Mycology — MCQs
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Vascular invasion is a characteristic feature of which of the following fungal infections?
Confirmation of Cryptococcus species is done by all the following methods except?
The clinical appearance shown in the image is caused by which organism?
Which of the following fungi infects hair, skin, and nails?
The 'cigar body' yeast form is characteristic of which of the following fungal infections?
Which test is used for the diagnosis of Pneumocystis jirovecii?
What is true about Echinococcus Granulosus?
What is the most common causative agent for meningitis in the immunocompromised patient?
Which of the following fungal infections is characterized by vascular involvement and thrombosis?
Meningitis caused by Cryptococcus neoformans is most often acquired by?
Mycology Indian Medical PG Practice Questions and MCQs
Question 361: Vascular invasion is a characteristic feature of which of the following fungal infections?
- A. Candidiasis
- B. Mucormycosis (Correct Answer)
- C. Blastomycosis
- D. Sporotrichosis
Explanation: **Explanation:** **Mucormycosis** (caused by fungi of the order Mucorales, such as *Rhizopus* and *Mucor*) is characterized by **angioinvasion**. The broad, non-septate hyphae have a predilection for invading blood vessel walls. This leads to intravascular thrombosis, distal tissue ischemia, and extensive **hemorrhagic necrosis** (black eschar). This hallmark feature explains why these infections are rapidly progressive and often fatal if not treated with surgical debridement and Amphotericin B. **Analysis of Incorrect Options:** * **Candidiasis:** While *Candida* can cause disseminated infection (candidemia) via the bloodstream, it does not typically exhibit the aggressive vascular wall invasion and subsequent infarction seen in Mucormycosis. * **Blastomycosis:** This is a systemic dimorphic fungus that primarily causes pulmonary infection or chronic granulomatous lesions in the skin and bones. It does not typically present with angioinvasion. * **Sporotrichosis:** Known as "Rose gardener’s disease," it usually presents as a **lymphocutaneous** infection. It spreads via the lymphatic system, forming nodules along the drainage path, rather than invading blood vessels. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Look for broad, **aseptate** hyphae with **right-angled (90°)** branching. (Contrast with *Aspergillus*, which has septate hyphae with acute-angle branching). * **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Ketoacidosis** due to the fungus's ketone reductase enzyme), neutropenia, and deferoxamine therapy. * **Clinical Sign:** The presence of a **black eschar** on the palate or nasal turbinates is a classic board-exam clue for Rhinocerebral Mucormycosis.
Question 362: Confirmation of Cryptococcus species is done by all the following methods except?
- A. Culture on SDA (Sabouraud Dextrose Agar)
- B. Urease test
- C. Mouse Pathogenicity test
- D. Sugar assimilation test (Correct Answer)
Explanation: ### Explanation The question asks for the method that is **NOT** used for the **confirmation** of *Cryptococcus* species. **1. Why "Sugar Assimilation Test" is the correct answer:** While it sounds plausible, the **Sugar Assimilation Test** is actually a standard method used to **differentiate and identify** various species of *Cryptococcus* (e.g., *C. neoformans* vs. *C. albidus*) based on their ability to utilize specific carbohydrates aerobically. Since it is a primary tool for identification and speciation, its inclusion as an "except" option in some classical textbooks suggests a distinction between *identification* and *definitive confirmation* of pathogenicity or genus-level presence. However, in the context of this specific question, it is often highlighted because the other three options are classical "confirmatory" hallmarks taught in medical microbiology. **2. Analysis of Incorrect Options:** * **Culture on SDA:** This is the gold standard for confirming the presence of the fungus. *Cryptococcus* grows as creamy, white, mucoid (due to the capsule) colonies within 48–72 hours. * **Urease Test:** *Cryptococcus* species are characteristically **Urease positive**. This is a rapid confirmatory biochemical test used to distinguish it from other yeasts like *Candida albicans* (which is urease negative). * **Mouse Pathogenicity Test:** This is a definitive confirmatory test for virulence. Intracerebral or intraperitoneal inoculation of the specimen into mice leads to the development of meningitis/brain abscess, confirming the pathogenic nature of the isolate. **High-Yield Clinical Pearls for NEET-PG:** * **Direct Microscopy:** India Ink or Nigrosin preparation shows a **wide, non-staining capsule** (Negative staining). * **Phenol Oxidase/Laccase Activity:** On **Bird Seed Agar (Niger Seed Agar)**, *C. neoformans* produces brown/black pigmented colonies due to melanin production. * **Antigen Detection:** Latex Agglutination test for the capsular polysaccharide antigen is highly sensitive and specific for diagnosis in CSF/Serum. * **Nitrate Reduction:** *C. neoformans* is nitrate negative, helping differentiate it from some other *Cryptococcus* species.
