Mycology Practice Questions

Q: A 28-year-old HIV patient presents with non-productive cough and progressively increasing difficulty in breathing. Chest X-ray shows diffuse bilateral interstitial infiltrates along with pneumatocele. Gomori's methenamine silver staining of the bronchoalveolar lavage shows a characteristic oval yeast. The most probable causative organism is?

Pneumocystis jirovecii. ### Explanation **Correct Option: B. Pneumocystis jirovecii** The clinical presentation is classic for **Pneumocystis Pneumonia (PCP)**, an opportunistic infection typically seen in HIV patients with CD4 counts <200 cells/mm³. * **Clinical Features:** Patients present with a triad of dyspnea, non-productive cough, and fever. * **Radiology:** Chest X-ray characteristically shows **diffuse bilateral perihilar interstitial infiltrates** (ground-glass opacities). The presence of **pneumatoceles** (thin-walled air-filled cysts) is a high-yield radiological marker for PCP. * **Microscopy:** *P. jirovecii* cannot be cultured. Diagnosis relies on staining (BAL or induced sputum). **Gomori’s Methenamine Silver (GMS)** stain highlights the characteristic **crushed-ping-pong ball** or oval-shaped cysts (yeast-like forms) with central dark spots. --- ### Why Other Options are Incorrect: * **A. Histoplasma capsulatum:** While it causes pulmonary symptoms in HIV, it typically presents with miliary nodules or hilar lymphadenopathy. On staining, it appears as small intracellular yeasts within macrophages, not as extracellular cysts in BAL. * **C. Rhinosporidium seeberi:** This causes rhinosporidiosis, characterized by friable, leafy nasal polyps. It is not a respiratory pathogen and is identified by large sporangia containing endospores. * **D. Cryptococcus neoformans:** Usually presents as meningitis in HIV. Pulmonary involvement shows well-defined nodules or consolidation. It is best identified by India Ink (capsule) or Mucicarmine stain. --- ### NEET-PG High-Yield Pearls: * **Drug of Choice:** Trimethoprim-Sulfamethoxazole (Cotrimoxazole). * **Prophylaxis:** Started in HIV patients when CD4 count falls below **200 cells/mm³**. * **Stains:** GMS (best for cysts), Giemsa (highlights trophic forms), and Toluidine blue O. * **Biomarker:** Elevated **Serum Beta-D-Glucan** is a sensitive but non-specific marker for PCP.

Q: Mature spherules in a sputum sample are seen in which of the following fungal infections?

Coccidioidomycosis. ### Explanation **Correct Answer: C. Coccidioidomycosis** **Why it is correct:** *Coccidioides immitis* and *C. posadasii* are dimorphic fungi characterized by a unique life cycle. In the environment (soil), they exist as hyphae with infectious **arthroconidia**. Once inhaled into the lungs, these arthroconidia transform into **spherules** (20–100 µm in diameter). As the spherule matures, its contents undergo progressive cleavage to form hundreds of **endospores**. The presence of these thick-walled, endospore-containing spherules in sputum, biopsy, or KOH mounts is pathognomonic for Coccidioidomycosis. **Why the other options are incorrect:** * **Options A & B (Staphylococcus and Streptococcus):** These are Gram-positive bacteria, not fungi. They appear as cocci in clusters or chains, respectively, and do not form spherules. * **Option D (Aspergillus):** This is an opportunistic filamentous fungus. In clinical samples, it typically presents as **septate hyphae** with acute-angle (45°) branching. It does not form spherules. **High-Yield Clinical Pearls for NEET-PG:** * **Geographic Niche:** Often called "Valley Fever" or "Desert Rheumatism"; endemic to the Southwestern USA (Arizona, California) and Central/South America. * **Morphology:** Remember the phrase **"Spherules with endospores"** for tissue/sputum samples. * **Culture Warning:** Arthroconidia are highly infectious; laboratory personnel must handle cultures with extreme caution (Biosafety Level 3). * **Clinical Triad:** Fever, joint pain (arthralgia), and erythema nodosum (Desert Rheumatism). * **Diagnosis:** Silver stains (GMS) or PAS stains are excellent for visualizing the spherule wall.

