Mycology — MCQs
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What is the causative microorganism of chromoblastomycosis?
A 45-year-old immunosuppressed patient with uncontrolled diabetes mellitus presents with locally destructive lesions that have eroded into the eye, palate, and central nervous system, often originating from the sinuses. The causative organism can be difficult to culture. What is the appropriate treatment for this condition?
Which of the following fungi are called BLACK YEASTS?
In tissue, Coccidioides immitis produces what structures?
Which of the following fungal phyla lacks a sexual phase?
Cryptococcus neoformans is visualized by which method?
What is the most common candidal species infecting neonates transmitted from a caregiver's hand?
Ectothrix infection is caused by which of the following fungi?
Cryptococcus can be readily demonstrated by which stain?
Tuberculate spores are diagnostic in which of the following conditions?
Mycology Indian Medical PG Practice Questions and MCQs
Question 41: What is the causative microorganism of chromoblastomycosis?
- A. Cladosporium (Correct Answer)
- B. Blastomyces
- C. Sporothrix
- D. Histoplasma capsulatum
Explanation: **Explanation:** **Chromoblastomycosis** is a chronic fungal infection of the skin and subcutaneous tissue, typically occurring after traumatic inoculation (e.g., a thorn prick) with pigmented fungi found in soil and decaying vegetation. **Why Cladosporium is correct:** The causative agents of chromoblastomycosis are a group of **dematiaceous (melanized/dark-walled) fungi**. The most common genera involved include ***Cladosporium*** (specifically *Cladosporium carrionii*), *Fonsecaea pedrosoi* (most common worldwide), and *Phialophora verrucosa*. A hallmark diagnostic feature seen in tissue biopsy is the presence of **Sclerotic bodies** (also known as Medlar bodies or "copper pennies")—thick-walled, dark brown, multiseptate fungal cells. **Why the other options are incorrect:** * **Blastomyces:** Causes Blastomycosis, a systemic dimorphic fungal infection. It typically presents with pulmonary symptoms or disseminated skin lesions characterized by broad-based budding yeast, not sclerotic bodies. * **Sporothrix:** Causes Sporotrichosis ("Rose gardener’s disease"). It presents with nodules following lymphatic drainage (sporotrichoid spread) and is characterized by cigar-shaped yeast cells and Asteroid bodies. * **Histoplasma capsulatum:** A systemic dimorphic fungus causing Histoplasmosis. It is an intracellular pathogen found within macrophages, primarily affecting the lungs and reticuloendothelial system. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** "Cauliflower-like" verrucous (warty) lesions, usually on the lower extremities. * **Pathognomonic Sign:** **Sclerotic bodies / Medlar bodies** (Copper penny appearance). * **Culture:** Dematiaceous fungi produce velvety, dark-colored (olive-black) colonies. * **Treatment:** Itraconazole or Terbinafine; often requires surgical excision for small lesions.
Question 42: A 45-year-old immunosuppressed patient with uncontrolled diabetes mellitus presents with locally destructive lesions that have eroded into the eye, palate, and central nervous system, often originating from the sinuses. The causative organism can be difficult to culture. What is the appropriate treatment for this condition?
- A. Intravenous amphotericin only
- B. Surgical debridement only
- C. Watchful observation
- D. Intravenous amphotericin with strong consideration for surgical debridement (Correct Answer)
Explanation: This clinical presentation is classic for **Rhinocerebral Mucormycosis**, a life-threatening opportunistic fungal infection caused by members of the order Mucorales (e.g., *Rhizopus*, *Mucor*). ### **Why Option D is Correct** Mucormycosis is characterized by **angioinvasion**, leading to extensive tissue necrosis and thrombosis. Because the fungi invade blood vessels, systemic antifungal drugs often cannot reach the site of infection in therapeutic concentrations. Therefore, the gold standard of management is a **dual approach**: 1. **Medical:** High-dose **Liposomal Amphotericin B** is the drug of choice to inhibit fungal growth. 2. **Surgical:** Urgent and aggressive **surgical debridement** of all necrotic tissue is mandatory to reduce the fungal burden and allow the antifungal medication to reach the viable tissue interface. ### **Why Other Options are Incorrect** * **Option A:** Amphotericin alone is insufficient because it cannot penetrate necrotic, avascular tissue effectively. * **Option B:** Surgery alone is inadequate as the infection is invasive and microscopic fungal elements will remain, leading to rapid recurrence. * **Option C:** This condition is a medical emergency with a high mortality rate; observation is contraindicated. ### **NEET-PG High-Yield Pearls** * **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Ketoacidosis**—the fungi thrive in acidic, glucose-rich environments) and neutropenia. * **Microscopy:** Look for **broad, ribbon-like, aseptate hyphae** with **wide-angle (90°) branching**. * **Clinical Sign:** A characteristic **black eschar** on the palate or nasal turbinates. * **Culture:** Often difficult; the fungi are fragile and can be crushed during tissue processing (non-viable on culture). * **First-line Drug:** Liposomal Amphotericin B. **Isavuconazole** or **Posaconazole** are used as step-down or salvage therapy.
