Mycology Practice Questions

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.

Q: Which of the following microorganisms presents as capsulated yeast?

Cryptococcus. ### Explanation **Correct Answer: C. Cryptococcus** The defining characteristic of *Cryptococcus neoformans* is its **prominent polysaccharide capsule** (composed of glucuronoxylomannan). In medical mycology, it is the only medically important fungus that exists as a **capsulated yeast** both in the environment and in host tissues. This capsule is a major virulence factor as it inhibits phagocytosis. On microscopy, it appears as a round-to-oval budding yeast; the capsule is best visualized using **India Ink** (negative staining), where it appears as a clear halo against a dark background. **Analysis of Incorrect Options:** * **A. Histoplasma:** This is a **dimorphic fungus**. In tissue, it presents as small, intracellular yeast cells (found within macrophages). While it may appear to have a "halo" due to shrinkage during staining, it lacks a true capsule (hence the name *Histoplasma capsulatum* is a misnomer). * **B. Candida:** This is a **yeast-like fungus** that produces pseudohyphae and blastoconidia. It is non-capsulated. The most common species, *C. albicans*, is identified by the Germ Tube test. * **C. Sporothrix:** Another **dimorphic fungus** (causing "Rose gardener’s disease"). In tissue, it appears as cigar-shaped yeast cells, not capsulated forms. **NEET-PG High-Yield Pearls:** * **Stains for Capsule:** India Ink (screening), Nigrosin, and **Mucicarmine** (specific stain that colors the capsule red). * **Antigen Detection:** Latex Agglutination test for cryptococcal polysaccharide antigen (CrAg) is more sensitive than India Ink for CSF diagnosis. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white mucoid colonies. It is **Urease positive**. * **Clinical Association:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100 cells/µL).

Q: A woman who pricked her finger while pruning rose bushes develops a local pustule that progressed to an ulcer. Several nodules then developed along the local lymphatic drainage. What is the most likely etiological agent?

Sporothrix schenkii. ### Explanation **Correct Option: D. Sporothrix schenkii** The clinical presentation described is a classic case of **Sporotrichosis**, often referred to as **"Rose Gardener’s Disease."** * **Mechanism:** *Sporothrix schenkii* is a **dimorphic fungus** found in soil, moss, and decaying vegetation (like rose bushes). Infection occurs via **traumatic inoculation** (e.g., a thorn prick). * **Clinical Progression:** It typically begins as a painless papule or pustule at the site of injury, which eventually ulcerates. The hallmark of this infection is **lymphocutaneous spread**, where secondary nodules develop sequentially along the lines of lymphatic drainage (sporotrichoid spread). **Why other options are incorrect:** * **A. Aspergillus fumigatus:** Primarily causes respiratory infections (Allergic Bronchopulmonary Aspergillosis or Aspergilloma) in immunocompromised hosts; it does not typically present with lymphocutaneous nodules. * **B. Candida albicans:** Usually causes opportunistic infections like oral thrush, vaginal candidiasis, or intertrigo. It does not follow a lymphatic distribution after skin trauma. * **C. Histoplasma capsulatum:** A systemic dimorphic fungus primarily acquired through inhalation of bird/bat droppings. It causes pulmonary disease and does not typically present with localized lymphatic nodules following a skin prick. **High-Yield NEET-PG Pearls:** 1. **Morphology:** It is a **dimorphic fungus**. At 25°C (mold), it shows "daisy-wheel" or **flower-like sporulation**. At 37°C (yeast), it appears as **cigar-shaped bodies**. 2. **Histopathology:** May show **Asteroid bodies** (Splendore-Hoeppli phenomenon). 3. **Treatment:** The drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used. 4. **Differential Diagnosis:** Other causes of "sporotrichoid spread" include *Mycobacterium marinum*, *Nocardia*, and *Leishmania brasiliensis*.

Q: A patient with AIDS presents with dyspnea and respiratory illness. Which of the following investigations is most suitable to diagnose the opportunistic infection commonly seen in AIDS patients?

