Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 381: Aseptate hyphae and asexual spores are seen with which of the following?

A. Phycomycetes
B. Ascomycetes
C. Fungi imperfecti
D. Zygomycetes (Correct Answer)

Explanation: **Explanation:** The classification of fungi is primarily based on the morphology of their hyphae and the nature of their sexual and asexual reproduction. **1. Why Zygomycetes is correct:** Zygomycetes (which includes *Rhizopus*, *Mucor*, and *Lichtheimia*) are characterized by **aseptate** (coenocytic) hyphae, meaning they lack cross-walls. They reproduce asexually via **sporangiospores** produced within a sac-like structure called a sporangium. Sexually, they produce thick-walled zygospores. In clinical practice, these fungi are known for causing aggressive, angioinvasive infections (Mucormycosis). **2. Why other options are incorrect:** * **Ascomycetes:** These are "sac fungi" (e.g., *Aspergillus*, *Penicillium*). They possess **septate hyphae** and produce asexual spores called conidia. Their sexual spores are ascospores. * **Fungi Imperfecti (Deuteromycetes):** This is a taxonomic "holding category" for fungi that lack a known sexual cycle. While they produce asexual spores (conidia), they typically possess **septate hyphae**. * **Phycomycetes:** This is an older, obsolete taxonomic term that previously grouped Zygomycetes and Oomycetes together. While they share the trait of being aseptate, **Zygomycetes** is the more specific and modern mycological classification used in medical exams. **Clinical Pearls for NEET-PG:** * **Mucormycosis:** Classically presents in diabetic ketoacidosis (DKA) patients as rhino-cerebral infection. * **Histopathology:** Look for "Broad, ribbon-like, aseptate hyphae with wide-angled (90°) branching." (Contrast this with *Aspergillus*, which shows narrow, septate hyphae with acute-angled 45° branching). * **Drug of Choice:** Liposomal Amphotericin B is the primary treatment for Zygomycetes infections.

Question 382: Rhinosporidium seeberi grows in which of the following?

A. SDA (Sabouraud Dextrose Agar)
B. HeLa cell line
C. MacNeal's medium
D. Not cultivable (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Not cultivable** **Why it is correct:** *Rhinosporidium seeberi* is a unique organism that causes **Rhinosporidiosis**, a chronic granulomatous infection of the mucous membranes (primarily the nose). Despite its fungal-sounding name and appearance (producing sporangia), it is currently classified as a **Mesomycetozoean**—a group of aquatic protists located at the evolutionary boundary between animals and fungi. The defining characteristic of *R. seeberi* for competitive exams is that it has **never been successfully cultured in vitro** on any artificial media (like SDA) or standard cell lines. Diagnosis relies entirely on clinical presentation and histopathology (demonstrating large, thick-walled sporangia containing thousands of endospores). **Why other options are incorrect:** * **A. SDA:** This is the standard medium for most pathogenic fungi (e.g., *Candida*, *Aspergillus*). *R. seeberi* does not grow on any synthetic fungal media. * **B. HeLa cell line:** While some obligate intracellular pathogens (like *Chlamydia*) are grown in cell cultures, *R. seeberi* has failed to show sustained growth in human cell lines. * **C. MacNeal's medium (NNN medium):** This is specifically used for cultivating Hemoflagellates like *Leishmania* and *Trypanosoma cruzi*. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Associated with stagnant water; common in sand harvesters and those bathing in ponds. * **Clinical Feature:** "Leaf-like," friable, highly vascular (bleeding) polyps in the nose or nasopharynx. * **Histology:** Large **sporangia** (up to 300 µm) filled with **endospores**. These are much larger than the spherules of *Coccidioides immitis*. * **Treatment:** Surgical excision with cauterization of the base. Dapsone is the only medical therapy with some reported efficacy.

Question 383: Which of the following are neurotropic fungi?

