Mycology Practice Questions

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°)**.

Q: As a coordinator for the construction of a bone marrow transplant unit (BMTU), you are overseeing extensive modifications including the removal of walls and floors to install laminar flow rooms. Considering both frequency and lethality, which of the following fungi should be the primary concern?

Aspergillus species. **Explanation:** The correct answer is **Aspergillus species**. **1. Why Aspergillus is the primary concern:** The scenario describes a high-risk environment (Bone Marrow Transplant Unit) undergoing **construction and renovation**. *Aspergillus* spores (conidia) are ubiquitous in the environment, particularly in dust, soil, and decomposing organic matter. Construction activities like removing walls and floors aerosolize these spores. Immunocompromised patients, especially those with prolonged neutropenia following a BMT, are at extreme risk of **Invasive Aspergillosis (IA)** via inhalation. IA has a high mortality rate (lethality) in this population, making environmental control (HEPA filters and laminar airflow) mandatory. **2. Why other options are incorrect:** * **Candida species:** While *Candida* is a frequent cause of nosocomial fungal infections, it is typically **endogenous** (part of the patient's own flora) or transmitted via direct contact/catheters. It is not an airborne fungus associated with construction dust. * **Cryptococcus species:** *Cryptococcus neoformans* is typically associated with pigeon droppings and primarily affects HIV/AIDS patients (meningitis). It is not the leading concern during hospital renovations. * **Penicillium species:** While common in the environment, most species are non-pathogenic contaminants. *Talaromyces (Penicillium) marneffei* is a pathogen but is geographically restricted and not specifically linked to construction-related outbreaks in BMTUs. **Clinical Pearls for NEET-PG:** * **High-yield trigger:** Construction/Renovation + Immunocompromised patient = **Aspergillus**. * **Prevention:** HEPA (High-Efficiency Particulate Air) filters are the gold standard for preventing IA in BMTUs. * **Diagnosis:** Look for "Dichotomous branching at 45° angles" and "Septate hyphae" on microscopy. * **Biomarker:** Galactomannan assay (cell wall component).

Q: A diabetic patient presents with bloody nasal discharge, orbital swelling, and pain. Culture of periorbital pus shows branching septate hyphae. Which of the following is the most probable organism involved?

Aspergillus. ### Explanation The clinical presentation of a diabetic patient with bloody nasal discharge, orbital swelling, and pain strongly suggests **Rhino-orbital-cerebral fungal infection**. The key to distinguishing the causative agent lies in the microscopic morphology. **1. Why Aspergillus is correct:** The definitive clue is the description of **"branching septate hyphae."** *Aspergillus* species are characterized by narrow, septate hyphae that branch at **acute angles (approximately 45°)**. While *Mucor* and *Rhizopus* are more common causes of rhino-orbital infections in uncontrolled diabetics (especially during ketoacidosis), they possess distinct morphology (non-septate). *Aspergillus* can also cause invasive rhinosinusitis in immunocompromised or diabetic individuals. **2. Why the other options are incorrect:** * **Mucor and Rhizopus (Options A & D):** These belong to the order Mucorales. They are characterized by **broad, ribbon-like, aseptate (non-septate) hyphae** that branch at **right angles (90°)**. Although the clinical scenario (diabetes) highly favors these organisms, the microscopic description of "septate hyphae" rules them out. * **Candida (Option B):** *Candida* typically presents as budding yeast cells and **pseudohyphae** (constrictions at septa). It does not typically cause the acute, invasive rhino-orbital clinical picture described. **Clinical Pearls for NEET-PG:** * **Aspergillus:** Septate hyphae, 45° branching, Fruiting bodies (in aerobic conditions), Conidiophores. * **Mucormycosis:** Aseptate hyphae, 90° branching, associated with **Diabetic Ketoacidosis (DKA)** due to the organism's ketone reductase enzyme. * **Treatment:** Amphotericin B is the drug of choice for invasive Mucormycosis, while Voriconazole is preferred for Invasive Aspergillosis. * **Silver Stain (GMS):** Used to highlight fungal morphology in tissue sections.

Question 1

Which of the following microorganisms presents as capsulated yeast?

Accepted Answer

Cryptococcus

Answer

Histoplasma

Answer

Candida

Answer

Sporothrix

Question 2

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 3

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 4

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 5

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 6

All of the following are associated with zygomycosis except?

Accepted Answer

Candida

Answer

Mucor

Answer

Rhizopus

Answer

Lichthemia

Question 7

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

Question 8

As a coordinator for the construction of a bone marrow transplant unit (BMTU), you are overseeing extensive modifications including the removal of walls and floors to install laminar flow rooms. Considering both frequency and lethality, which of the following fungi should be the primary concern?

Accepted Answer

Aspergillus species

Answer

Candida species

Answer

Cryptococcus species

Answer

Penicillium species

Question 9

A diabetic patient presents with bloody nasal discharge, orbital swelling, and pain. Culture of periorbital pus shows branching septate hyphae. Which of the following is the most probable organism involved?

Accepted Answer

Aspergillus

Answer

Mucor

Answer

Candida

Answer

Rhizopus

Question 10

Pneumocystis carinii is classified as a fungus because of which of the following characteristics?

Accepted Answer

rRNA, mitochondrial protein gene sequence, and presence of thymidylate synthase

Answer

Cell wall contains glucans

Answer

Antifungals are effective against P. carinii

Answer

It is the commonest opportunistic infection in AIDS patients

Mycology — MCQs

Mycology — MCQs

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