Bronchoalveolar lavage. **Explanation:** The clinical presentation of dyspnea and respiratory illness in an AIDS patient strongly suggests **Pneumocystis jirovecii pneumonia (PCP)**, the most common opportunistic respiratory infection in this population. **Why Bronchoalveolar Lavage (BAL) is the correct answer:** *Pneumocystis jirovecii* is an atypical fungus (formerly classified as a parasite) that cannot be cultured. Diagnosis relies on the microscopic visualization of cysts or trophozoites in respiratory specimens. **BAL is the gold standard** diagnostic procedure because it has a very high sensitivity (>90–95%) for detecting the organism, as it samples the alveolar spaces where the pathogen primarily resides. **Analysis of Incorrect Options:** * **Chest X-ray (A):** While often the first investigation, it typically shows non-specific bilateral perihilar interstitial infiltrates ("ground-glass appearance"). It is a screening tool, not a definitive diagnostic test. * **CT scan (B):** High-resolution CT (HRCT) is highly sensitive for detecting early interstitial changes but lacks the specificity to differentiate PCP from other opportunistic infections like CMV or MAI. * **Sputum microscopy (C):** Spontaneous sputum has very low sensitivity because *P. jirovecii* is not easily expectorated. While **induced sputum** (using hypertonic saline) is a valid initial step, BAL remains the most suitable and definitive investigation when sputum is negative or unavailable. **NEET-PG High-Yield Pearls:** * **Stains of choice:** Gomori Methenamine Silver (GMS) stain (shows crushed-cup/boat-shaped cysts) and Direct Fluorescent Antibody (DFA) testing. * **Prophylaxis:** Started when CD4 count falls below **200 cells/mm³**. Drug of choice is **TMP-SMX**. * **Biomarker:** Elevated serum **Beta-D-Glucan** is a highly sensitive but non-specific marker for PCP.

Q: In a patient with HIV infection, oral ulcer is most commonly due to which of the following?

Candida. **Explanation:** **1. Why Candida is Correct:** Oral Candidiasis (Thrush) is the **most common opportunistic fungal infection** in HIV-positive individuals. It often serves as an early clinical marker of HIV progression and typically occurs when the CD4 count falls below **200-300 cells/mm³**. The most common causative agent is *Candida albicans*. Clinically, it presents as pseudomembranous (white curd-like plaques that can be scraped off), erythematous (atrophic), or angular cheilitis. **2. Why the Other Options are Incorrect:** * **Cryptococcosis:** While *Cryptococcus neoformans* is a major cause of fungal meningitis in HIV patients (usually CD4 <100), it rarely presents with primary oral ulcers. Cutaneous/mucosal lesions are usually secondary to systemic dissemination. * **Histoplasma:** *Histoplasma capsulatum* can cause chronic, painful oral ulcers in HIV patients, but it is much less common than Candida. It typically occurs in the late stages of AIDS (CD4 <150) and represents disseminated disease. * **Trichophyton:** This is a dermatophyte responsible for superficial infections like Tinea corporis or Tinea pedis. It involves keratinized tissue (skin, hair, nails) and does not typically cause oral mucosal ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Most common oral manifestation of HIV:** Oral Candidiasis. * **Most common site for Oral Candidiasis:** Buccal mucosa and tongue. * **Treatment of choice:** Topical Nystatin or Clotrimazole for mild cases; Oral **Fluconazole** for moderate-to-severe or esophageal involvement. * **Esophageal Candidiasis:** An AIDS-defining illness (CD4 <100). * **Differential Diagnosis:** Oral Hairy Leukoplakia (caused by **EBV**), which presents as white corrugated patches on the lateral borders of the tongue that **cannot** be scraped off.

Q: All of the following are associated with zygomycosis except?

Candida. **Explanation:** Zygomycosis (now more commonly referred to as **Mucormycosis**) is a life-threatening opportunistic infection caused by fungi belonging to the order **Mucorales** (Class: Zygomycetes). **1. Why Candida is the correct answer:** **Candida** is a yeast-like fungus belonging to the Phylum Ascomycota. It causes Candidiasis, not zygomycosis. Unlike the Mucorales group, Candida typically presents as budding yeast cells and pseudohyphae on microscopy. **2. Why the other options are incorrect:** * **Rhizopus:** The most common genus causing human mucormycosis (especially the rhino-cerebral form in diabetics). It is characterized by the presence of rhizoids (root-like structures) located directly opposite the sporangiophores. * **Mucor:** A classic genus of the Mucorales order. Unlike Rhizopus, it lacks rhizoids. * **Lichtheimia (formerly Absidia):** Another significant cause of zygomycosis. It is distinguished by having rhizoids located between the sporangiophores (internodal). **Clinical Pearls for NEET-PG:** * **Microscopy:** Zygomycetes are characterized by **broad, ribbon-like, aseptate (or sparsely septate) hyphae** with **wide-angled (90°) branching**. (Contrast this with *Aspergillus*, which has narrow, septate hyphae with acute-angled branching). * **Risk Factors:** Uncontrolled Diabetes Mellitus (Diabetic Ketoacidosis), neutropenia, and iron overload (deferoxamine therapy). * **Clinical Hallmark:** Tissue infarction and necrosis due to **angioinvasion**. * **Treatment:** Surgical debridement and **Liposomal Amphotericin B** are the treatments of choice. Posaconazole or Isavuconazole are used as step-down or salvage therapy.