Question 363: The clinical appearance shown in the image is caused by which organism?
- A. Sporothrix schenckii
- B. Paracoccidioides brasiliensis (Correct Answer)
- C. Histoplasma capsulatum
- D. Blastomyces dermatidis
Explanation: ***Paracoccidioides brasiliensis*** - Causes **paracoccidioidomycosis** with pathognomonic **moriform (mulberry) stomatitis** - characteristic granulomatous oral mucosal ulcers with a "mulberry-like" appearance. - Microscopy shows distinctive **"pilot's wheel"** or **"Mickey Mouse head"** yeast morphology with multiple buds around a central mother cell. *Sporothrix schenckii* - Causes **sporotrichosis** typically presenting as **nodular lymphangitic lesions** following trauma (rose gardener's disease). - Oral involvement is rare; usually affects **skin and subcutaneous tissue** in a linear ascending pattern. *Histoplasma capsulatum* - Causes **histoplasmosis** with primary **pulmonary involvement** and occasional **oral ulcers** that are typically shallow and non-granulomatous. - Microscopy shows **small intracellular yeasts** within macrophages, not the characteristic morphology seen here. *Blastomyces dermatitidis* - Causes **blastomycosis** with **verrucous skin lesions** and pulmonary involvement, but oral lesions are uncommon. - Shows **broad-based budding yeasts** with thick walls, distinct from the multiple budding pattern of P. brasiliensis.
Question 364: Which of the following fungi infects hair, skin, and nails?
- A. Trichosporum
- B. Trichophyton (Correct Answer)
- C. Microsporum
- D. Epidermophyton
Explanation: ### Explanation The question pertains to **Dermatophytes**, a group of fungi that require keratin for growth and cause superficial infections (Tinea). They are classified into three main genera based on the tissues they infect: **Trichophyton, Microsporum, and Epidermophyton.** **1. Why Trichophyton is correct:** *Trichophyton* is the only genus among the three that has the enzymatic capability to infect all three keratinized tissues: **Hair, Skin, and Nails.** It is the most common cause of athlete's foot (Tinea pedis) and nail infections (Onychomycosis). **2. Analysis of Incorrect Options:** * **Microsporum (Option C):** This genus infects **Hair and Skin** but typically **spares the nails**. It is characterized by large, spindle-shaped macroconidia. * **Epidermophyton (Option D):** This genus infects **Skin and Nails** but **spares the hair**. It produces club-shaped macroconidia and lacks microconidia. * **Trichosporon (Option A):** This is a yeast-like fungus responsible for **White Piedra** (superficial infection of the hair shaft). It is not classified as a dermatophyte and does not typically involve the skin and nails in the same manner. **3. NEET-PG High-Yield Pearls:** * **Mnemonic for Tissue Involvement:** * **T**richophyton: **T**hree (Hair, Skin, Nails) * **M**icrosporum: **M**inus nails (Hair, Skin) * **E**pidermophyton: **E**xcludes hair (Skin, Nails) * **Wood’s Lamp Examination:** *Microsporum* species (like *M. canis*) show a brilliant green fluorescence, whereas *Trichophyton* species (except *T. schoenleinii*) generally do not fluoresce. * **Culture:** Dermatophytes are typically grown on **Sabouraud Dextrose Agar (SDA)** with Actidione (Cycloheximide).
Question 365: The 'cigar body' yeast form is characteristic of which of the following fungal infections?
- A. Cryptococcosis
- B. Histoplasmosis
- C. Sporotrichosis (Correct Answer)
- D. Aspergillosis
Explanation: **Explanation:** **Sporotrichosis** is the correct answer because it is caused by the dimorphic fungus *Sporothrix schenckii*. In its parasitic (tissue) phase at 37°C, it typically appears as **"cigar-shaped" budding yeast cells**. These elongated, fusiform bodies are a classic histopathological hallmark used to identify the pathogen in tissue biopsies or cultures. **Analysis of Incorrect Options:** * **A. Cryptococcosis:** Characterized by spherical, budding yeast cells surrounded by a thick **polysaccharide capsule**, best visualized with India Ink (halos) or Mucicarmine stain. * **B. Histoplasmosis:** Presents as small, oval yeast cells typically found **inside macrophages**. They do not exhibit the elongated "cigar" morphology. * **C. Aspergillosis:** This is a monomorphic mold, not a yeast. It is characterized by **septate hyphae with acute-angle (45°) branching**, not yeast bodies. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Classically associated with traumatic inoculation from soil, moss, or rose thorns (**"Rose Gardener’s Disease"**). * **Clinical Presentation:** Features a primary nodule at the site of entry followed by linear nodules along the lymphatic drainage (**Sporotrichoid/Lymphocutaneous spread**). * **Asteroid Bodies:** In tissue, yeast cells may be surrounded by eosinophilic radiating processes (Splendore-Hoeppli phenomenon), known as Asteroid bodies. * **Culture:** At 25°C, it produces a "flower-like" or **"daisy-head"** arrangement of conidia. * **Treatment:** Drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.
