Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 11: What is the primary mechanism by which most fungi cause disease?

A. Exotoxin production
B. Lecithinase production
C. Hypersensitivity (Correct Answer)
D. Coagulase production

Explanation: ### Explanation The primary mechanism of fungal pathogenicity differs significantly from bacteria. Most fungi are **accidental pathogens** with low virulence; they cause disease primarily through the host's immune response rather than through specific aggressive virulence factors. **1. Why Hypersensitivity is Correct:** Fungi are highly antigenic. Most human fungal diseases are the result of **Hypersensitivity (Type I, III, or IV)** to fungal spores or metabolic products. For example, **Allergic Bronchopulmonary Aspergillosis (ABPA)** is a classic hypersensitivity reaction. While some fungi cause direct tissue invasion (especially in immunocompromised hosts), the broad spectrum of fungal diseases—ranging from superficial dermatophytosis to systemic allergies—is dominated by the host's inflammatory and allergic response. **2. Why Other Options are Incorrect:** * **Exotoxin production (A):** Unlike bacteria (e.g., *C. tetani*), fungi rarely produce classic exotoxins to cause systemic disease. While some produce **mycotoxins** (like Aflatoxin), these are usually ingested (mycotoxicosis) rather than secreted during an active infection to cause disease. * **Lecithinase (B):** This is a characteristic alpha-toxin produced by ***Clostridium perfringens*** to cause gas gangrene, not a primary fungal mechanism. * **Coagulase (C):** This enzyme is the hallmark of ***Staphylococcus aureus***, used to convert fibrinogen to fibrin; it is not a mechanism used by fungi. **NEET-PG High-Yield Pearls:** * **Most common fungal infection:** Candidiasis (Opportunistic). * **Major defense against fungi:** Cell-Mediated Immunity (T-cells). Neutrophils are primary against *Candida* and *Aspergillus*. * **Aflatoxin:** Produced by *Aspergillus flavus*; associated with **Hepatocellular Carcinoma**. * **Ergotism:** Caused by *Claviceps purpuea* (St. Anthony’s Fire).

Question 12: What is commonly known as the golden yellow jelly fungus?

A. Ttursurans
B. Tmontegrophytes
C. Tremella mesenterica (Correct Answer)
D. Efloccosum

Explanation: **Explanation:** **Tremella mesenterica** (Option C) is the correct answer. It is a common basidiomycete fungus frequently referred to as the **"Golden Yellow Jelly Fungus,"** "Yellow Brain," or "Witch's Butter." It is characterized by its gelatinous, lobed, and bright yellow-to-orange fruiting body. In medical mycology and microbiology, it is often studied as a model organism for dimorphism and its unique polysaccharide composition (glucuronoxylomannan), which shares structural similarities with the capsule of *Cryptococcus neoformans*. **Analysis of Incorrect Options:** * **A. T. tonsurans (Trichophyton tonsurans):** An anthropophilic dermatophyte. It is the leading cause of *Tinea capitis* (endothrix infection) and is known for causing "black dot" ringworm, not a jelly-like appearance. * **B. T. mentagrophytes (Trichophyton mentagrophytes):** A zoophilic/anthropophilic dermatophyte that causes inflammatory skin and nail infections. It is characterized by spiral hyphae and cigar-shaped macroconidia on microscopy. * **D. E. floccosum (Epidermophyton floccosum):** A dermatophyte that affects skin and nails (never hair). It is identified by its characteristic club-shaped, smooth-walled macroconidia arranged in clusters (beaver-tail appearance). **High-Yield Clinical Pearls for NEET-PG:** * **Cryptococcus connection:** *Tremella* species are taxonomically related to *Cryptococcus*. Both belong to the class Tremellomycetes. * **Dermatophyte Distinction:** Remember that *Epidermophyton* does **not** infect hair, whereas *Trichophyton* infects skin, hair, and nails. * **T. tonsurans:** Look for "Endothrix" (spores inside the hair shaft) and "Black dot" alopecia in clinical vignettes.

Question 13: Which organism is known as the 'sun ray fungus'?

