Mycology — MCQs

A gardener presents with a subcutaneous lesion on the hand, which he thinks resulted from a wound he received while he was making a sphagnum moss-wire frame for a floral wreath. The nodule has ulcerated and not healed despite use of antibacterial cream, and a new nodule is forming above the original lesion. What is the most likely appropriate treatment for this infection?

Q230Easy

The germ tube test is diagnostic for which of the following organisms?

Mycology Indian Medical PG Practice Questions and MCQs

Question 221: Which of the following best describes fungi?

A. Prokaryotes
B. Eukaryotes (Correct Answer)
C. Plants
D. Animals

Explanation: **Explanation:** Fungi are classified as **Eukaryotes** because they possess a well-defined, membrane-bound nucleus and complex membrane-bound organelles (such as mitochondria and endoplasmic reticulum). Unlike bacteria, their DNA is organized into multiple linear chromosomes associated with histone proteins. **Analysis of Options:** * **A. Prokaryotes:** This category includes Bacteria and Archaea. Prokaryotes lack a nuclear membrane and membrane-bound organelles. Their cell walls are typically made of peptidoglycan, whereas fungal cell walls are composed of **chitin, glucans, and mannan.** * **C. Plants:** While fungi were once classified with plants due to their immobility and cell walls, they are distinct because they are **heterotrophic** (cannot perform photosynthesis) and lack chlorophyll. * **D. Animals:** Although fungi are more closely related to animals than plants (both are heterotrophs), animals lack cell walls and ingest food, whereas fungi absorb nutrients after extracellular digestion. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cell Membrane:** Fungal cell membranes contain **Ergosterol** instead of cholesterol. This is the primary target for antifungal drugs like Amphotericin B (binds ergosterol) and Azoles (inhibit ergosterol synthesis). 2. **Cell Wall:** The presence of **Chitin** (a polymer of N-acetylglucosamine) provides structural rigidity. Echinocandins (e.g., Caspofungin) target the synthesis of **1,3-beta-D-glucan** in the cell wall. 3. **Reproduction:** Fungi can reproduce both sexually (teleomorph) and asexually (anamorph). 4. **Thermal Dimorphism:** A key feature of systemic pathogens (e.g., *Histoplasma*); they exist as **molds** at 25°C (environment) and **yeasts** at 37°C (body).

Question 222: Which of the following is NOT true about Cryptococcus?

A. Has a polysaccharide capsule
B. Reproduces by budding
C. Forms pseudohyphae (Correct Answer)
D. Is urease positive

Explanation: **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).

Question 223: 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?

A. Aspergillus fumigatus
B. Blastomyces dermatitidis
C. Mycobacterium avium
D. Pneumocystis jirovecii (Correct Answer)

Explanation: ### 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 $PaO_2 < 70$ mmHg or A-a gradient $> 35$ mmHg.

Question 224: In an AIDS patient with a CD4 count between 100 and 50 cells/mm3, who presents with headache, neck stiffness, and disorientation, fungal meningitis is suspected. Which of the following is the purpose of ordering serology tests for common fungal etiologies of meningitis?

A. Detection of antibody to capsular polysaccharide
B. Detection of antibody to cell wall mannoprotein
C. Detection of capsular polysaccharide (Correct Answer)
D. Detection of cell wall mannoprotein

