Mycology Practice Questions

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.

Q: Denture sore mouth is caused by which of the following microorganisms?

Candida albicans. **Explanation:** **Denture Sore Mouth**, also known as **Chronic Atrophic Candidiasis**, is a common form of oral candidiasis. It is primarily caused by an overgrowth of **Candida albicans** (Option B). The condition typically occurs under ill-fitting or poorly cleaned dentures. The space between the denture base and the palatal mucosa creates a warm, moist, and anaerobic environment with low pH, which promotes the proliferation of Candida. Clinically, it presents as diffuse erythema and edema of the mucosa covered by the denture, often without the typical white "curd-like" patches seen in pseudomembranous candidiasis. **Analysis of Incorrect Options:** * **Option A (Actinomyces):** These are Gram-positive anaerobic bacteria responsible for Actinomycosis ("Lumpy Jaw"). They cause chronic granulomatous lesions with sulfur granules, not generalized mucosal soreness under dentures. * **Option C (Blastomyces):** This is a systemic fungal infection (Blastomycosis) that primarily affects the lungs. While it can have oral manifestations, they usually present as chronic non-healing ulcers or verrucous lesions, not as denture-related stomatitis. **Clinical Pearls for NEET-PG:** * **Newton’s Classification:** Used to grade Denture Stomatitis (Type I: Localized inflammation; Type II: Diffuse erythema; Type III: Papillary hyperplasia). * **Predisposing Factors:** Poor oral hygiene, continuous denture wear (not removing them at night), and xerostomia. * **Management:** Improving denture hygiene, soaking dentures in antifungal solutions (e.g., Nystatin), and ensuring a proper fit. * **Key Association:** Often associated with **Angular Cheilitis** (Perleche), which is also frequently caused by *C. albicans*.

Q: The granules discharged in mycetoma contain which of the following?

Fungal colonies. **Explanation:** The hallmark of **Mycetoma** (Madura foot) is the triad of localized swelling, multiple interconnecting sinus tracts, and the discharge of **granules**. These granules are not merely debris; they are organized, compact **micro-colonies of the causative agent** (either fungi in eumycetoma or filamentous bacteria in actinomycetoma) embedded in a matrix. * **Why Option B is correct:** In eumycetoma, the granules represent dense aggregates of fungal hyphae. The color, size, and consistency of these granules provide a diagnostic clue to the specific species (e.g., black granules in *Madurella mycetomatis*). * **Why Options C and D are incorrect:** While pus cells (neutrophils) and inflammatory cells (lymphocytes, plasma cells, and giant cells) are present in the surrounding tissue and the discharge as part of the host's immune response, they do not constitute the "granule" itself. The granule is the pathogen's structural form within the lesion. * **Why Option A is incorrect:** Although chronic mycetoma can lead to underlying bone destruction (osteomyelitis) with a "moth-eaten" appearance on X-ray, bone spicules are not typically discharged in the sinus fluid. **High-Yield Clinical Pearls for NEET-PG:** 1. **Eumycetoma:** Caused by fungi; granules are usually large and can be black or white. 2. **Actinomycetoma:** Caused by aerobic actinomycetes (e.g., *Nocardia*, *Actinomadura*); granules are usually smaller and white, yellow, or red. 3. **Diagnosis:** Direct microscopy of the granule (KOH mount) reveals the morphology of the agent. 4. **GMS/PAS Stains:** Best for visualizing fungal hyphae within the granules.

Q: All of the following are true about mucormycosis, except:

Long-term deferoxamine therapy. **Explanation:** Mucormycosis is a life-threatening opportunistic infection caused by fungi of the order Mucorales (e.g., *Rhizopus*, *Mucor*). **Why Option D is the correct answer (The "Except"):** Mucorales are characterized by **broad, ribbon-like, aseptate (or sparsely septate)** hyphae that branch at **right angles (90°)**. In contrast, septate hyphae with acute-angle branching (45°) are characteristic of *Aspergillus*. **Analysis of other options:** * **Angioinvasion (Option B):** This is a hallmark of Mucormycosis. The fungi invade blood vessel walls, leading to thrombosis, tissue ischemia, and the characteristic black necrotic eschar. * **Long-term Deferoxamine Therapy (Option C):** This is a known risk factor. *Rhizopus* uses deferoxamine as a **siderophore** to scavenge iron for its growth. (Note: Newer iron chelators like Deferasirox do not increase this risk). * **Lymphatic Invasion (Option A):** While angioinvasion is more prominent, the fungus can spread via lymphatics and direct tissue extension. **NEET-PG High-Yield Pearls:** 1. **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Ketoacidosis** due to increased free iron), neutropenia, and corticosteroid use. 2. **Diagnosis:** KOH mount or biopsy showing broad, non-septate hyphae. 3. **Clinical Form:** Rhinocerebral mucormycosis is the most common presentation. 4. **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). Isavuconazole and Posaconazole are alternatives.

Question 1

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 2

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 3

Pneumocystis jirovecii is a:

Accepted Answer

Fungus

Answer

Protozoan

Answer

Gram-negative bacterium

Answer

None of the above

Question 4

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 5

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 6

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

Accepted Answer

Candida

Answer

Trichomonas

Answer

Mobiluncus

Answer

Chlamydia

Question 7

Black dot ringworm is caused by which of the following?

Accepted Answer

Trichophyton

Answer

Microsporum

Answer

Epidermophyton

Answer

Candida

Question 8

Denture sore mouth is caused by which of the following microorganisms?

Accepted Answer

Candida albicans

Answer

Actinomyces

Answer

Blastomyces

Answer

None of the above

Question 9

The granules discharged in mycetoma contain which of the following?

Accepted Answer

Fungal colonies

Answer

Bone spicules

Answer

Pus cells

Answer

Inflammatory cells

Question 10

All of the following are true about mucormycosis, except:

Accepted Answer

Long-term deferoxamine therapy

Answer

Lymphatic invasion

Answer

Angioinvasion

Answer

Septate hyphae

Mycology — MCQs

Mycology — MCQs

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