Mycology Practice Questions

Q: Barrel-shaped spores are seen with which of the following fungi?

Coccidioides. **Explanation:** The correct answer is **Coccidioides** (Option C). **Why Coccidioides is correct:** *Coccidioides immitis* and *C. posadasii* are dimorphic fungi characterized by a unique life cycle. In the environment (soil) and in laboratory cultures (at 25°C), they form septate hyphae that fragment into highly infectious, thick-walled, **barrel-shaped arthroconidia** (arthrospores). These spores are typically separated by empty "disjunctor cells," giving them a characteristic "beaded" or "barrel" appearance under the microscope. In the human body (37°C), these spores transform into large **spherules** filled with endospores. **Why other options are incorrect:** * **Blastomyces:** Characterized by large, round-to-oval yeast cells with a **broad-based bud** and a thick, "doubly refractile" cell wall. * **Histoplasma:** Typically seen as small, intracellular yeast cells within macrophages. They do not form barrel-shaped spores; their diagnostic feature in culture is the **tuberculate macroconidia** (finger-like projections). * **Candida:** A yeast-like fungus that primarily reproduces by budding (blastoconidia) and forms **pseudohyphae**. In specific conditions (e.g., Cornmeal agar), *C. albicans* forms thick-walled **chlamydospores**. **High-Yield Clinical Pearls for NEET-PG:** * **Coccidioidomycosis** is also known as **Valley Fever** or Desert Rheumatism. * It is the **most virulent** of the systemic mycoses; laboratory cultures are a major biohazard. * **Morphology Shift:** Arthroconidia (Environment/Culture) → Spherules (Tissue). * **Geographic distribution:** Southwestern USA (Arizona, California), Mexico, and Central/South America. * **Clinical Triad:** Fever, joint pain (arthralgia), and erythema nodosum.

Q: A 40-year-old male presents with verrucous skin lesions. Microscopic examination of a tissue biopsy shows characteristic findings. What is the diagnosis?

Chromoblastomycosis. ***Chromoblastomycosis*** - **Verrucous skin lesions** are characteristic of chromoblastomycosis, caused by dematiaceous fungi like *Fonsecaea* and *Cladophialophora*. - Microscopic examination reveals pathognomonic **Medlar bodies** (sclerotic bodies/copper pennies) - thick-walled, brown, septate structures that are diagnostic. *Sporotrichosis* - Typically presents with **nodular lymphangitic** spread following trauma, not verrucous lesions. - Microscopy shows **cigar-shaped yeasts** of *Sporothrix schenckii*, not sclerotic bodies. *Rhinosporidiosis* - Characterized by **nasal polyps** and **friable masses** in mucous membranes, not skin verrucous lesions. - Microscopy reveals large **sporangia** containing **endospores** of *Rhinosporidium seeberi*, distinct from Medlar bodies. *Mycetoma* - Presents with **chronic granulomatous** swelling with **sinuses** and **grain discharge**, not verrucous appearance. - Microscopy shows **fungal grains** (white or black) depending on causative organism, not sclerotic bodies.

Q: A patient presents with foot swelling, pus discharge, and multiple sinuses. A KOH smear reveals filamentous structures. What is the most likely diagnosis?