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

Mucormycosis. **Explanation:** The clinical presentation and microscopic findings are classic for **Mucormycosis**, a life-threatening opportunistic fungal infection. **Why Mucormycosis is correct:** 1. **Clinical Context:** Diabetes mellitus (especially with ketoacidosis) is the most significant risk factor. The "pus from the eye" suggests **Rhinocerebral Mucormycosis**, where the fungus spreads from the sinuses to the orbit. 2. **Microscopic Features:** The hallmark of Mucorales (e.g., *Rhizopus*, *Mucor*) is **broad, non-septate (coenocytic) hyphae** with **obtuse-angled (90°) branching**. 3. **Gross Morphology:** These fungi grow rapidly as "lid-lifters" with a cottony appearance that turns **black/grey** due to sporangia formation. **Why other options are incorrect:** * **Aspergillosis:** Characterized by **septate hyphae** with **acute-angled (45°) branching**. While it can cause orbital cellulitis, the branching pattern is the key differentiator. * **Candidiasis:** Typically presents as budding yeast cells and **pseudohyphae**. It does not produce non-septate hyphae or black colonies in this context. * **Histoplasmosis:** A dimorphic fungus that appears as small, intracellular yeast cells within macrophages. It is primarily a systemic/pulmonary infection. **High-Yield NEET-PG Pearls:** * **Angioinvasion:** Mucorales have a predilection for invading blood vessels, leading to thrombosis and tissue necrosis (black eschar). * **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). * **Culture:** Sabouraud Dextrose Agar (SDA) shows rapid growth (2–3 days). * **Stains:** Best visualized with KOH mount, PAS, or GMS stains.

Q: A vitreous aspirate from a case of metastatic endophthalmitis on culture yields Gram-positive round to oval cells, 12-14 µm in size. The aspirate on Gram staining shows the presence of pseudohyphae. Which of the following is the most likely aetiological agent?

Candida. **Explanation:** The correct answer is **Candida**. The diagnosis is based on the morphological description provided in the clinical scenario. **1. Why Candida is correct:** * **Morphology:** *Candida* species are characterized by **Gram-positive, oval budding yeast cells** (4–6 µm, though they can appear larger in clinical samples) and the formation of **pseudohyphae**. Pseudohyphae are chains of elongated blastoconidia that remain attached, showing distinct constrictions at the septations (unlike true hyphae). * **Clinical Context:** **Metastatic endophthalmitis** (endogenous endophthalmitis) typically occurs via hematogenous spread. *Candida albicans* is the most common fungal cause of endogenous endophthalmitis, especially in immunocompromised patients, IV drug users, or those with long-term indwelling catheters. **2. Why other options are incorrect:** * **Aspergillus:** These are filamentous fungi characterized by **septate hyphae** that branch at **acute angles (45°)**. They do not produce yeast cells or pseudohyphae. * **Rhizopus:** These belong to Mucormycetes and show **broad, ribbon-like, non-septate (coenocytic) hyphae** with wide-angle branching (90°). * **Fusarium:** While a common cause of keratitis, it presents as septate hyphae and produces characteristic sickle-shaped macroconidia. It does not form budding yeast cells. **High-Yield NEET-PG Pearls:** * **Germ Tube Test (Reynolds-Braude Phenomenon):** The specific gold standard for identifying *C. albicans*. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white, smooth colonies with a "yeasty" odor. * **Chlamydospores:** *C. albicans* produces thick-walled terminal chlamydospores on Cornmeal Agar. * **Drug of Choice:** For *Candida* endophthalmitis, systemic Fluconazole or Voriconazole is used, often with intravitreal Amphotericin B.

Q: Aspergillosis can present with which of the following manifestations, except?

