Mycology Practice Questions

Q: Barrel-shaped arthroconidia are characteristic of which one of the following fungi?

C. immitis. **Explanation:** The correct answer is **Coccidioides immitis**. **1. Why C. immitis is correct:** *Coccidioides immitis* is a dimorphic fungus that exists in nature (soil) as a mold. It produces highly infectious, thick-walled, **barrel-shaped arthroconidia** (arthrospores). A key diagnostic feature is that these arthroconidia alternate with empty "disjunctor cells," giving them a characteristic **"checkerboard" appearance** under the microscope. When inhaled by a human, these arthroconidia transform into large, thick-walled **spherules** containing endospores in the lungs. **2. Why the other options are incorrect:** * **Epidermophyton floccosum:** A dermatophyte characterized by large, smooth-walled, **club-shaped (pyriform) macroconidia** arranged in clusters (often compared to "beaver tails"). It does not produce barrel-shaped arthroconidia. * **Phialophora verrucosa:** One of the causative agents of Chromoblastomycosis. It is characterized by **vase-shaped phialides** with a distinct collarette, producing oval conidia. * **Microsporum canis:** A zoophilic dermatophyte known for its spindle-shaped, thick-walled **macroconidia with curved/hooked ends** and more than six internal cells. **3. NEET-PG High-Yield Pearls:** * **Coccidioidomycosis** is also known as **Valley Fever** or Desert Rheumatism (endemic to SW USA/Mexico). * **Safety Warning:** *C. immitis* is highly laboratory-contagious; cultures must be handled in a Biosafety Level 3 (BSL-3) facility. * **Diagnostic Triad:** Barrel-shaped arthroconidia (in vitro/soil) → Spherules with endospores (in vivo/tissue). * **E. floccosum** is unique among dermatophytes because it **never produces microconidia**.

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

It is frequently associated with Cytomegalovirus (CMV).. **Explanation:** *Pneumocystis jirovecii* (formerly *P. carinii*) is a unique unicellular fungus that primarily causes **Pneumocystis Pneumonia (PCP)** in immunocompromised hosts. **Why Option B is the Correct (False) Statement:** While both *P. jirovecii* and Cytomegalovirus (CMV) are common opportunistic infections in HIV/AIDS patients, there is **no specific or frequent pathological association** between the two. They are independent co-infections. The presence of one does not inherently necessitate or predict the presence of the other, making this statement the false one among the choices. **Analysis of Other Options:** * **Option A:** *P. jirovecii* is an opportunistic pathogen. It rarely causes disease in healthy individuals but is a defining illness in patients with low CD4 counts (<200 cells/µL), transplant recipients, or those on long-term steroids. * **Option C:** PCP is known for causing interstitial inflammation which can lead to subpleural blebs or **pneumatoceles** (air-filled cysts). Rupture of these cysts can lead to spontaneous pneumothorax, a known complication. * **Option D:** Diagnosis is primarily microscopic. While **induced sputum** can be used, it has lower sensitivity than Bronchoalveolar Lavage (BAL). Organisms are visualized using **Gomori Methenamine Silver (GMS)** stain (shows crushed-cup shaped cysts) or Direct Fluorescent Antibody (DFA) testing. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** It was previously classified as a protozoan but is now a **fungus** based on nucleic acid analysis (lacks ergosterol in the cell membrane). * **Drug of Choice:** **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Radiology:** Classic "Ground-glass opacities" (GGO) and perihilar infiltrates on X-ray/CT. * **Biomarker:** Elevated **Serum Beta-D-Glucan** is a sensitive but non-specific marker for PCP.

Q: Which organism is known to be capsulated?

Cryptococcus neoformans. **Explanation:** The correct answer is **Cryptococcus neoformans**. In microbiology, the capsule is a major virulence factor that inhibits phagocytosis. While many bacteria are capsulated, *Cryptococcus neoformans* is the **only medically important fungus** that possesses a prominent polysaccharide (glucuronoxylomannan) capsule. **Why the other options are incorrect:** * **Histoplasma capsulatum:** Despite its misleading name, this fungus is **not capsulated**. The name "capsulatum" was given by its discoverer, Samuel Darling, who mistakenly identified the halo around the yeast cells in tissue sections (an artifact of shrinkage) as a capsule. * **Neisseria gonorrhoeae:** Unlike its relative *Neisseria meningitidis* (which is heavily capsulated), *N. gonorrhoeae* is **non-capsulated**. It relies on pili and Opa proteins for virulence and attachment. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** The capsule of *Cryptococcus* is best visualized using **India Ink** or **Nigrosin** (negative staining), where it appears as a clear halo against a dark background. * **Biochemical Marker:** For tissue sections, **Mucicarmine stain** is specific for the Cryptococcal capsule (stains it bright red). * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test is a highly sensitive latex agglutination test used to detect the capsular polysaccharide in CSF or serum. * **Mnemonic for Capsulated Organisms:** "Some Killers Have Nice Shiny Bodies" (**S**trep pneumoniae, **K**lebsiella, **H**aemophilus influenzae, **N**eisseria meningitidis, **S**almonella typhi, **B**acillus anthracis—notably a polypeptide capsule).