Question 366: Which test is used for the diagnosis of Pneumocystis jirovecii?
- A. Methenamine silver stain
- B. Polymerase chain reaction (PCR)
- C. Immunofluorescence assay
- D. All of the above (Correct Answer)
Explanation: **Explanation:** *Pneumocystis jirovecii* is an atypical fungus that causes opportunistic pneumonia (PCP), primarily in immunocompromised patients such as those with HIV/AIDS. Diagnosis relies on a combination of staining, molecular techniques, and immunological assays because the organism **cannot be cultured** in routine clinical laboratories. 1. **Methenamine Silver Stain (Gomori/GMS):** This is the gold standard staining method. It specifically stains the **cyst wall** black/brown, revealing characteristic "crushed ping-pong ball" or crescent-shaped cysts. Other stains used include Giemsa (stains trophozoites) and Toluidine blue O. 2. **Polymerase Chain Reaction (PCR):** PCR is highly sensitive and is increasingly used to detect *P. jirovecii* DNA in respiratory specimens like Bronchoalveolar Lavage (BAL) or induced sputum. It is particularly useful when the fungal load is low. 3. **Direct Immunofluorescence Assay (DFA):** This uses monoclonal antibodies tagged with fluorescent dye to bind to *P. jirovecii* antigens. It offers higher sensitivity than conventional stains (like GMS) because it detects both cysts and trophozoites. Since all three modalities are established diagnostic tools, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen of choice:** Bronchoalveolar Lavage (BAL) is superior to induced sputum (90% vs. 50-60% sensitivity). * **Radiology:** Characterized by bilateral "ground-glass opacities" or perihilar infiltrates. * **Biomarker:** Elevated **(1,3)-beta-D-glucan** (BDG) in serum is a highly sensitive but non-specific marker for PCP. * **Treatment:** Drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if $PaO_2 < 70$ mmHg.
Question 367: What is true about Echinococcus Granulosus?
- A. Definitive host in humans
- B. Accidental intermediate host in humans (Correct Answer)
- C. Intermediate host in dogs
- D. Definitive host in snails
Explanation: ### Explanation: Echinococcus Granulosus *Echinococcus granulosus*, the causative agent of **Cystic Echinococcosis (Hydatid Disease)**, follows a complex life cycle involving two hosts. The classification of hosts depends on where the parasite reaches sexual maturity. **1. Why the Correct Answer is Right:** * **Accidental Intermediate Host (Humans):** Humans acquire the infection by ingesting eggs (hexacanth embryos) through contaminated food, water, or direct contact with dogs. In humans, the larvae develop into **hydatid cysts** (asexual stage), but the cycle ends there because humans are rarely eaten by the definitive host. Thus, humans are considered **"dead-end" or accidental intermediate hosts.** **2. Analysis of Incorrect Options:** * **Option A & C:** The **Definitive Host is the Dog** (and other canids). This is where the adult worm lives in the small intestine and undergoes sexual reproduction. * **Option C (revisited):** The **Intermediate Host is the Sheep** (and other herbivores). They ingest eggs from pasture, and the larval stage (hydatid cyst) develops in their organs. * **Option D:** Snails serve as intermediate hosts for Trematodes (Flukes), such as *Schistosoma* or *Fasciola*, not Cestodes like *Echinococcus*. **3. NEET-PG High-Yield Clinical Pearls:** * **Most Common Site:** Liver (Right lobe > Left lobe), followed by the Lungs. * **Diagnosis:** "Eggshell calcification" on X-ray/CT; **Casoni’s test** (immediate hypersensitivity - now largely replaced by ELISA). * **Microscopy:** Presence of **"Hydatid Sand"** (brood capsules and protoscolices) in the cyst fluid. * **Management:** **PAIR** (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration). * **Complication:** Rupture of the cyst can lead to fatal **Anaphylaxis**.
Question 368: What is the most common causative agent for meningitis in the immunocompromised patient?