Rhinocerebral involvement. **Explanation:** The correct answer is **D. Rhinocerebral involvement**. This is because rhinocerebral infection is the classic hallmark of **Mucormycosis** (caused by *Rhizopus* or *Mucor*), particularly in patients with diabetic ketoacidosis or severe neutropenia. While *Aspergillus* can cause sinusitis, the aggressive, angioinvasive rhinocerebral syndrome involving the palate, orbit, and brain is characteristic of the Zygomycetes family, not *Aspergillus*. **Analysis of other options:** * **A. Lung cavity:** *Aspergillus* commonly colonizes pre-existing lung cavities (e.g., from old TB) to form an **Aspergilloma** (fungus ball). It can also cause cavitary lesions in Chronic Pulmonary Aspergillosis (CPA). * **B. Ear infection:** *Aspergillus niger* is the most common cause of **Otomycosis** (fungal otitis externa), typically presenting with black spores and itching. * **C. Normal component in sputum:** *Aspergillus* spores are ubiquitous in the environment. Finding them in a sputum sample does not necessarily indicate disease; it often represents transient inhalation or laboratory contamination, making it a "normal" or non-pathogenic finding in healthy individuals. **High-Yield Clinical Pearls for NEET-PG:** * **Aspergilloma:** Shows the **"Monod Sign"** or **"Air Crescent Sign"** on X-ray/CT (air surrounding the fungus ball). * **ABPA (Allergic Bronchopulmonary Aspergillosis):** Associated with asthma, central bronchiectasis, and high IgE levels. * **Morphology:** *Aspergillus* shows **septate hyphae** with **acute-angle (45°) branching**, whereas *Mucor* shows non-septate hyphae with right-angle (90°) branching. * **Drug of Choice:** Voriconazole is the gold standard for Invasive Aspergillosis.

Q: Pneumocystis jirovecii is a:

Fungus. **Explanation:** *Pneumocystis jirovecii* was historically classified as a protozoan due to its morphological features (cysts and trophozoites) and its lack of response to traditional antifungal drugs like Amphotericin B. However, modern molecular techniques, specifically **rRNA sequence analysis**, have definitively reclassified it as a **fungus**. **Why the correct answer is right:** * **Genetic Evidence:** DNA analysis shows it is closely related to Ascomycetous fungi. * **Cell Wall Composition:** Its cell wall contains **beta-1,3-glucan**, a characteristic fungal component (though it notably lacks ergosterol, which explains its resistance to many antifungals). **Why incorrect options are wrong:** * **B. Protozoan:** This was the old classification based on its life cycle stages. Unlike protozoa, *P. jirovecii* cannot be cultured in standard media and lacks certain protozoal organelles. * **C. Gram-negative bacterium:** It does not possess a bacterial cell wall or prokaryotic internal structures. While it is treated with Trimethoprim-Sulfamethoxazole (an antibacterial), this is due to its specific metabolic pathways, not its classification. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** It cannot be seen on Gram stain. The gold standard is **Gomori Methenamine Silver (GMS)** stain, which shows "crushed ping-pong ball" shaped cysts. * **Clinical Presentation:** It causes **Pneumocystis Pneumonia (PCP)**, an opportunistic infection in HIV patients (CD4 count <200 cells/µL). * **Radiology:** Characterized by bilateral, perihilar "ground-glass" opacities. * **Treatment of Choice:** High-dose **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if $PaO_2 < 70$ mmHg.

Q: A 40-year-old man presents with an ulcerative lesion on his right thumb, sustained while gardening. Culture reveals moist, creamy colonies. What is the most common causative organism?

Sporothrix. ### Explanation **Correct Answer: D. Sporothrix** **Reasoning:** The clinical presentation describes a classic case of **Sporotrichosis** (Rose Gardener’s disease). The key diagnostic clues are the **traumatic inoculation** (gardening injury) and the **dimorphic nature** of the fungus. *Sporothrix schenckii* is a thermally dimorphic fungus. In the environment (or at 25°C), it grows as a mold with septate hyphae and "rosette-like" conidia. However, in the body (or at 37°C on enriched media), it converts into a **yeast phase**, which appears as **moist, creamy, white-to-beige colonies** on culture. **Analysis of Incorrect Options:** * **A. Blastomyces:** While also dimorphic, *Blastomyces dermatitidis* typically presents with pulmonary symptoms or systemic dissemination. It is endemic to North America (Ohio/Mississippi River valleys) and is not specifically associated with gardening-related thumb ulcers in the Indian context. * **B. Phaeohyphomycosis:** This refers to infections caused by pigmented (dematiaceous) fungi. These would typically produce dark brown or black colonies due to melanin production, not "creamy" colonies. * **C. Rhinosporidium:** *Rhinosporidium seeberi* causes friable, strawberry-like nasal polyps. Crucially, it **cannot be cultured** on artificial media; diagnosis relies on identifying sporangia in histopathology. **NEET-PG High-Yield Pearls:** * **Clinical Pattern:** Often follows a **lymphocutaneous distribution** (nodules/ulcers ascending along lymphatic channels). * **Morphology:** In tissue, it shows **"Cigar-shaped" bodies**. * **Asteroid Bodies:** Represent the Splendore-Hoeppli phenomenon (eosinophilic material surrounding the yeast). * **Drug of Choice:** **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. * **Culture:** At 25°C, colonies turn from creamy to **dark brown/black** over time (leathery appearance).