Madura mycosis. ### Explanation The clinical presentation of **foot swelling, multiple discharging sinuses, and pus** is the classic triad of **Mycetoma** (Madura foot). **1. Why Madura Mycosis is correct:** Mycetoma can be caused by either fungi (**Eumycetoma/Madura mycosis**) or bacteria (**Actinomycetoma**). The key diagnostic clue here is the **KOH smear**, which reveals **filamentous structures** (fungal hyphae). In Madura mycosis, these hyphae are typically thick (2-4 μm) and septate. The presence of "grains" in the discharge is also a hallmark, representing colonies of the causative agent (e.g., *Madurella mycetomatis*). **2. Why other options are incorrect:** * **Actinomycosis:** While it also presents with sinuses and "sulfur granules," it typically involves the **cervicofacial region** (lumpy jaw). Under microscopy, *Actinomyces* are Gram-positive, branching, thin filamentous bacteria (not fungi), and are usually anaerobic. * **Osteomyelitis:** While chronic osteomyelitis can cause swelling and sinuses, it would not show filamentous structures on a KOH smear; it is typically caused by pyogenic bacteria like *Staphylococcus aureus*. * **Anthrax:** Cutaneous anthrax presents as a painless **black eschar** with surrounding edema, not chronic discharging sinuses. **3. High-Yield Clinical Pearls for NEET-PG:** * **Triad of Mycetoma:** Soft tissue swelling + Multiple discharging sinuses + Grains in pus. * **Eumycetoma (Fungal):** Caused by *Madurella mycetomatis* (Black grains). Shows thick hyphae on KOH. * **Actinomycetoma (Bacterial):** Caused by *Nocardia* or *Actinomadura*. Shows thin filaments (<1 μm) on Gram stain. * **Radiology:** The **"Dot-in-circle" sign** on MRI is pathognomonic for mycetoma.

Q: Orbital mucormycosis is a complication of -

Diabetic ketoacidosis. ### Explanation **Correct Answer: D. Diabetic ketoacidosis** **Why it is correct:** Orbital Mucormycosis (Rhino-oculo-cerebral mucormycosis) is a life-threatening opportunistic fungal infection caused by fungi of the order Mucorales (e.g., *Rhizopus oryzae*). **Diabetic Ketoacidosis (DKA)** is the most significant risk factor because: 1. **Acidosis:** The fungus possesses an enzyme called **ketone reductase**, which allows it to thrive in acidic, glucose-rich environments. 2. **Iron Availability:** Acidosis causes iron to dissociate from transferrin. Mucorales are "siderophilic" (iron-loving) and use this free iron for rapid growth and angioinvasion. **Why the other options are incorrect:** * **A. AIDS:** While AIDS causes many opportunistic infections (like Cryptococcosis or CMV), Mucormycosis is specifically linked to metabolic derangements (DKA) and neutropenia rather than isolated T-cell deficiency. * **B. Steroid therapy:** Long-term steroids increase the risk of fungal infections by causing hyperglycemia and immunosuppression, but DKA remains the classic, most high-yield association for the *orbital* presentation. * **C. Cushing's disease:** While it causes endogenous hypercortisolism and secondary diabetes, it rarely leads to the acute, severe ketoacidosis required for the rapid fulminant spread of Mucor. **Clinical Pearls for NEET-PG:** * **Hallmark Pathology:** Broad, **non-septate hyphae** with **right-angled (90°) branching**. * **Key Feature:** **Angioinvasion** leading to tissue infarction and the characteristic **black eschar** on the turbinates or palate. * **Clinical Presentation:** Sudden proptosis, internal/external ophthalmoplegia (due to involvement of orbital apex), and vision loss. * **Management:** Medical emergency requiring aggressive surgical debridement and intravenous **Liposomal Amphotericin B**. Control of the underlying DKA is the first step in management.

Q: Which of the following is NOT true about Cryptococcus?

Forms pseudohyphae. **Explanation:** The correct answer is **C (Forms pseudohyphae)**. *Cryptococcus neoformans* is a unique fungus because it is an **obligate yeast**. Unlike most other pathogenic yeasts (such as *Candida*), *Cryptococcus* does not produce pseudohyphae or true hyphae in clinical specimens or standard cultures. It exists solely as a round-to-oval budding yeast. **Analysis of Options:** * **A. Has a polysaccharide capsule:** This is a hallmark feature. *Cryptococcus* is the only medically important fungus with a prominent **glucuronoxylomannan capsule**, which is its primary virulence factor. It is visualized using **India Ink** (negative staining). * **B. Reproduces by budding:** As a yeast, it reproduces via narrow-based budding. * **D. Is urease positive:** *Cryptococcus* species characteristically produce the urease enzyme, which helps differentiate them from other yeasts like *Candida albicans* (which is urease negative). **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **India Ink** preparation shows a "halo" (capsule). The most sensitive screening test is the **CrAg (Cryptococcal Antigen)** lateral flow assay. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)**; produces creamy white colonies. On **Bird Seed Agar (Niger Seed Agar)**, it produces brown/black colonies due to phenoloxidase activity (melanin production). * **Clinical Presentation:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100). * **Histopathology:** Highlighted by **Mucicarmine stain** (stains the capsule bright red) and Masson-Fontana (stains melanin).