Explanation: **Explanation:** The clinical presentation of headache, neck stiffness, and disorientation in an AIDS patient with a low CD4 count (<100 cells/mm³) strongly suggests **Cryptococcal meningitis**, caused by *Cryptococcus neoformans*. **1. Why the correct answer is right:** In immunocompromised patients, particularly those with advanced HIV/AIDS, the immune system is unable to mount an effective humoral response. Therefore, **antibody detection is unreliable** for diagnosis. Instead, the gold standard for rapid serological diagnosis is the **detection of the cryptococcal capsular polysaccharide antigen (CrAg)**. This antigen is shed in high amounts into the cerebrospinal fluid (CSF) and serum, and can be detected using Latex Agglutination (LA) or Lateral Flow Assays (LFA). **2. Why the incorrect options are wrong:** * **Options A & B (Antibody detection):** As mentioned, AIDS patients are severely immunosuppressed. Testing for antibodies (against capsules or mannoproteins) often yields false negatives because the body cannot produce sufficient antibodies despite a high fungal burden. * **Option D (Cell wall mannoprotein):** While mannoproteins are components of the fungal cell wall, they are not the primary target for routine diagnostic serology in Cryptococcosis. The diagnostic focus is specifically on the **GXM (Glucuronoxylomannan)** component of the polysaccharide capsule. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common fungal meningitis in AIDS:** *Cryptococcus neoformans*. * **Stain of choice:** **India Ink** (shows a clear halo against a dark background due to the capsule). * **Culture:** Sabouraud Dextrose Agar (SDA) – produces mucoid, cream-colored colonies. * **Biochemical test:** Urease positive. * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole for maintenance. * **Opening Pressure:** Characteristically very high in Cryptococcal meningitis.

Question 225: All of the following are dimorphic fungi except:

A. Blastomycoses
B. Cryptococcus (Correct Answer)
C. Histoplasma
D. Paracoccidia

Explanation: **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).

Question 226: Which statement is false regarding Cryptococcus neoformans?

A. Grows at 37°C
B. Has 4 serotypes
C. Urease negative (Correct Answer)
D. Causes infection in immunocompromised patients

Explanation: **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.

Question 227: Which of the following fungi is difficult to isolate on regular Sabouraud Dextrose Agar (SDA) media?

A. Candida
B. Dermatophytes
C. Cryptococcus
D. Malassezia furfur (Correct Answer)

Explanation: **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 228: What is the most common fungus causing chronic meningitis?

A. Blastomyces
B. Cryptococcus neoformans (Correct Answer)
C. Histoplasma
D. Coccidioidomycosis

Explanation: **Explanation:** **Cryptococcus neoformans** is the most common cause of fungal meningitis worldwide. It is an encapsulated yeast typically acquired through the inhalation of basidiospores from soil contaminated with bird (pigeon) droppings. It has a strong predilection for the central nervous system because the cerebrospinal fluid (CSF) lacks the alternative complement pathway components needed for opsonization, and the presence of dopamine in the brain serves as a substrate for the fungus to produce melanin, which protects it from oxidative stress. **Why the other options are incorrect:** * **Blastomyces, Histoplasma, and Coccidioidomycosis:** These are dimorphic fungi that primarily cause pulmonary infections. While they can disseminate to the meninges (especially *Coccidioides* in the Southwestern US), they are significantly less common causes of chronic meningitis compared to *Cryptococcus*, particularly in immunocompromised patients (e.g., those with HIV/AIDS). **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** **India Ink** preparation of CSF shows a characteristic "halo" due to the thick polysaccharide capsule (negative staining). * **Culture:** **Sabouraud Dextrose Agar (SDA)** is the standard; colonies appear mucoid. **Niger Seed Agar** (Birdseed agar) is used to demonstrate melanin production (brown-black colonies). * **Biochemical Test:** It is **Urease positive**. * **Antigen Detection:** The **Lateral Flow Assay (LFA)** or Latex Agglutination for cryptococcal antigen (CrAg) is more sensitive than India Ink. * **Histopathology:** **Mucicarmine stain** specifically stains the capsule red. * **Clinical Sign:** High opening pressure on lumbar puncture is a hallmark of Cryptococcal meningitis.

Question 229: A gardener presents with a subcutaneous lesion on the hand, which he thinks resulted from a wound he received while he was making a sphagnum moss-wire frame for a floral wreath. The nodule has ulcerated and not healed despite use of antibacterial cream, and a new nodule is forming above the original lesion. What is the most likely appropriate treatment for this infection?