Question 43: Which of the following fungi are called BLACK YEASTS?
- A. Saccharomyces cereveciae
- B. Exophiala jeanselmei (Correct Answer)
- C. Candida tropicalis
- D. Cryptococcus neoformans
Explanation: **Explanation:** **1. Why Exophiala jeanselmei is correct:** *Exophiala jeanselmei* belongs to a group of fungi known as **Dematiaceous (pigmented) fungi**. These are called **"Black Yeasts"** because they initially grow as dark, mucoid, yeast-like colonies due to the presence of **melanin** in their cell walls. As the colony matures, it develops into a filamentous (mold) form, making it a polymorphic fungus. Clinically, it is a common causative agent of **Phaeohyphomycosis** and **Eumycetoma** (subcutaneous fungal infections). **2. Why the other options are incorrect:** * **Saccharomyces cerevisiae:** Known as "Baker's yeast" or "Brewer's yeast." It is a non-pigmented, budding yeast used extensively in the food industry and as a model organism in genetics. * **Candida tropicalis:** A non-pigmented yeast and a member of the *Candida* genus. It is a common cause of candidemia in neutropenic patients but does not produce melanin or black colonies. * **Cryptococcus neoformans:** While this is an encapsulated yeast that produces melanin (visible on **Niger Seed Agar/Bird Seed Agar**), it is traditionally classified as a **Basidiomycetous yeast**, not a "Black Yeast." The term "Black Yeast" is specifically reserved for dematiaceous fungi like *Exophiala* and *Hortaea*. **3. NEET-PG High-Yield Pearls:** * **Black Yeasts:** Key examples include *Exophiala jeanselmei*, *Hortaea werneckii* (causes Tinea nigra), and *Wangiella dermatitidis*. * **Melanin:** Acts as a virulence factor by protecting the fungus against host immune responses (oxidative burst) and UV radiation. * **Fontana-Masson Stain:** This stain is used to detect melanin in the cell walls of dematiaceous fungi in tissue sections. * **Clinical Presentation:** *Exophiala* species often present as painless, slow-growing subcutaneous nodules or cysts following traumatic inoculation (e.g., a thorn prick).
Question 44: In tissue, Coccidioides immitis produces what structures?