Q: An AIDS patient with clinical pneumonia has a bronchoalveolar lavage that demonstrates small, "hat-shaped" structures in alveoli that are about the size of an erythrocyte and stain with silver stains. The microorganism involved is most likely which of the following?

Pneumocystis jirovecii. ### Explanation **Correct Answer: D. Pneumocystis jirovecii** The clinical presentation and microscopic findings are classic for **Pneumocystis Pneumonia (PCP)**, an opportunistic infection caused by the fungus *Pneumocystis jirovecii*. * **Why it is correct:** In AIDS patients (typically CD4 < 200 cells/µL), *P. jirovecii* causes interstitial pneumonia. The diagnostic hallmark in bronchoalveolar lavage (BAL) or induced sputum is the presence of **cysts**. These cysts are roughly the size of an erythrocyte (5–8 µm), contain intracystic bodies, and are classically described as **"cup-shaped," "saucer-shaped," or "hat-shaped."** They do not grow on standard fungal media and require special stains like **Gomori Methenamine Silver (GMS)** or Toluidine blue to be visualized. **Analysis of Incorrect Options:** * **A. Aspergillus fumigatus:** Characterized by septate hyphae with acute-angle (45°) branching. It does not form small, hat-shaped cysts. * **B. Blastomyces dermatitidis:** A dimorphic fungus characterized by large, thick-walled yeast cells with **broad-based budding**. * **C. Mycobacterium avium:** An acid-fast bacillus (AFB) that causes systemic illness in advanced AIDS. It appears as slender rods on Ziehl-Neelsen stain, not as silver-staining cysts. **NEET-PG High-Yield Pearls:** * **Stain of choice:** GMS (silver stain) highlights the cyst wall; Giemsa stain highlights the trophic forms (nuclei). * **Radiology:** Characteristically shows bilateral, diffuse **"ground-glass opacities"** extending from the perihilar region. * **Biochemical Marker:** Elevated serum **Beta-D-Glucan** is often seen (non-specific but suggestive). * **Treatment:** First-line therapy and prophylaxis is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if $PaO_2 35$ mmHg.

Q: Prolonged use of antibiotics in children can result in which of the following conditions?

Candidiasis. **Explanation:** The correct answer is **B. Candidiasis**. **Mechanism of Action:** The human oral cavity and gastrointestinal tract maintain a delicate balance of normal microbial flora. Broad-spectrum or prolonged antibiotic therapy suppresses the growth of beneficial commensal bacteria (such as *Lactobacillus*). These bacteria normally compete with *Candida albicans* for nutrients and binding sites and maintain an acidic pH that inhibits fungal overgrowth. When this bacterial "interference" is removed, *Candida*—an opportunistic fungus—proliferates, leading to conditions like oral thrush or diaper dermatitis. **Analysis of Incorrect Options:** * **A. Necrotising Ulcerative Gingivitis (NUG):** Also known as "Trench Mouth," this is an acute infection caused by a fuso-spirochetal complex (e.g., *Prevotella intermedia*). It is associated with poor hygiene and immunosuppression, not antibiotic use. In fact, antibiotics are part of its treatment. * **C. Actinomycosis:** This is a chronic granulomatous infection caused by *Actinomyces israelii*. It typically occurs following local trauma (like dental extraction) and is treated with long-term penicillin; it is not caused by antibiotic use. * **D. Aphthous Ulcers:** These are painful, non-infectious oral ulcers. While their exact etiology is idiopathic, they are often linked to stress, trauma, or vitamin deficiencies (B12, Folate), rather than antibiotic-induced flora changes. **High-Yield Clinical Pearls for NEET-PG:** * **Oral Candidiasis (Thrush):** Characterized by white, "curd-like" plaques that **can be scraped off**, leaving an erythematous (bleeding) base. * **Other complications of prolonged antibiotics:** Pseudomembranous colitis (caused by *Clostridioides difficile* overgrowth) and Vitamin K deficiency (due to destruction of gut flora). * **Treatment:** Topical Nystatin or oral Fluconazole are the first-line agents for pediatric candidiasis.