A. Cryptococcus neoformans
B. Histoplasma capsulatum
C. Candida species (Correct Answer)
D. Aspergillus species

Explanation: **Explanation:** The term **neurotropic** refers to the tendency of a pathogen to specifically target or invade the nervous system. While several fungi can cause CNS infections, **Candida species** (particularly *Candida albicans*) are considered highly neurotropic in the context of disseminated candidiasis. 1. **Why Candida is the correct answer:** In cases of systemic candidemia, the brain is one of the most frequently involved organs. Candida has a unique ability to cross the blood-brain barrier (BBB) via both paracellular and transcellular pathways. It often presents as multiple micro-abscesses or small granulomas in the brain parenchyma rather than just meningitis, making it a classic example of a neurotropic fungus in clinical pathology. 2. **Analysis of Incorrect Options:** * **Cryptococcus neoformans:** While it is the most common cause of fungal meningitis (especially in HIV patients), it is technically classified as **basidiomycetous yeast** with a predilection for the CNS. However, in standard microbiological classification for this specific question type, Candida is prioritized for its invasive neurotropic properties during dissemination. * **Histoplasma capsulatum:** This is a dimorphic fungus that primarily causes pulmonary disease. CNS involvement (Chronic meningitis) occurs in less than 5-10% of disseminated cases. * **Aspergillus species:** These are **angioinvasive** fungi. They cause CNS disease primarily through vascular infarction and thrombosis (leading to stroke or large abscesses) rather than true neurotropism. **High-Yield Clinical Pearls for NEET-PG:** * **Most common fungal meningitis in AIDS:** *Cryptococcus neoformans* (Diagnosis: India Ink, Mucicarmine stain, CrAg test). * **Most common cause of fungal brain abscess:** *Aspergillus* (due to angioinvasion). * **Rhino-oculocerebral mucormycosis:** Seen in Diabetic Ketoacidosis (DKA) patients; caused by *Rhizopus* (Broad, non-septate hyphae). * **Candida CNS infection:** Often presents as "Micro-abscesses" in neutropenic patients.

Question 384: A HIV-positive female presents with an indurated ulcer over the tongue. Laboratory findings show growth in cornmeal agar at 20°C, microscopy showing hyphae, and growth in human serum at 37°C showing budding yeasts. What is the probable causative agent?

A. Candida albicans (Correct Answer)
B. Histoplasmosis
C. Blastomycosis
D. Coccidioidomycosis

Explanation: ### Explanation The correct answer is **Candida albicans**. This question tests your ability to recognize the specific morphological transitions and laboratory diagnostic features of *Candida*. **Why Candida albicans is correct:** * **Clinical Context:** HIV-positive patients are highly susceptible to opportunistic infections like oral candidiasis (thrush) and esophageal candidiasis. * **Cornmeal Agar (20°C):** This is the specific medium used to induce the formation of **chlamydospores** (thick-walled resting spores) and pseudohyphae/true hyphae in *C. albicans*, which is a diagnostic hallmark. * **Human Serum (37°C):** When incubated in human serum for 2–3 hours, *C. albicans* produces **germ tubes** (Reynolds-Braude phenomenon). These appear as elongated protrusions from the yeast cell without a constriction at the base. * **Dimorphism:** While most fungi are either yeasts or molds, *Candida* is unique as it can exist as budding yeasts, pseudohyphae, and true hyphae depending on environmental conditions. **Why the other options are incorrect:** * **Histoplasmosis:** While it causes oral ulcers in HIV patients, it is a **systemic dimorphic fungus**. In the body (37°C), it appears as small intracellular yeasts within macrophages, not hyphae. * **Blastomycosis:** Characterized by **broad-based budding yeasts** at 37°C. It typically presents with pulmonary or skin lesions rather than isolated tongue ulcers in this laboratory context. * **Coccidioidomycosis:** Identified by **spherules containing endospores** in tissue samples at 37°C, not budding yeasts or hyphae. **NEET-PG High-Yield Pearls:** * **Germ Tube Test:** The most rapid method to identify *C. albicans*. * **Chromogenic Agar (CHROMagar):** Used to differentiate species (e.g., *C. albicans* is green, *C. tropicalis* is blue). * **C. glabrata:** Notable for being germ tube negative and often resistant to azoles. * **C. auris:** An emerging multi-drug resistant (MDR) pathogen in ICU settings.