Q: Which of the following is the most common etiological agent in paranasal sinus mycosis?

Aspergillus fumigatus. **Explanation:** **Aspergillus fumigatus** is the most common etiological agent of paranasal sinus mycosis (Fungal Rhinosinusitis). This is due to the ubiquitous nature of its spores in the environment and their small size (2–3 µm), which allows them to be easily inhaled and deposited in the paranasal sinuses. It can manifest in several forms, ranging from non-invasive (Fungal Ball or Allergic Fungal Rhinosinusitis) to life-threatening invasive disease, especially in immunocompromised patients. **Analysis of Incorrect Options:** * **Histoplasma:** While *Histoplasma capsulatum* is a systemic dimorphic fungus, it primarily causes pulmonary infections. Sinus involvement is rare and usually occurs only as part of a disseminated infection in severely immunocompromised individuals. * **Conidiobolus coronatus:** This is the agent of **Entomophthoromycosis**. While it causes chronic subcutaneous swelling of the nose and facial soft tissues (rhinofacial zygomycosis), it is much less common than Aspergillosis and typically restricted to tropical climates. * **Candida albicans:** Although a common human commensal, *Candida* is an infrequent cause of primary fungal sinusitis. It is more commonly associated with oral thrush or systemic candidiasis. **High-Yield Clinical Pearls for NEET-PG:** * **Allergic Fungal Rhinosinusitis (AFRS):** The most common form of fungal sinusitis; characterized by "peanut butter" like thick mucus (allergic mucin) containing Charcot-Leyden crystals. * **Morphology:** On microscopy, *Aspergillus* shows **septate hyphae** with **dichotomous branching at acute angles (45°)**. * **Mucormycosis:** A critical differential in diabetics; characterized by broad, **aseptate hyphae** with **right-angle branching (90°)**.

Question 1

All the following fungi produce mycotic keratitis except?

Accepted Answer

Rhizopus

Answer

Aspergillus niger

Answer

Aspergillus fumigatus

Answer

Fusarium

Question 2

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 3

Otomycosis is most commonly caused by which organism?

Accepted Answer

Aspergillus

Answer

Candida Albicans

Answer

Mucormycosis

Answer

Histoplasmosis

Question 4

Which of the following microorganisms presents as capsulated yeast?

Accepted Answer

Cryptococcus

Answer

Histoplasma

Answer

Candida

Answer

Sporothrix

Question 5

A woman who pricked her finger while pruning rose bushes develops a local pustule that progressed to an ulcer. Several nodules then developed along the local lymphatic drainage. What is the most likely etiological agent?

Accepted Answer

Sporothrix schenkii

Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Histoplasma capsulatum

Question 6

A patient with AIDS presents with dyspnea and respiratory illness. Which of the following investigations is most suitable to diagnose the opportunistic infection commonly seen in AIDS patients?

Accepted Answer

Bronchoalveolar lavage

Answer

Chest X-ray

Answer

CT scan of the chest

Answer

Sputum microscopy

Question 7

In a patient with HIV infection, oral ulcer is most commonly due to which of the following?

Accepted Answer

Candida

Answer

Cryptococcosis

Answer

Histoplasma

Answer

Trichophyton

Question 8

Which of the following is NOT true of Candida albicans?

Accepted Answer

Blastoconidia are seen in isolates.

Answer

It is a yeast-like fungus.

Answer

It forms chlamydospores.

Answer

It can cause meningitis in immunocompromised individuals.

Question 9

All of the following are associated with zygomycosis except?

Accepted Answer

Candida

Answer

Mucor

Answer

Rhizopus

Answer

Lichthemia

Question 10

Which of the following is the most common etiological agent in paranasal sinus mycosis?

Accepted Answer

Aspergillus fumigatus

Answer

Histoplasma

Answer

Conidiobolus coronatus

Answer

Candida albicans

Mycology — MCQs

Mycology — MCQs

On this page

Practice by Chapter

Want unlimited practice?