Q: All of the following are dimorphic fungi except:

Cryptococcus. **Explanation:** The core concept tested here is the classification of fungi based on morphology. **Dimorphic fungi** are unique because they exist in two forms depending on environmental conditions (typically temperature): they are **molds** (filamentous) in the cold (25°C/soil) and **yeasts** in the heat (37°C/host tissue). **Why Cryptococcus is the correct answer:** **Cryptococcus neoformans** is a **monomorphic yeast**. Unlike dimorphic fungi, it remains a yeast both in nature (pigeon droppings) and in the human body (CSF/lungs). It is characterized by a thick polysaccharide capsule, which is its primary virulence factor and is visualized using India Ink. **Analysis of incorrect options (Dimorphic Fungi):** * **Blastomyces dermatitidis:** A dimorphic fungus found in soil. In tissue, it appears as characteristic "Broad-Based Budding" yeast. * **Histoplasma capsulatum:** A dimorphic fungus often associated with bird/bat guano. In tissue, it presents as small intracellular yeasts within macrophages. * **Paracoccidioides brasiliensis:** A dimorphic fungus prevalent in South America. In its yeast form, it shows multiple buds surrounding a central cell, resembling a "Pilot’s Wheel" or "Mickey Mouse" appearance. **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Dimorphic Fungi:** "**B**ody **H**eat **P**robably **C**hanges **S**hape" (**B**lastomyces, **H**istoplasma, **P**aracoccidioides, **C**occidioides, **S**porothrix, and *Talaromyces marneffei*). 2. **Coccidioides exception:** While dimorphic, it forms **spherules** containing endospores in tissue, not simple yeasts. 3. **Candida albicans:** Often called "pseudo-dimorphic" because it forms yeast at 25°C and germ tubes/hyphae at 37°C (the reverse of classic dimorphism).

Q: Which statement is false regarding Cryptococcus neoformans?

Urease negative. **Explanation:** *Cryptococcus neoformans* is an encapsulated opportunistic yeast that is a frequent subject of high-yield questions in NEET-PG. **1. Why Option C is the correct (False) statement:** *Cryptococcus neoformans* is characteristically **Urease positive**. It produces the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide. This property is a key laboratory diagnostic feature used to differentiate it from other yeasts like *Candida albicans* (which is urease negative). **2. Analysis of Incorrect Options (True statements):** * **Option A (Grows at 37°C):** Unlike many saprophytic fungi, *C. neoformans* can grow at 37°C (human body temperature), which is a vital virulence factor allowing it to cause systemic infection. * **Option B (Has 4 serotypes):** It is classified into four serotypes (**A, B, C, and D**) based on capsular polysaccharides. Serotypes A and D belong to *C. neoformans*, while B and C belong to *C. gattii*. * **Option D (Immunocompromised patients):** It is a classic opportunistic pathogen, most commonly causing meningitis in patients with HIV/AIDS (CD4 count <100 cells/µL) or those on prolonged immunosuppressants. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The most important virulence factor is the **Polysaccharide Capsule** (Glucuronoxylomannan). * **Microscopy:** Demonstrated by **India Ink** preparation (shows a clear halo against a dark background) or **Nigrosin**. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as mucoid colonies. On **Niger Seed Agar (Birdseed Agar)**, it produces brown/black colonies due to phenoloxidase activity (melanin production). * **Antigen Detection:** Lateral Flow Assay (LFA) for cryptococcal antigen is the most sensitive rapid diagnostic test.

Q: Which of the following fungi is difficult to isolate on regular Sabouraud Dextrose Agar (SDA) media?