Question 385: All of the following are true regarding Cryptococcus neoformans except?

A. Affects immunocompromised patients
B. Grown on Sabouraud's agar
C. Capsular antigen can be detected in the CSF
D. Anticapsular antibody is protective (Correct Answer)

Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that primarily causes meningitis. The key to understanding this question lies in the host's immune response to the fungus. **Why Option D is the correct answer (False statement):** In Cryptococcosis, the **cell-mediated immunity (CMI)**—specifically T-cells and macrophages—is the primary defense mechanism. While the body does produce antibodies against the polysaccharide capsule, these **anticapsular antibodies are NOT protective**. They do not aid in clearing the infection, which is why patients with impaired CMI (like those with HIV/AIDS) are highly susceptible regardless of antibody levels. **Analysis of Incorrect Options (True statements):** * **Option A:** It is a classic **opportunistic pathogen**. While it can affect healthy individuals, it most severely affects immunocompromised patients, particularly those with CD4 counts <100 cells/µL. * **Option B:** Like most fungi, *Cryptococcus* grows well on **Sabouraud’s Dextrose Agar (SDA)**, appearing as mucoid, cream-colored colonies. It also grows on Bird Seed Agar (Niger seed agar), producing melanin. * **Option C:** Detection of the **capsular polysaccharide antigen (CrAg)** via Latex Agglutination or Lateral Flow Assay (LFA) in the CSF or serum is a highly sensitive and specific diagnostic gold standard. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Spherical budding yeast with a wide polysaccharide capsule (demonstrated by **India Ink** as a clear halo). * **Virulence Factor:** The capsule is the most important; **Phenoloxidase enzyme** (melanin production) is another. * **Source:** Pigeon droppings and soil. * **Stains:** Mucicarmine (stains capsule red), Fontana-Masson (stains melanin). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Question 386: What is the likely cause of this manifestation?

A. Candida
B. Pseudomonas (Correct Answer)
C. Staphylococcus aureus
D. Fusarium

Explanation: ***Pseudomonas*** - **Ecthyma gangrenosum** is the classic skin manifestation of **Pseudomonas aeruginosa** infection, particularly in **immunocompromised patients**. - Presents as **necrotic ulcerative lesions** with a characteristic **black eschar** and surrounding erythematous halo, often in the gluteal or perineal region. *Candida* - Typically causes **mucocutaneous infections** like oral thrush, vulvovaginitis, or **intertrigo** in warm, moist areas. - Skin lesions appear as **erythematous patches** with satellite pustules, not necrotic ulcers with black eschars. *Staphylococcus aureus* - Causes **pyogenic skin infections** like **cellulitis**, **impetigo**, or **folliculitis** with purulent discharge. - Lesions are typically **pustular** or **honey-crusted** rather than the necrotic, gangrenous appearance seen in ecthyma gangrenosum. *Fusarium* - A **filamentous fungus** that can cause **necrotizing skin infections** in immunocompromised patients, but less commonly than Pseudomonas. - Skin lesions may be **nodular** or **ulcerative** but lack the characteristic appearance of ecthyma gangrenosum.

Question 387: Which of the following are endemic fungal infections?