A. Oral itraconazole or potassium iodide (Correct Answer)
B. Miconazole cream
C. Clobetasol cream
D. Oral griseofulvin

Explanation: ### Explanation **Diagnosis: Sporotrichosis (Rose Gardener’s Disease)** The clinical presentation describes a classic case of **lymphocutaneous sporotrichosis** caused by the dimorphic fungus *Sporothrix schenckii*. The key diagnostic clues are the occupation (gardener), exposure to **sphagnum moss**, and the characteristic **"sporotrichoid spread"** (nodular lesions ascending along the proximal lymphatics). **1. Why the Correct Answer is Right:** * **Itraconazole:** It is currently the **drug of choice** for cutaneous and lymphocutaneous sporotrichosis due to its superior efficacy and better safety profile compared to older treatments. * **Potassium Iodide (SSKI):** Historically, Saturated Solution of Potassium Iodide (SSKI) was the standard treatment. While its exact mechanism is unclear, it remains a classic, cost-effective alternative mentioned in textbooks and frequently tested in exams. **2. Why the Incorrect Options are Wrong:** * **Miconazole cream (B):** Topical antifungals are ineffective because the infection is subcutaneous and involves the lymphatic system; systemic therapy is required. * **Clobetasol cream (C):** This is a potent corticosteroid. Using steroids on a fungal infection can worsen the condition by suppressing the local immune response. * **Oral griseofulvin (D):** This agent is used for dermatophytoses (skin/hair/nail infections) but has no activity against *Sporothrix*. **3. NEET-PG High-Yield Pearls:** * **Morphology:** *S. schenckii* is a **dimorphic fungus**. At 25°C (mold), it shows "daisy-petal" conidia; at 37°C (yeast), it shows **"cigar-shaped"** bodies. * **Histology:** Look for **Asteroid bodies** (Splendore-Hoeppli phenomenon)—a central yeast cell surrounded by eosinophilic radiating processes. * **Transmission:** Traumatic inoculation (thorns, moss, timber). * **Treatment Tip:** For **disseminated** sporotrichosis, **Amphotericin B** is the drug of choice.

Question 230: The germ tube test is diagnostic for which of the following organisms?

A. Candida albicans (Correct Answer)
B. Cryptococcus neoformans
C. Histoplasma capsulatum
D. Coccidioides

Explanation: **Explanation:** The **Germ Tube Test** (also known as the Reynolds-Braude phenomenon) is a rapid diagnostic test used to identify **Candida albicans** and its close relative, *Candida dubliniensis*. 1. **Why Candida albicans is correct:** When *C. albicans* yeast cells are incubated in human or animal serum at 37°C for 2–3 hours, they produce true hyphae-like extensions called **germ tubes**. A key diagnostic feature is that there is **no constriction** at the point of origin from the parent yeast cell. This test differentiates *C. albicans* from most other *Candida* species (non-albicans Candida), which do not form germ tubes. 2. **Why the other options are incorrect:** * **Cryptococcus neoformans:** This is an encapsulated yeast. It is diagnosed using **India Ink preparation** (to see the capsule), Urease test (positive), and Nitrate assimilation test. It does not form germ tubes. * **Histoplasma capsulatum:** This is a dimorphic fungus. In tissue, it appears as small intracellular yeasts within macrophages. Diagnosis relies on fungal culture (showing "tuberculate macroconidia") or antigen detection. * **Coccidioides:** Another dimorphic fungus, it is characterized by the presence of **spherules containing endospores** in tissue samples, not germ tubes. **High-Yield Clinical Pearls for NEET-PG:** * **False Positives:** *Candida dubliniensis* is also germ tube positive. * **False Negatives:** If the incubation exceeds 3 hours, non-albicans species may produce **pseudohyphae**, which can be mistaken for germ tubes (distinguished by constriction at the origin). * **Culture Media:** *C. albicans* produces **Chlamydospores** on Cornmeal Agar (Dalmau technique), another high-yield diagnostic feature. * **Drug of Choice:** Fluconazole is commonly used, but *C. krusei* is inherently resistant.

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Classification of Fungi

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Superficial Mycoses

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Dermatophytes

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Subcutaneous Mycoses

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Candidiasis

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Aspergillosis

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Cryptococcosis

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Zygomycosis

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Endemic Mycoses

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Opportunistic Fungal Infections

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Antifungal Agents

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Laboratory Diagnosis of Fungal Infections

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Mycology — MCQs

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