Q: Tinea Nigra is caused by which organism?

Hortaea werneckii. **Explanation:** **Tinea Nigra** is a superficial fungal infection (superficial mycosis) characterized by asymptomatic, brown-to-black non-scaly macules, typically on the palms and soles. 1. **Why Option A is Correct:** The causative agent of Tinea Nigra is **Hortaea werneckii** (formerly known as *Exophiala werneckii*). It is a **dematiaceous** (pigmented) fungus that produces melanin, giving the clinical lesion its characteristic dark appearance. Diagnosis is confirmed by skin scrapings in KOH, which show branched, septate dark hyphae and elongated budding cells. 2. **Why Other Options are Incorrect:** * **B. Piedraia hortae:** This organism causes **Black Piedra**, a superficial infection of the hair shaft characterized by hard, black nodules. * **C. T. rubrum (Trichophyton rubrum):** This is a dermatophyte and the most common cause of Tinea corporis, Tinea pedis, and Onychomycosis. It involves deeper keratinized layers compared to Tinea Nigra. * **D. Microsporum:** This is a genus of dermatophytes that commonly causes Tinea capitis and Tinea corporis, often characterized by ectothrix hair involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Often misdiagnosed as malignant melanoma; however, Tinea Nigra is superficial and can be "scraped off." * **Transmission:** Usually occurs via traumatic inoculation from soil, sewage, or decaying vegetation. * **Culture:** On Sabouraud Dextrose Agar (SDA), it produces black, mucoid, yeast-like colonies. * **Treatment:** Topical antifungal creams (e.g., Whitfield ointment, imidazoles).

Q: Impaired immune competence is the predisposing factor in about half of all persons who develop which of the following fungal infections?

Cryptococcosis. **Explanation:** The correct answer is **Cryptococcosis**. **1. Why Cryptococcosis is correct:** *Cryptococcus neoformans* is considered a classic **opportunistic fungal pathogen**. While it can occasionally infect healthy individuals, approximately **50% to 80%** of clinically significant cases occur in patients with impaired cell-mediated immunity (CMI). The most common predisposing factor is HIV/AIDS (typically when CD4 counts are <100 cells/µL), followed by organ transplant recipients, patients on chronic corticosteroids, and those with hematological malignancies. The fungus is inhaled but requires a weakened immune system to disseminate, most commonly causing meningoencephalitis. **2. Why the other options are incorrect:** * **A, B, and C (Histoplasmosis, Coccidioidomycosis, and Blastomycosis):** These are classified as **Systemic (Endemic) Mycoses**. Unlike opportunistic fungi, these are **primary pathogens**, meaning they are inherently virulent and can cause significant disease in **immunocompetent** individuals who inhale a sufficient fungal load. While immunosuppression can lead to more severe or disseminated forms of these diseases, the majority of infections occur in healthy hosts living in endemic geographical regions. **3. NEET-PG High-Yield Pearls:** * **Source:** Pigeon droppings and contaminated soil. * **Virulence Factor:** The **Polysaccharide capsule** (inhibits phagocytosis) is the most important. * **Diagnosis:** * **India Ink:** Shows a clear halo (capsule) against a dark background. * **Culture:** Niger seed agar/Bird seed agar (produces melanin). * **Antigen Detection:** CrAg (Cryptococcal Antigen) via Lateral Flow Assay is the most sensitive screening test. * **Histopathology:** Mucicarmine stain (stains capsule red). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: Which fungus is capable of forming a fungal ball?

Aspergillus. **Explanation:** **Aspergillus** is the most common cause of a **fungal ball (Aspergilloma)**. This occurs when the fungus colonizes a pre-existing lung cavity (most commonly formed by **Tuberculosis**, but also sarcoidosis or bronchiectasis). The fungus grows as a saprophytic mass of hyphae, fibrin, and cellular debris without invading the surrounding tissue. On a chest X-ray, it presents as a mobile, gravity-dependent mass with a characteristic **"Air-crescent sign" (Monod sign)**. **Analysis of Options:** * **Aspergillus (Correct):** Specifically *Aspergillus fumigatus*. It is unique in its ability to form non-invasive balls in pulmonary cavities. * **Mucor & Rhizopus (Incorrect):** These belong to the order Mucorales. They are characterized by **angioinvasion**, leading to infarction and necrosis (e.g., Rhinocerebral mucormycosis). They do not typically form organized, non-invasive fungal balls. * **Penicillium (Incorrect):** While *Talaromyces (Penicillium) marneffei* is a significant pathogen in HIV patients, it causes disseminated intracellular infection rather than cavitary fungal balls. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** Gold standard is culture; however, the presence of **serum precipitins (IgG antibodies)** against Aspergillus is highly sensitive for Aspergilloma. 2. **Microscopy:** Aspergillus shows **septate hyphae** with **acute-angle (45°) branching**, whereas Mucorales show broad, aseptate hyphae with right-angle branching. 3. **Clinical Presentation:** The most common symptom of an Aspergilloma is **hemoptysis**, which can occasionally be life-threatening. 4. **Treatment:** Surgical resection is the definitive treatment for symptomatic cases; systemic antifungals have poor penetration into the fungal ball.