A. Coccidioides immitis (Correct Answer)
B. Cryptococcus
C. Histoplasmosis
D. Aspergillus

Explanation: ### Explanation **Endemic mycoses** are fungal infections caused by **dimorphic fungi** that are geographically restricted to specific ecological niches. These fungi exist as molds in the environment (soil) and transform into yeasts (or spherules) at body temperature (37°C) upon inhalation. **1. Why Coccidioides immitis is correct:** *Coccidioides immitis* (and *C. posadasii*) is a classic endemic fungus found primarily in the Southwestern United States (San Joaquin Valley) and parts of Central/South America. It causes **Coccidioidomycosis** (Valley Fever). Along with *Histoplasma capsulatum*, *Blastomyces dermatitidis*, and *Paracoccidioides brasiliensis*, it forms the core group of systemic endemic mycoses. **2. Analysis of Incorrect Options:** * **B. Cryptococcus:** This is an **opportunistic** fungus, not endemic. While *C. neoformans* is found worldwide (ubiquitous in pigeon droppings), it primarily affects immunocompromised hosts (e.g., HIV/AIDS). It is a monomorphic yeast (not dimorphic). * **C. Histoplasmosis:** While *Histoplasma* **is** an endemic fungus, in the context of single-choice questions where only one "best" answer is marked (as per your prompt), *Coccidioides* is often the prototype. *Note: In many exams, both A and C would be considered correct unless the question specifies a particular region.* * **D. Aspergillus:** This is a ubiquitous **opportunistic mold**. It is found globally in decaying vegetation and air. It is monomorphic (always a mold with septate hyphae branching at 45°). **3. NEET-PG High-Yield Pearls:** * **Dimorphism Rule:** "Mold in the Cold (25°C), Yeast in the Heat (37°C)." * **Exception:** *Coccidioides* is dimorphic but forms **spherules** containing endospores in the tissue, not yeasts. * **Histoplasmosis:** Associated with bat guano/bird droppings; mimics TB on imaging. * **Blastomycosis:** Characterized by "Broad-Based Budding" yeasts. * **Paracoccidioidomycosis:** Characterized by the "Pilot’s Wheel" appearance.

Question 388: Candidiasis is a complication of all of the following except?

A. Prolonged antibiotic therapy
B. Corticosteroid therapy
C. Immunocompromised disease
D. Aspiration pneumonia (Correct Answer)

Explanation: **Explanation:** The correct answer is **Aspiration pneumonia**. **1. Why Aspiration Pneumonia is the Correct Answer:** Aspiration pneumonia is typically caused by the inhalation of oropharyngeal or gastric contents into the lower respiratory tract. The primary pathogens involved are **anaerobic bacteria** (e.g., *Bacteroides*, *Fusobacterium*) and aerobic bacteria (e.g., *S. pneumoniae*, *K. pneumoniae*). Candidiasis is not a recognized complication of aspiration pneumonia because the pathophysiology involves chemical irritation and bacterial infection rather than fungal overgrowth. **2. Analysis of Incorrect Options:** * **Prolonged Antibiotic Therapy:** Broad-spectrum antibiotics suppress the normal bacterial flora (e.g., *Lactobacillus*), which usually keeps *Candida* in check. This loss of competition leads to fungal overgrowth, causing oral thrush or vaginal candidiasis. * **Corticosteroid Therapy:** Steroids are immunosuppressive. They inhibit T-cell function and neutrophil activity, reducing the body's ability to fight opportunistic infections like *Candida*. * **Immunocompromised Disease:** Conditions like HIV/AIDS (where CD4 counts drop), diabetes mellitus, and neutropenia are classic risk factors. *Candida* is an opportunistic pathogen that thrives when the host's cellular immunity is impaired. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Candida albicans* is unique because it shows **pseudohyphae** at 37°C and **Germ tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C for 2 hours. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as creamy white, smooth colonies with a "yeasty" odor. * **Chronic Mucocutaneous Candidiasis (CMC):** Associated with T-cell defects and endocrine abnormalities. * **Drug of Choice:** Fluconazole for superficial infections; Echinocandins (e.g., Caspofungin) or Amphotericin B for systemic/invasive candidiasis.