Q: A 13-year-old girl presents with non-healing leg ulcers. Which of the following is likely to be the causative agent?

Sporothrix. The correct answer is **A. Sporothrix**. ### **Explanation** The clinical presentation of non-healing ulcers, particularly in a young patient, points toward **Sporotrichosis** (Rose Gardener’s disease), caused by the dimorphic fungus *Sporothrix schenckii*. 1. **Mechanism:** Infection typically occurs via **traumatic inoculation** of soil, moss, or decaying vegetation into the skin. 2. **Clinical Presentation:** It begins as a painless papule at the site of inoculation (often the hand or leg), which eventually ulcerates. A classic high-yield feature is **lymphocutaneous spread**, where secondary nodules and ulcers develop along the lines of lymphatic drainage. ### **Analysis of Incorrect Options** * **B. Cladophora:** This is a genus of green algae, not a primary human pathogen. It is not associated with cutaneous ulcerations. * **C. Aspergillus:** While *Aspergillus* can cause cutaneous infections (Primary Cutaneous Aspergillosis), it typically occurs in severely immunocompromised patients (e.g., neutropenic) and presents as necrotic black eschars rather than simple chronic ulcers in a healthy 13-year-old. * **D. Bacteroides:** These are anaerobic bacteria primarily involved in intra-abdominal infections or abscesses. While they can be part of polymicrobial skin infections (like necrotizing fasciitis), they are not a classic cause of isolated, non-healing leg ulcers in this demographic. ### **NEET-PG High-Yield Pearls** * **Asteroid Bodies:** Histology may show a central fungal spore surrounded by eosinophilic radiating projections (Splendore-Hoeppli phenomenon). * **Culture:** At 25°C, it shows a "flower-like" or **rosette arrangement** of conidia. * **Drug of Choice:** **Itraconazole** is the gold standard. Historically, Saturated Solution of Potassium Iodide (SSKI) was used. * **Differential Diagnosis:** Always consider *Mycobacterium marinum* (Fish tank granuloma) if a similar lymphatic pattern is described.

Q: Smear of vaginal discharge shows budding yeast cells. What is the causative agent?

Candida. **Explanation:** The presence of **budding yeast cells** (with or without pseudohyphae) in a vaginal discharge smear is the classic microbiological hallmark of **Vulvovaginal Candidiasis (VVC)**. 1. **Why Candida is correct:** *Candida albicans* is a dimorphic fungus that exists as oval, Gram-positive budding yeast cells (blastospores). In a wet mount or Gram stain of vaginal discharge, these yeast cells are diagnostic. Clinically, this presents as a thick, white, "curd-like" or "cottage cheese" discharge with significant pruritus and a normal vaginal pH (<4.5). 2. **Why the other options are incorrect:** * **Trichomonas vaginalis:** A flagellated protozoan. Diagnosis is made by observing **motile, pear-shaped trophozoites** on a wet mount. It causes a greenish-yellow, frothy discharge. * **Mobiluncus:** An anaerobic, Gram-variable, curved rod associated with **Bacterial Vaginosis (BV)**. BV is characterized by "Clue cells" (epithelial cells covered in bacteria) and a fishy odor (positive Whiff test), not yeast cells. * **Chlamydia trachomatis:** An obligate intracellular bacterium. It cannot be seen on a standard light microscope smear and typically causes mucopurulent cervicitis rather than primary vaginitis. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** The specific gold standard for identifying *C. albicans*. * **Culture:** Sabouraud Dextrose Agar (SDA) is the standard medium; colonies appear creamy white with a "yeasty" odor. * **Risk Factors:** Diabetes mellitus, pregnancy, and prolonged antibiotic use are common triggers for VVC. * **Treatment:** Topical clotrimazole or a single dose of oral Fluconazole (150 mg).

Q: Black dot ringworm is caused by which of the following?