Malassezia furfur. **Explanation:** The correct answer is **Malassezia furfur**. **1. Why Malassezia furfur is the correct answer:** *Malassezia furfur* is a **lipophilic (fat-loving) fungus** that is part of the normal skin flora. Unlike most other fungi, it lacks the ability to synthesize long-chain fatty acids. Therefore, it cannot grow on standard Sabouraud Dextrose Agar (SDA) because the medium lacks the necessary lipids. To isolate it in a laboratory setting, the media must be supplemented with **olive oil** or other long-chain fatty acids (e.g., Dixon’s agar). **2. Why the other options are incorrect:** * **Candida:** These are opportunistic yeasts that grow rapidly (within 24–48 hours) on standard SDA, forming smooth, cream-colored colonies. * **Dermatophytes:** (e.g., *Trichophyton*, *Microsporum*) These fungi utilize keratin and grow well on SDA, though specialized media like Dermatophyte Test Medium (DTM) are often used for better visualization of pigment and morphology. * **Cryptococcus:** *Cryptococcus neoformans* grows well on SDA as mucoid colonies. While specialized media like Niger Seed Agar (Birdseed Agar) are used to demonstrate melanin production, SDA is sufficient for primary isolation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** On KOH mount, *M. furfur* shows a characteristic **"Spaghetti and Meatballs"** appearance (short curved hyphae and thick-walled yeast cells). * **Clinical Condition:** It causes **Pityriasis (Tinea) versicolor**, characterized by hypo- or hyperpigmented macules. * **Wood’s Lamp:** Lesions show a characteristic **golden-yellow fluorescence**. * **Systemic Association:** It can cause catheter-associated fungemia in neonates receiving parenteral lipid emulsions.

Question 1

Barrel-shaped spores are seen with which of the following fungi?

Accepted Answer

Coccidioides

Answer

Blastomyces

Answer

Histoplasma

Answer

Candida

Question 2

A 40-year-old male presents with verrucous skin lesions. Microscopic examination of a tissue biopsy shows characteristic findings. What is the diagnosis?

Accepted Answer

Chromoblastomycosis

Answer

Sporotrichosis

Answer

Rhinosporidiosis

Answer

Mycetoma

Question 3

A patient presents with foot swelling, pus discharge, and multiple sinuses. A KOH smear reveals filamentous structures. What is the most likely diagnosis?

Accepted Answer

Madura mycosis

Answer

Osteomyelitis

Answer

Anthrax

Answer

Actinomycosis

Question 4

Orbital mucormycosis is a complication of -

Accepted Answer

Diabetic ketoacidosis

Answer

AIDS

Answer

Steroid therapy

Answer

Cushing's disease

Question 5

Which of the following is NOT true about Cryptococcus?

Accepted Answer

Forms pseudohyphae

Answer

Has a polysaccharide capsule

Answer

Reproduces by budding

Answer

Is urease positive

Question 6

An AIDS patient with clinical pneumonia has a bronchoalveolar lavage that demonstrates small, "hat-shaped" structures in alveoli that are about the size of an erythrocyte and stain with silver stains. The microorganism involved is most likely which of the following?

Accepted Answer

Pneumocystis jirovecii

Answer

Aspergillus fumigatus

Answer

Blastomyces dermatitidis

Answer

Mycobacterium avium

Question 7

Prolonged use of antibiotics in children can result in which of the following conditions?

Accepted Answer

Candidiasis

Answer

Necrotising ulcerative gingivitis

Answer

Actinomycosis

Answer

Aphthous ulcers

Question 8

All of the following are dimorphic fungi except:

Accepted Answer

Cryptococcus

Answer

Blastomycoses

Answer

Histoplasma

Answer

Paracoccidia

Question 9

Which statement is false regarding Cryptococcus neoformans?

Accepted Answer

Urease negative

Answer

Grows at 37°C

Answer

Has 4 serotypes

Answer

Causes infection in immunocompromised patients

Question 10

Which of the following fungi is difficult to isolate on regular Sabouraud Dextrose Agar (SDA) media?

Accepted Answer

Malassezia furfur

Answer

Candida

Answer

Dermatophytes

Answer

Cryptococcus

Mycology — MCQs

Mycology — MCQs

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