Question 389: Darlings disease is:

A. Histoplasmosis (Correct Answer)
B. Phycomycosis
C. Actinomycosis
D. Bleomycosis

Explanation: **Explanation:** **Histoplasmosis (Option A)** is known as **Darling’s disease**, named after Samuel Taylor Darling who first described the pathogen in 1905. It is caused by the dimorphic fungus *Histoplasma capsulatum*. The fungus is typically found in soil enriched with bird or bat droppings (guano). In humans, it primarily affects the reticuloendothelial system, often presenting as a pulmonary infection that can mimic tuberculosis. **Why other options are incorrect:** * **Phycomycosis (Option B):** Now more commonly referred to as Mucormycosis or Zygomycosis, this is caused by fungi like *Rhizopus* and *Mucor*. It is characterized by angioinvasion and is common in uncontrolled diabetics. * **Actinomycosis (Option C):** This is caused by *Actinomyces israelii*, which is actually a filamentous, anaerobic **Gram-positive bacterium**, not a fungus. It is known for causing "lumpy jaw" and discharging sulfur granules. * **Bleomycosis (Option D):** This is likely a distractor for **Blastomycosis** (Gilchrist's disease). There is no recognized fungal entity called Bleomycosis; Bleomycin is a chemotherapy drug. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Histoplasma* is a **facultative intracellular** fungus. In tissue sections (biopsy), it appears as small, oval yeast cells within **macrophages**. * **Culture:** On Sabouraud Dextrose Agar (SDA) at 25°C, it produces characteristic **tuberculate macroconidia** (thick-walled with finger-like projections). * **Clinical Presentation:** Can cause hepatosplenomegaly, lymphadenopathy, and palatal ulcers in disseminated cases. * **Geography:** While globally distributed, it is classically associated with the Ohio-Mississippi River Valleys in the USA; in India, cases are frequently reported from the Gangetic plains and West Bengal.

Question 390: What is the causative organism in Madura Mycosis?

A. Madurella mycetomatis (Correct Answer)
B. Nocardia
C. Aspergillus
D. Dermatophytes

Explanation: **Explanation:** **Madura Mycosis**, also known as **Eumycetoma**, is a chronic, granulomatous subcutaneous infection characterized by a triad of localized swelling, multiple interconnecting sinus tracts, and the discharge of grains. 1. **Why Madurella mycetomatis is correct:** Mycetoma is classified into two types based on the causative agent: **Eumycetoma** (fungal) and **Actinomycetoma** (bacterial). *Madurella mycetomatis* is the most common fungal cause of Madura Mycosis worldwide. It typically produces **black grains** within the discharge, which are visible to the naked eye and represent compact masses of fungal hyphae. 2. **Why other options are incorrect:** * **Nocardia:** This is a genus of aerobic bacteria that causes **Actinomycetoma**. While the clinical presentation is similar to Madura Mycosis, the treatment differs significantly (antibiotics vs. antifungals). * **Aspergillus:** While *Aspergillus* can cause various infections (aspergilloma, invasive aspergillosis), it is not a primary causative agent of classic Madura Mycosis. * **Dermatophytes:** These fungi cause superficial infections of the skin, hair, and nails (e.g., Tinea). They do not typically cause deep, grain-forming subcutaneous mycetomas. **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** Tumefaction (swelling), Sinus tracts, and Grains. * **Grain Color Clues:** * **Black Grains:** *Madurella mycetomatis*, *Exophiala*. * **White/Pale Grains:** *Pseudallescheria boydii* (Eumycetoma) or *Nocardia* (Actinomycetoma). * **Red Grains:** *Actinomadura pelletieri*. * **Diagnosis:** Histopathology and culture are gold standards. Grains are visualized using KOH mount or Gomori Methenamine Silver (GMS) stain. * **Radiology:** The **"Dot-in-circle" sign** on MRI is highly suggestive of mycetoma.

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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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