- A. Spherules and endospores (Correct Answer)
- B. Encapsulated yeast cells
- C. Fine, delicate hyphae
- D. Coarse, septate hyphae
Explanation: **Explanation:** *Coccidioides immitis* is a **dimorphic fungus** that exhibits a unique life cycle. Unlike most other dimorphic fungi (which exist as mold in the environment and yeast in tissue), *Coccidioides* does not form yeast cells in the human body. **1. Why Option A is Correct:** In the soil (saprophytic phase), the fungus forms infectious **arthroconidia**. Once inhaled into the warm, moist environment of the lungs (parasitic phase), these arthroconidia transform into large, thick-walled structures called **spherules** (20–100 µm). Inside these spherules, the cytoplasm undergoes progressive cleavage to produce hundreds of **endospores**. When the spherule ruptures, the endospores are released, and each can potentially develop into a new spherule. **2. Why the other options are incorrect:** * **Option B (Encapsulated yeast cells):** This is the characteristic morphology of *Cryptococcus neoformans*. * **Option C (Fine, delicate hyphae):** This describes Actinomycetes (like *Nocardia* or *Actinomyces*), which are filamentous bacteria, not fungi. * **Option D (Coarse, septate hyphae):** This is typical of *Aspergillus* species (showing acute-angle branching) or the saprophytic mold phase of dimorphic fungi, but not the tissue phase of *Coccidioides*. **Clinical Pearls for NEET-PG:** * **Geographic Niche:** Found in the Southwestern USA (San Joaquin Valley), Mexico, and Central/South America. * **Disease:** Known as **Valley Fever** or Desert Rheumatism. * **Infectivity:** It is highly infectious; even a single arthroconidium can cause disease. It is a significant laboratory hazard. * **Diagnosis:** Identification of spherules in KOH mount or biopsy is definitive. On Sabouraud Dextrose Agar (SDA), it grows as a mold with **barrel-shaped arthroconidia** showing alternate staining (disjunctor cells).
Question 45: Which of the following fungal phyla lacks a sexual phase?
- A. Deuteromycota (Correct Answer)
- B. Basidiomycota
- C. Ascomycota
- D. Zygomycota
Explanation: ### Explanation **Correct Answer: A. Deuteromycota** **1. Why Deuteromycota is correct:** Deuteromycota, commonly known as **"Fungi Imperfecti,"** is a taxonomic group defined by the **absence of a known sexual cycle** (teleomorph). These fungi reproduce exclusively through asexual means, such as conidia or budding (anamorph). In medical mycology, many human pathogens were historically placed here until their sexual stages were discovered, at which point they were reclassified into other phyla. **2. Why the other options are incorrect:** * **B. Basidiomycota:** These are "Club fungi" (e.g., *Cryptococcus*). They possess a sexual phase characterized by the production of **basidiospores** on a club-shaped structure called a basidium. * **C. Ascomycota:** These are "Sac fungi" (e.g., *Aspergillus*, *Histoplasma*). They undergo sexual reproduction resulting in the formation of **ascospores** within a sac-like structure called an ascus. This is the largest phylum of medically important fungi. * **D. Zygomycota:** These are "Lower fungi" (e.g., *Rhizopus*, *Mucor*). They reproduce sexually by the fusion of gametangia to form thick-walled, resistant **zygospores**. **3. NEET-PG High-Yield Clinical Pearls:** * **Taxonomic Shift:** Many fungi are being renamed as their sexual stages are identified. For example, the teleomorph (sexual state) of *Ajellomyces* corresponds to the anamorph (asexual state) of *Histoplasma*. * **Asexual Spores:** In the clinical lab, we identify fungi primarily by their **asexual structures** (e.g., macroconidia in Dermatophytes), as sexual structures are rarely seen in clinical specimens. * **Mnemonic:** **D**euteromycota = **D**evoid of sexual stage (**D**ormant sex life).
Question 46: Cryptococcus neoformans is visualized by which method?
- A. India ink preparation (Correct Answer)
- B. Giemsa stain
- C. Gram stain
- D. Acid-fast stain
Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast characterized by a thick, polysaccharide capsule. The **India ink preparation** is the classic "negative staining" technique used for its identification. Because the capsule is non-ionic, it does not take up the ink particles; instead, the ink creates a dark background, making the clear, halo-like capsule stand out around the budding yeast cells. This is a rapid bedside test for diagnosing Cryptococcal meningitis in CSF samples. **Analysis of Incorrect Options:** * **Giemsa stain:** Primarily used for intracellular pathogens (like *Histoplasma*) or blood parasites (like *Plasmodium*). It does not highlight the Cryptococcal capsule. * **Gram stain:** *Cryptococcus* typically appears Gram-positive (purple), but the staining is often irregular or "mottled," and the capsule is not clearly visualized, making it unreliable for definitive identification. * **Acid-fast stain:** Used for Mycobacteria and certain Nocardia species. *Cryptococcus* is not acid-fast (though *Cryptococcus* can occasionally be weakly positive in modified stains, it is not the standard diagnostic method). **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The polysaccharide capsule (GXM - Glucuronoxylomannan) is the primary virulence factor; it inhibits phagocytosis. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as mucoid, cream-colored colonies. **Niger Seed Agar** (Birdseed agar) is specific, where it produces brown-black colonies due to phenoloxidase activity. * **Most Sensitive Test:** While India ink is specific, the **Cryptococcal Antigen (CrAg)** detection via Lateral Flow Assay (LFA) or Latex Agglutination is more sensitive. * **Histopathology:** The capsule can be stained specifically with **Mucicarmine** (bright red) or PAS.