- A. Histoplasmosis
- B. Cryptococcus (Correct Answer)
- C. Candida albicans
- D. Coccidiomycosis
Explanation: **Explanation:** **Cryptococcus neoformans** is the most common cause of fungal meningitis in immunocompromised individuals, particularly those with HIV/AIDS (typically when CD4 counts fall below 100 cells/µL). The fungus is an encapsulated yeast found in soil enriched with pigeon droppings. Infection occurs via inhalation, followed by hematogenous spread to the meninges due to the organism's strong neurotropism. **Why the other options are incorrect:** * **Histoplasmosis:** While it can disseminate in immunocompromised hosts, it primarily affects the reticuloendothelial system (liver, spleen, bone marrow). Meningitis is a rare complication compared to Cryptococcosis. * **Candida albicans:** Though a common cause of nosocomial fungemia and oral thrush, it rarely causes primary meningitis. When it does, it is usually associated with neurosurgical procedures or indwelling shunts rather than general immunosuppression. * **Coccidiomycosis:** Known as "Valley Fever," it can cause chronic meningitis, but it is geographically restricted (endemic to the Southwestern US) and less common globally than Cryptococcus. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The gold standard is the **Cryptococcal Antigen (CrAg) test** (Latex agglutination) of CSF or serum. * **Microscopy:** **India Ink** preparation shows a characteristic "halo" due to the thick polysaccharide capsule. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)**; produces urease (Urease positive). * **Pathology:** On H&E stain, it shows "soap bubble" appearance in the brain parenchyma. Mucicarmine stain specifically highlights the capsule red. * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by maintenance with Fluconazole.
Question 369: Which of the following fungal infections is characterized by vascular involvement and thrombosis?
- A. Coccidiodomycosis
- B. Aspergillosis
- C. Mucormycosis (Correct Answer)
- D. Histoplasmosis
Explanation: **Explanation:** The hallmark of **Mucormycosis** (caused by fungi of the order Mucorales, such as *Rhizopus* and *Mucor*) is **angioinvasion**. The broad, non-septate hyphae characteristically invade the walls of blood vessels, leading to vasculitis, endothelial damage, and subsequent **thrombosis**. This vascular occlusion results in extensive tissue ischemia and **necrosis**, clinically manifesting as the classic "black eschar" seen in rhino-orbital-cerebral infections. **Analysis of Incorrect Options:** * **Aspergillosis (Option B):** While *Aspergillus* is also angioinvasive (especially in neutropenic patients), the question asks for the infection most classically defined by this feature. In the context of NEET-PG, Mucormycosis is the primary association for rapid thrombosis and necrosis. * **Coccidioidomycosis (Option A) & Histoplasmosis (Option D):** These are systemic dimorphic fungal infections. They typically present as granulomatous diseases (similar to tuberculosis) and primarily involve the reticuloendothelial system or lungs, rather than demonstrating primary angioinvasion and thrombosis. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Diabetic Ketoacidosis** due to ketone reductase activity) and immunosuppression (e.g., post-transplant, COVID-19 steroids). * **Microscopy:** Look for **broad, ribbon-like, non-septate hyphae** with **branching at right angles (90°)**. * **Treatment:** Surgical debridement is critical due to poor drug delivery into necrotic (thrombosed) tissue. Medical management involves **Liposomal Amphotericin B**.
Question 370: Meningitis caused by Cryptococcus neoformans is most often acquired by?
- A. Head trauma
- B. Primary gastrointestinal infection
- C. Hematogenous spread of fungus from the lung (Correct Answer)
- D. Orthopedic surgery
Explanation: **Explanation:** **Cryptococcus neoformans** is an encapsulated yeast primarily found in soil enriched with **pigeon droppings**. The pathogenesis of cryptococcal meningitis follows a specific sequence: inhalation, pulmonary colonization, and subsequent dissemination. 1. **Why Option C is correct:** The primary portal of entry is the **respiratory tract**. Basidiospores or desiccated yeast cells are inhaled into the lungs. In immunocompromised individuals (especially those with HIV/AIDS where CD4 counts are <100 cells/µL), the fungus evades local immune responses and undergoes **hematogenous dissemination**. It has a specific tropism for the Central Nervous System (CNS), crossing the blood-brain barrier to cause subacute or chronic meningitis. 2. **Why other options are incorrect:** * **A & D (Head trauma/Orthopedic surgery):** These are common routes for bacterial infections (e.g., *Staphylococcus aureus*) or certain molds, but *Cryptococcus* is not a commensal of the skin or a common environmental contaminant of surgical suites. * **B (Gastrointestinal):** Unlike certain parasites or enteric bacteria, *Cryptococcus* is not acquired via the fecal-oral route or GI colonization. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **polysaccharide capsule** (Glucuronoxylomannan) is the most important virulence factor; it inhibits phagocytosis. * **Diagnosis:** * **India Ink:** Shows a "halo" (negative staining) due to the capsule. * **Culture:** Niger seed agar (Bird seed agar) produces brownish-black colonies due to **phenoloxidase** activity. * **Antigen Detection:** Lateral Flow Assay (LFA) for cryptococcal antigen (CrAg) is the most sensitive rapid test. * **Stains:** Mucicarmine (stains capsule red), Masson-Fontana (stains melanin in cell wall). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.
Practice by Chapter
Classification of Fungi
Practice Questions
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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