Mycology Practice Questions

Q: Candida albicans can be differentiated from other Candida species on cornmeal agar by its unique ability to form which of the following?

Chlamydospores. ### Explanation **Correct Option: C. Chlamydospores** *Candida albicans* is uniquely identified on **Cornmeal Agar (CMA)** by the production of **thick-walled, terminal resting spores called Chlamydospores**. CMA is a nutritionally deficient medium that induces stress in the fungus, stimulating the formation of these characteristic structures. This is a definitive morphological test used in laboratories to differentiate *C. albicans* (and the closely related *C. dubliniensis*) from other non-albicans species. **Analysis of Incorrect Options:** * **A. Aseptate hyphae:** These are characteristic of Zygomycetes (e.g., *Rhizopus*, *Mucor*). *Candida* species are yeasts that produce septate pseudohyphae and true hyphae. * **B. Germ tubes:** While the **Germ Tube Test (Reynolds-Braude phenomenon)** is a rapid diagnostic test for *C. albicans*, it is performed using **human or rabbit serum** incubated at 37°C for 2–3 hours, not on cornmeal agar. * **D. Arthrospores:** These are formed by the fragmentation of hyphae and are characteristic of fungi like *Trichosporon* and *Geotrichum candidum*, but not *Candida*. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** The earliest morphological change in *C. albicans* when shifted from 25°C to 37°C in serum. * **Phenotypic Switching:** *C. albicans* can switch between yeast (commensal) and hyphal (pathogenic/invasive) forms. * **C. dubliniensis:** The only other species that produces chlamydospores and is germ tube positive; it is typically differentiated by its inability to grow at 45°C. * **CHROMagar:** A specialized differential medium where *C. albicans* produces characteristic **light green** colonies.

Q: An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following conditions?

Aspergillosis. **Explanation:** The correct answer is **Aspergillosis**. **Why Aspergillosis is correct:** *Aspergillus* species are filamentous fungi characterized by the presence of **septate hyphae** that typically show **dichotomous branching at acute angles (45°)**. In clinical practice, when *Aspergillus* involves the lungs (such as in an Aspergilloma or Invasive Pulmonary Aspergillosis), these characteristic hyphae can be directly visualized in the sputum or bronchoalveolar lavage (BAL) fluid using KOH mounts or silver stains. **Analysis of Incorrect Options:** * **Sporotrichosis:** Caused by *Sporothrix schenckii*, a dimorphic fungus. In tissue or clinical samples (yeast phase), it typically appears as **cigar-shaped budding yeasts**, not hyphae. * **Histoplasmosis:** *Histoplasma capsulatum* is an intracellular dimorphic fungus. In sputum or tissue, it is seen as **small, oval budding yeasts** within macrophages. Hyphae are only seen in the mold form at room temperature in the lab. * **Cryptococcosis:** *Cryptococcus neoformans* is a monomorphic yeast. It is characterized by **spherical, encapsulated budding yeasts**. It never forms true hyphae; its hallmark is the thick polysaccharide capsule visualized by India Ink. **NEET-PG High-Yield Pearls:** * **Aspergillus:** Look for "Acute angle branching" and "Septate hyphae." * **Mucor/Rhizopus:** Look for "Right angle (90°) branching" and "Aseptate/Coenocytic hyphae." * **Dimorphic Fungi Rule:** They exist as **M**old in the **C**old (25°C - hyphae) and **Y**east in the **B**east (37°C/Body - yeast). Since sputum is a clinical sample from the body, you expect the yeast form for *Sporothrix* and *Histoplasma*.

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

Coccidioides immitis. ### 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).

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

Aspergillus. ### 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).

Q: 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?

Mucormycosis. ### 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).

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

Ampicillin is the drug of choice for treatment.. **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**.

Q: What is the most common cause of bronchopulmonary aspergillosis?

Aspergillus fumigatus. ### 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).

Q: All the following fungi produce mycotic keratitis except?

Rhizopus. **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.

Q: Which of the following is NOT true about Histoplasma capsulatum?