Q: Systemic infection is caused by all fungi except?

Dermatophytes. **Explanation:** The classification of fungal infections is based on the depth of tissue involvement. Fungi are categorized into superficial, cutaneous, subcutaneous, and systemic (deep) mycoses. **Why Dermatophytes is the correct answer:** Dermatophytes (genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*) cause **cutaneous mycoses**. These fungi are "keratinophilic," meaning they require keratin for growth. Since keratin is only found in the non-living cornified layers of the skin, hair, and nails, these infections remain restricted to the **superficial integument**. They lack the biochemical machinery to invade deeper tissues or survive at core body temperatures, thus they **do not cause systemic infection.** **Analysis of Incorrect Options:** * **Cryptococcus:** An encapsulated yeast (primarily *C. neoformans*) that causes systemic disease, most notably meningitis and pulmonary infections, especially in immunocompromised patients. * **Histoplasma:** A dimorphic fungus that causes systemic histoplasmosis. It is an intracellular pathogen that involves the reticuloendothelial system (lungs, liver, spleen). * **Paracoccidioides:** A dimorphic fungus causing Paracoccidioidomycosis, a systemic infection prevalent in South America that affects the lungs and mucous membranes. **NEET-PG High-Yield Pearls:** * **Systemic Mycoses** are typically caused by dimorphic fungi (except *Cryptococcus*, which is a yeast). * **Dermatophytes** are diagnosed using KOH mounts showing branching hyphae and are treated with topical antifungals or oral Griseofulvin/Terbinafine. * **Wood’s Lamp:** Used to detect certain *Microsporum* species (fluoresce bright green). * **Culture Media:** Sabouraud Dextrose Agar (SDA) is the standard medium for most fungi.

Question 1

Candida infection is predisposed by all of the following, except:

Accepted Answer

Menstruation

Answer

Diabetes

Answer

Minipill users

Answer

Combined pill users

Question 2

Barrel-shaped arthroconidia are characteristic of which one of the following fungi?

Accepted Answer

C. immitis

Answer

E. floccosum

Answer

Phialophora verrucosa

Answer

M. canis

Question 3

Which of the following statements about Pneumocystis jiroveci is FALSE?

Accepted Answer

It is frequently associated with Cytomegalovirus (CMV).

Answer

It is typically seen only in immunocompromised individuals.

Answer

It may be associated with the development of a pneumatocele.

Answer

It is diagnosed using sputum microscopy.

Question 4

Which organism is known to be capsulated?

Accepted Answer

Cryptococcus neoformans

Answer

Histoplasma capsulatum

Answer

Neisseria gonorrhoeae

Answer

All the above

Question 5

Tinea Nigra is caused by which organism?

Accepted Answer

Hortaea werneckii

Answer

Piedrae hortae

Answer

T. rubrum

Answer

Microsporum

Question 6

A 56-year-old man undergoing chemotherapy for leukemia develops fever, nonproductive cough, dyspnea, pleuritic chest pain, and hemoptysis over one week. A chest CT scan shows multiple 1- to 4-cm nodular densities with surrounding ground-glass infiltrate (halo sign). Bronchoalveolar lavage fluid microscopy reveals narrow branching septate hyphae. His CBC shows Hgb, 13 g/dL; Hct, 38.7%; WBC count, 2000/mL; and platelet count, 200,100/mL. Which of the following organisms is the most likely cause of this infection?

Accepted Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Cryptococcus neoformans

Answer

Moraxella catarrhalis

Question 7

Impaired immune competence is the predisposing factor in about half of all persons who develop which of the following fungal infections?

Accepted Answer

Cryptococcosis

Answer

Histoplasmosis

Answer

Coccidoidomycosis

Answer

Blastomycosis

Question 8

Which fungus is capable of forming a fungal ball?

Accepted Answer

Aspergillus

Answer

Penicillium

Answer

Mucor

Answer

Rhizopus

Question 9

Systemic infection is caused by all fungi except?

Accepted Answer

Dermatophytes

Answer

Cryptococcus

Answer

Histoplasma

Answer

Paracoccidioides

Question 10

Giemsa stain of yeast cells in HIV is associated with which of the following infections?

Accepted Answer

Cryptococcosis

Answer

Aspergillosis

Answer

Blastomycosis

Answer

Histoplasmosis

Mycology — MCQs

Mycology — MCQs

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