Question 47: What is the most common candidal species infecting neonates transmitted from a caregiver's hand?
- A. Candida tropicalis
- B. Candida parapsilosis (Correct Answer)
- C. Candida glabrata
- D. Candida albicans
Explanation: **Explanation:** **Candida parapsilosis** is the correct answer because it is uniquely associated with **exogenous transmission** via the hands of healthcare workers. Unlike most other *Candida* species that are part of the normal human endogenous flora (gut/vagina), *C. parapsilosis* has a high affinity for plastic surfaces and frequently colonizes the skin. In neonatal intensive care units (NICUs), it is a leading cause of catheter-related bloodstream infections and outbreaks, primarily transmitted through direct contact from caregivers' hands to the neonate or medical devices. **Analysis of Incorrect Options:** * **Candida albicans:** While it remains the most common cause of candidiasis overall (including oral thrush and diaper dermatitis in infants), it is typically transmitted **vertically** from the mother’s vaginal flora during birth, rather than exogenously from caregiver hands. * **Candida tropicalis:** This species is more commonly associated with neutropenic patients and malignancy. While it can cause nosocomial infections, it is not the classic "hand-transmitted" species in neonates. * **Candida glabrata:** This species is known for its high resistance to azoles and is more frequently seen in elderly patients or those with prior fluconazole exposure, rather than in the neonatal population. **High-Yield Pearls for NEET-PG:** * **C. parapsilosis:** Key association with **Hyperalimentation (TPN)**, prosthetic devices, and **hand transmission** in NICUs. * **C. albicans:** Most common species; forms **germ tubes** (Reynolds-Braude phenomenon) and chlamydospores on Cornmeal agar. * **C. glabrata:** Non-dimorphic (exists only as yeast); lacks pseudohyphae. * **C. auris:** Emerging multi-drug resistant (MDR) species causing hospital outbreaks; often misidentified in labs.
Question 48: Ectothrix infection is caused by which of the following fungi?
- A. Trichophyton tonsurans
- B. Microsporum audouinii (Correct Answer)
- C. Trichophyton schoenleinii
- D. Trichophyton violaceum
Explanation: **Explanation:** Dermatophytosis of the hair (Tinea capitis) is classified based on how the fungal spores (arthroconidia) invade the hair shaft. **1. Why Microsporum audouinii is correct:** In **Ectothrix infection**, the fungus invades the hair shaft, but the spores form a sheath on the **outside** of the shaft. This process destroys the cuticle. *Microsporum* species (like *M. audouinii* and *M. canis*) are the classic causes of ectothrix infections. Clinically, these present as "Gray Patch" tinea capitis and typically **fluoresce bright greenish-yellow** under Wood’s lamp. **2. Analysis of Incorrect Options:** * **Trichophyton tonsurans & Trichophyton violaceum:** These cause **Endothrix infection**, where spores are found **inside** the hair shaft while the cuticle remains intact. This leads to hair brittleness and breakage at the scalp surface, resulting in the clinical "Black Dot" appearance. They do not fluoresce under Wood’s lamp. * **Trichophyton schoenleinii:** This is the primary agent of **Favus**. It is characterized by **scutula** (crusts) and permanent scarring alopecia. It shows a unique "Favic chandelier" pattern on microscopy and produces an endothrix-like invasion with air bubbles (honeycomb appearance). **3. High-Yield Clinical Pearls for NEET-PG:** * **Ectothrix:** Spores outside; Cuticle destroyed; Wood’s lamp (+) positive; Example: *Microsporum* spp. * **Endothrix:** Spores inside; Cuticle intact; Wood’s lamp (–) negative; Example: *T. tonsurans* (most common cause of Tinea capitis worldwide), *T. violaceum*. * **Wood’s Lamp Fluorescence:** *M. audouinii* and *M. canis* (Green); *T. schoenleinii* (Pale Green/Blue). * **Mnemonic:** **"E"**ctothrix = **"E"**xterior spores; **"En"**dothrix = **"In"**terior spores.
