections and has no activity against fungi. In patients with sulfonamide allergies, alternative treatments include Pentamidine or Clindamycin-Primaquine. **Analysis of Other Options:** * **Option A:** It is an **opportunistic pathogen**. It is the most common opportunistic infection in HIV/AIDS patients (typically when CD4 counts fall below 200 cells/µL) and those on long-term immunosuppressants. * **Option C:** Radiologically, PCP typically presents with bilateral ground-glass opacities. However, it is well-known for causing **pneumatoceles** (thin-walled air-filled cysts), which can rupture leading to spontaneous pneumothorax. * **Option D:** Diagnosis can be made via microscopy of **induced sputum** or Bronchoalveolar Lavage (BAL). Since the organism cannot be cultured, stains like **Gomori Methenamine Silver (GMS)**—which highlights crushed-ping-pong-ball shaped cysts—or Direct Fluorescent Antibody (DFA) testing are used. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Previously classified as a protozoan, now classified as a **fungus** based on nucleic acid analysis. * **Stains:** GMS (best for cysts), Giemsa (for trophozoites), and Toluidine blue O. * **Serum Marker:** Elevated **Beta-D-Glucan** levels are often seen (non-specific but suggestive). * **Prophylaxis:** Indicated in HIV patients when CD4 count is **<200 cells/µL**.

Question 258: What is the most common cause of bronchopulmonary aspergillosis?

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

Explanation: ### Explanation **Correct Answer: A. Aspergillus fumigatus** **1. Why it is correct:** *Aspergillus fumigatus* is the most common species implicated in all forms of aspergillosis, including **Allergic Bronchopulmonary Aspergillosis (ABPA)**. It is a ubiquitous saprophytic fungus with small, thermotolerant spores (conidia) that are easily inhaled into the lower respiratory tract. In susceptible individuals (typically those with asthma or cystic fibrosis), these spores germinate into hyphae, triggering a complex Type I (IgE-mediated) and Type III (IgG-mediated) hypersensitivity reaction, leading to airway inflammation and bronchiectasis. **2. Why the other options are incorrect:** * **Aspergillus clavatus:** While it can cause hypersensitivity pneumonitis (specifically "Malt worker’s lung"), it is a rare cause of ABPA. * **Aspergillus flavus:** This is the second most common clinical isolate. It is more frequently associated with invasive aspergillosis in immunocompromised patients and **paranasal sinus infections**, but it is less common than *A. fumigatus* in ABPA. * **Aspergillus niger:** Characterized by black conidia, it is a common cause of **otomycosis** (fungal ear infection) and aspergilloma, but rarely triggers the specific allergic response seen in ABPA. **3. High-Yield Clinical Pearls for NEET-PG:** * **ABPA Diagnosis:** Look for the triad of **Asthma**, **Eosinophilia**, and **Fleeting pulmonary opacities** on X-ray. * **Radiology:** "Finger-in-glove" appearance due to mucoid impaction and central bronchiectasis. * **Laboratory:** Elevated total serum IgE (>1000 IU/mL) and specific IgE/IgG against *A. fumigatus*. * **Morphology:** *Aspergillus* species show **septate hyphae** with **dichotomous branching at acute angles (45°)**. * **Treatment:** Oral corticosteroids (to reduce inflammation) and Itraconazole (to reduce fungal load).

Question 259: All the following fungi produce mycotic keratitis except?

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

Explanation: **Explanation:** Mycotic keratitis (fungal corneal ulcer) is a serious ocular infection typically following ocular trauma involving vegetable matter or soil. The most common causative agents are **filamentous fungi (molds)** and **yeasts**. **Why Rhizopus is the correct answer:** * **Rhizopus** is a member of the order Mucorales. These fungi are primarily associated with **Rhinocerebral Mucormycosis**, especially in patients with uncontrolled diabetes mellitus or ketoacidosis. While they can involve the orbit (causing proptosis and ophthalmoplegia), they are **not** a standard cause of primary mycotic keratitis. **Analysis of Incorrect Options:** * **Aspergillus (A & B):** *Aspergillus fumigatus* and *Aspergillus niger* are among the most common causes of fungal keratitis worldwide. They typically present with "feathery" borders and satellite lesions on the cornea. * **Fusarium (C):** This is the **most common cause** of mycotic keratitis globally, particularly in tropical regions and among contact lens users. It is known for its rapid progression and resistance to many antifungal agents. **NEET-PG High-Yield Pearls:** 1. **Most common cause of Mycotic Keratitis:** *Fusarium* species (followed by *Aspergillus*). 2. **Most common cause in temperate climates/post-surgery:** *Candida albicans*. 3. **Clinical Sign:** Presence of **satellite lesions** and a "dry, immune ring" (Wessely ring) are characteristic of fungal ulcers. 4. **Diagnosis:** Gold standard is corneal scraping followed by **KOH mount** (shows hyphae) and culture on **Sabouraud Dextrose Agar (SDA)**. 5. **Treatment of choice:** Topical **Natamycin** (5%) is the first-line antifungal for filamentous fungal keratitis.

Question 260: Which of the following antibiotics is added to Sabouraud's dextrose agar to inhibit the growth of contaminating bacteria?

A. Gentamicin
B. Chloramphenicol (Correct Answer)
C. Penicillin
D. Doxycycline

Explanation: **Explanation:** **Sabouraud’s Dextrose Agar (SDA)** is the standard medium used for the isolation and cultivation of fungi. Because fungi grow slowly compared to bacteria, clinical specimens (like skin scrapings or sputum) often contain rapidly growing bacterial flora that can overgrow and mask fungal colonies. 1. **Why Chloramphenicol is the Correct Answer:** Chloramphenicol is the most common antibiotic added to SDA to make it **selective**. It is preferred because it has a **broad spectrum of activity** against both Gram-positive and Gram-negative bacteria, is **heat-stable** (allowing it to be autoclaved with the media), and does not inhibit the growth of most pathogenic fungi. 2. **Analysis of Incorrect Options:** * **Gentamicin (Option A):** While sometimes used in combination with chloramphenicol to enhance the inhibition of certain Gram-negative bacteria (like *Pseudomonas*), it is not the classic or primary single additive associated with standard SDA in most textbook descriptions. * **Penicillin (Option C):** Historically used in early formulations, but it is less stable and has a narrower spectrum compared to chloramphenicol. * **Doxycycline (Option D):** Not used in standard mycological media as it is less effective than chloramphenicol at suppressing the wide range of environmental contaminants found in clinical samples. **High-Yield Clinical Pearls for NEET-PG:** * **SDA Composition:** It has a low pH (~5.6) which inherently inhibits many bacteria, but antibiotics are added for further selectivity. * **Cycloheximide (Actidione):** Often added alongside chloramphenicol to inhibit **saprophytic fungi** (contaminants). Note: Cycloheximide can inhibit certain pathogens like *Cryptococcus neoformans* and *Aspergillus*. * **Emmons’ Modification:** A version of SDA with neutral pH and lower glucose to support better growth of certain fungi. * **Dermatophyte Test Medium (DTM):** Contains phenol red; dermatophytes turn the medium **red** due to alkaline metabolite production.

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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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