It is capsulated.. The correct answer is **C (It is capsulated)**. ### **Explanation** Despite its name, *Histoplasma capsulatum* is **not a capsulated fungus**. The name is a historical misnomer; when first discovered, the clear halo seen around the yeast cells in tissue sections was mistaken for a capsule. In reality, this halo is an artifact caused by the shrinkage of the cytoplasm away from the cell wall during fixation. The only clinically significant fungus that is truly capsulated is *Cryptococcus neoformans*. ### **Analysis of Other Options** * **A. It is a dimorphic fungus:** This is true. It exists as a **mold** in the environment (soil enriched with bird/bat droppings) and as an **intracellular yeast** at body temperature (37°C). * **B. It may mimic Tuberculosis:** This is true. Chronic pulmonary histoplasmosis presents with cough, fever, night sweats, and cavitary lesions in the upper lobes of the lungs, making it clinically and radiologically indistinguishable from TB. * **C. It is mostly asymptomatic:** This is true. In endemic areas, the majority of infections in immunocompetent individuals are subclinical or present as a self-limiting flu-like illness. ### **High-Yield Clinical Pearls for NEET-PG** * **Habitat:** Soil enriched with **bird (starling) or bat droppings** (caves/chicken coops). * **Microscopy:** Look for **tuberculate macroconidia** (thick-walled with finger-like projections) in the mold form. * **Intracellular nature:** It is an obligate intracellular parasite of **macrophages**. * **Diagnosis:** Skin test (Histoplasmin) is used for epidemiological studies; Antigen detection (Urinary/Serum) is best for disseminated cases. * **Treatment:** Itraconazole for mild cases; Amphotericin B for severe/disseminated disease.

Q: Otomycosis is most commonly caused by which organism?

Aspergillus. **Explanation:** **Otomycosis** (Otitis Externa Mycotica) is a fungal infection of the external auditory canal, typically occurring in hot, humid climates or following prolonged use of topical antibiotic ear drops which disrupt the normal bacterial flora. **Why Aspergillus is correct:** * **Aspergillus niger** is the most common causative organism (responsible for ~80% of cases). It is clinically characterized by a "wet newspaper" appearance or a black, sooty mass of fungal debris (black spores). * **Aspergillus fumigatus** is the second most common, often presenting with pale blue or greenish spores. **Why the other options are incorrect:** * **Candida albicans:** While it is the second most common genus involved in otomycosis, it is less frequent than Aspergillus. It typically presents as a white, creamy, curd-like discharge. * **Mucormycosis:** This is an invasive, life-threatening fungal infection (Rhino-oculo-cerebral) usually seen in immunocompromised or diabetic patients. It does not typically cause routine otomycosis. * **Histoplasmosis:** This is a systemic fungal infection primarily affecting the lungs; it is not a standard cause of external ear infections. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Symptom:** Intense itching (pruritus) is the hallmark, followed by ear pain and deafness if the canal is obstructed. * **Otoscopy:** Look for the "Wet Newspaper" appearance. * **Treatment:** 1. Thorough **ear toilet** (suction/mopping) is the most crucial step. 2. Topical antifungal agents (e.g., Clotrimazole, Nystatin). 3. Keeping the ear dry. * **Key Association:** Overuse of antibiotic-steroid ear drops is a major predisposing factor.

Question 1

Candida albicans can be differentiated from other Candida species on cornmeal agar by its unique ability to form which of the following?

Accepted Answer

Chlamydospores

Answer

Aseptate hyphae

Answer

Germ tubes

Answer

Arthrospores

Question 2

An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following conditions?

Accepted Answer

Aspergillosis

Answer

Sporotrichosis

Answer

Histoplasmosis

Answer

Cryptococcosis

Question 3

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

Accepted Answer

Coccidioides immitis

Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Aspergillus

Question 4

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

Accepted Answer

Aspergillus

Answer

Candida

Answer

Mucor

Answer

Cryptococcus

Question 5

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?

Accepted Answer

Mucormycosis

Answer

Aspergillosis

Answer

Candidiasis

Answer

Histoplasmosis

Question 6

Which of the following statements about Pneumocystis jiroveci is false?

Accepted Answer

Ampicillin is the drug of choice for treatment.

Answer

It is primarily seen in immunocompromised individuals.

Answer

It may be associated with pneumatocele formation.

Answer

It can be diagnosed with sputum microscopy.

Question 7

What is the most common cause of bronchopulmonary aspergillosis?

Accepted Answer

Aspergillus fumigatus

Answer

Aspergillus clavatus

Answer

Aspergillus flavus

Answer

Aspergillus niger

Question 8

All the following fungi produce mycotic keratitis except?

Accepted Answer

Rhizopus

Answer

Aspergillus niger

Answer

Aspergillus fumigatus

Answer

Fusarium

Question 9

Which of the following is NOT true about Histoplasma capsulatum?

Accepted Answer

It is capsulated.

Answer

It is a dimorphic fungus.

Answer

It may mimic Tuberculosis.

Answer

It is mostly asymptomatic.

Question 10

Otomycosis is most commonly caused by which organism?

Accepted Answer

Aspergillus

Answer

Candida Albicans

Answer

Mucormycosis

Answer

Histoplasmosis

Mycology — MCQs

Mycology — MCQs

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