Question 49: Cryptococcus can be readily demonstrated by which stain?
- A. Albert's stain
- B. India ink stain (Correct Answer)
- C. Giemsa's stain
- D. Gram's stain
Explanation: ### Explanation **Correct Answer: B. India Ink Stain** *Cryptococcus neoformans* is an encapsulated yeast. The hallmark of this organism is its **polysaccharide capsule**, which does not take up common dyes. **India ink** (and Nigrosin) acts as a **negative stain**. The carbon particles in the ink are excluded by the thick capsule, creating a clear, translucent halo around the budding yeast cells against a dark background. This is a rapid, bedside diagnostic tool for Cryptococcal meningitis using cerebrospinal fluid (CSF). **Analysis of Incorrect Options:** * **A. Albert’s stain:** Used specifically for demonstrating metachromatic granules (volutin granules) in *Corynebacterium diphtheriae*. * **C. Giemsa’s stain:** A Romanowsky stain primarily used for peripheral blood smears (malaria, leishmania) and certain intracellular bacteria like *Chlamydia* or *Rickettsia*. While it can stain the fungal body, it does not highlight the capsule. * **D. Gram’s stain:** *Cryptococcus* typically appears as Gram-positive (purple) budding yeast, but the stain often appears patchy, and the diagnostic capsule is not clearly visualized, making it unreliable for definitive identification. **High-Yield Clinical Pearls for NEET-PG:** * **Most Sensitive Test:** The **Cryptococcal Antigen (CrAg)** test (Latex agglutination or Lateral Flow Assay) is more sensitive than India ink. * **Culture:** **Sabouraud Dextrose Agar (SDA)** is used; colonies appear creamy/mucoid. * **Other Stains:** **Mucicarmine** (stains the capsule red—highly specific), Masson-Fontana (stains melanin in the cell wall), and PAS/GMS (general fungal stains). * **Clinical Association:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100 cells/µL).
Question 50: Tuberculate spores are diagnostic in which of the following conditions?
- A. Cryptococcosis
- B. Chromomycosis
- C. Sporotrichosis
- D. Histoplasmosis (Correct Answer)
Explanation: **Explanation:** **Histoplasmosis (Option D)** is caused by the dimorphic fungus *Histoplasma capsulatum*. In its saprophytic (mold) phase at 25°C, it produces two types of spores: microconidia and **macroconidia**. The macroconidia are large (8–15 µm), thick-walled, spherical, and characterized by finger-like projections on their surface, giving them a "bumpy" or **tuberculate** appearance. These tuberculate macroconidia are the pathognomonic diagnostic feature seen on Lactophenol Cotton Blue (LPCB) mounts. **Why other options are incorrect:** * **Cryptococcosis (A):** Characterized by round, budding yeast cells with a thick **polysaccharide capsule**, best visualized using India Ink or Mucicarmine stain. It does not produce tuberculate spores. * **Chromomycosis (B):** Diagnosed by the presence of **Sclerotic bodies** (Medlar bodies or "copper pennies"), which are thick-walled, dark brown, septate structures seen in tissue sections. * **Sporotrichosis (C):** Known for "Cigar-shaped" yeast cells in tissue and "flower-like" or **rosette-like** arrangements of conidia on culture. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** *Histoplasma* is found in soil enriched with **bird or bat guano** (caves, chicken coops). * **Intracellular Pathogen:** In the yeast phase (37°C), it is found inside **macrophages** (seen on Giemsa/Wright stain). * **Clinical Mimicry:** It is often called the "Great Mimic" as it clinically and radiologically resembles Tuberculosis (calcified granulomas). * **Treatment:** It is treated with Amphotericin B (severe) or Itraconazole (mild-moderate).
Practice by Chapter
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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