Trichophyton. **Explanation:** **Black dot ringworm** is a clinical presentation of **Tinea capitis** characterized by small, black, soot-like dots on the scalp. This occurs due to **endothrix infection**, where the fungus grows inside the hair shaft, making it brittle. The hair breaks off flush at the scalp surface, leaving the distal portion of the hair follicle plugged with debris and fungal spores. 1. **Why Trichophyton is correct:** The most common causes of black dot Tinea capitis are **Trichophyton tonsurans** and **Trichophyton violaceum**. These species are "endothrix" (infecting the inside of the hair shaft). Because the hair shaft is weakened internally, it snaps at the skin line, creating the "black dot" appearance. 2. **Why other options are incorrect:** * **Microsporum:** Generally causes **ectothrix** infections (spores on the outside of the hair shaft). This typically results in "Grey patch" Tinea capitis, where the hair breaks further away from the scalp, and the area appears scaly and dull. * **Epidermophyton:** This genus primarily affects the skin (Tinea cruris/pedis) and nails. Crucially, **Epidermophyton does not infect hair.** * **Candida:** While it causes various mucocutaneous infections (like oral thrush or intertrigo), it is not a dermatophyte and does not cause the specific clinical pattern of ringworm or black dot alopecia. **High-Yield Clinical Pearls for NEET-PG:** * **Endothrix (Black Dot):** *T. tonsurans* (most common worldwide), *T. violaceum*. These do **not** fluoresce under Wood’s lamp. * **Ectothrix (Grey Patch):** *Microsporum audouinii*, *M. canis*. These **do** fluoresce (bright green) under Wood’s lamp. * **Favus:** Caused by *T. schoenleinii*; characterized by **scutula** (crusts) and permanent scarring alopecia. * **Drug of Choice:** Oral **Griseofulvin** remains the gold standard for Tinea capitis, though Terbinafine is also frequently used.

Question 1

A 28-year-old HIV patient presents with non-productive cough and progressively increasing difficulty in breathing. Chest X-ray shows diffuse bilateral interstitial infiltrates along with pneumatocele. Gomori's methenamine silver staining of the bronchoalveolar lavage shows a characteristic oval yeast. The most probable causative organism is?

Accepted Answer

Pneumocystis jirovecii

Answer

Histoplasma capsulatum

Answer

Rhinosporidium seeberi

Answer

Cryptococcus neoformans

Question 2

Mature spherules in a sputum sample are seen in which of the following fungal infections?

Accepted Answer

Coccidioidomycosis

Answer

Staphylococcus

Answer

Streptococcus

Answer

Aspergillus

Question 3

A diabetic patient presents with pus from the eye. Colonies of isolated organisms 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 4

A vitreous aspirate from a case of metastatic endophthalmitis on culture yields Gram-positive round to oval cells, 12-14 µm in size. The aspirate on Gram staining shows the presence of pseudohyphae. Which of the following is the most likely aetiological agent?

Accepted Answer

Candida

Answer

Aspergillus

Answer

Rhizopus

Answer

Fusarium

Question 5

Aspergillosis can present with which of the following manifestations, except?

Accepted Answer

Rhinocerebral involvement

Answer

Lung cavity

Answer

Ear infection

Answer

Normal component in sputum

Question 6

Pneumocystis jirovecii is a:

Accepted Answer

Fungus

Answer

Protozoan

Answer

Gram-negative bacterium

Answer

None of the above

Question 7

A 40-year-old man presents with an ulcerative lesion on his right thumb, sustained while gardening. Culture reveals moist, creamy colonies. What is the most common causative organism?

Accepted Answer

Sporothrix

Answer

Blastomyces

Answer

Phaeohyphomycosis

Answer

Rhinosporidium

Question 8

A 13-year-old girl presents with non-healing leg ulcers. Which of the following is likely to be the causative agent?

Accepted Answer

Sporothrix

Answer

Cladophora

Answer

Aspergillus

Answer

Bacteroides

Question 9

Smear of vaginal discharge shows budding yeast cells. What is the causative agent?

Accepted Answer

Candida

Answer

Trichomonas

Answer

Mobiluncus

Answer

Chlamydia

Question 10

Black dot ringworm is caused by which of the following?

Accepted Answer

Trichophyton

Answer

Microsporum

Answer

Epidermophyton

Answer

Candida

Mycology — MCQs

Mycology — MCQs

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