A. Actinomyces israelii (Correct Answer)
B. Chromoblastomycosis
C. Streptomyces griseus
D. Cryptococcus

Explanation: **Explanation:** The term **'Sun ray fungus'** refers to **Actinomyces israelii**. This name is derived from the characteristic microscopic appearance of the organism in tissue sections (sulfur granules). When stained and viewed under a microscope, these granules consist of a central mass of tangled filaments with peripheral, radiating, club-shaped structures, resembling the rays of the sun. **Why the other options are incorrect:** * **Chromoblastomycosis:** This is a chronic fungal infection characterized by "sclerotic bodies" (copper penny bodies/Medlar bodies), not a sun-ray appearance. * **Streptomyces griseus:** While it is an actinomycete and shares some morphological similarities, it is primarily known as a source of the antibiotic Streptomycin rather than for the "sun ray" clinical description. * **Cryptococcus:** This is an encapsulated yeast known for its thick polysaccharide capsule, visualized using India Ink. It typically presents as budding yeast cells, not radiating filaments. **High-Yield Clinical Pearls for NEET-PG:** * **Nature of Organism:** Despite the name ending in "-myces," *Actinomyces* is a **Gram-positive anaerobic bacterium**, not a true fungus. * **Sulfur Granules:** These are pathognomonic macroscopic yellow specks found in pus from lesions. * **Clinical Presentation:** Most commonly causes **Cervicofacial actinomycosis** ("Lumpy Jaw") following dental trauma or poor oral hygiene. * **Microscopy:** Gram stain shows Gram-positive branching filaments. * **Treatment:** The drug of choice is **Penicillin G** (long-term). Remember the mnemonic: *"Actinomyces likes the AC"* (Actinomyces = Penicillin/Amoxicillin).

Question 14: San Joaquin Valley fever is caused by which organism?

A. B. dermatitidis
B. Cryptococcus neoformans
C. Coccidioides immitis (Correct Answer)
D. H. capsulatum

Explanation: **Explanation:** **Coccidioides immitis** is the causative agent of **Coccidioidomycosis**, also known as **San Joaquin Valley fever** (or simply Valley fever). This fungal infection is endemic to the arid regions of the Southwestern United States (specifically the San Joaquin Valley in California) and Northern Mexico. It is a dimorphic fungus that exists as mold in the soil and transforms into **spherules containing endospores** within the host lungs. **Analysis of Options:** * **B. dermatitidis (Blastomycosis):** Known as "North American Blastomycosis" or "Gilchrist’s disease." It is endemic to the Ohio and Mississippi River valleys and is characterized by "Broad-Based Budding" yeast. * **Cryptococcus neoformans:** An opportunistic encapsulated yeast (not dimorphic) commonly associated with pigeon droppings. It is a leading cause of fungal meningitis in HIV/AIDS patients. * **H. capsulatum (Histoplasmosis):** Known as "Darling’s disease" or "Ohio Valley Fever." It is associated with bird or bat droppings (guano) and is characterized by small intracellular yeasts within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Coccidioides* is unique among dimorphic fungi; it forms **spherules** in tissue, not yeast. * **Transmission:** Inhalation of **arthroconidia** (infectious spores) from disturbed soil or during dust storms. * **Clinical Presentation:** Ranges from a self-limiting flu-like illness to severe pneumonia. A classic triad includes fever, joint pain (Desert Rheumatism), and **Erythema Nodosum**. * **Diagnosis:** Identification of thick-walled spherules filled with endospores on KOH mount or biopsy. Culture on Sabouraud Dextrose Agar (SDA) shows highly infectious arthroconidia.

Question 15: A farmer from the sub-Himalayan region presents with multiple leg ulcers. What is the most likely causative agent?

A. Trichophyton Rubrum
B. Cladosporium species
C. Sporothrix Schenckii (Correct Answer)
D. Aspergillus

Explanation: **Explanation:** The clinical presentation of a farmer with multiple leg ulcers, particularly in the sub-Himalayan region, is a classic description of **Sporotrichosis**, caused by the dimorphic fungus **_Sporothrix schenckii_**. **Why Sporothrix schenckii is correct:** * **Occupational Hazard:** It is known as "Rose Gardener’s Disease" because the fungus resides in soil, moss, and decaying vegetation. Farmers and gardeners are at high risk due to traumatic inoculation (e.g., thorn pricks). * **Geographic Link:** In India, the sub-Himalayan belt (including Himachal Pradesh and West Bengal) is a known endemic zone. * **Clinical Pattern:** It typically presents as a primary nodule at the site of inoculation which ulcerates, followed by the development of secondary nodules along the path of lymphatic drainage (**Lymphocutaneous sporotrichosis**). **Analysis of Incorrect Options:** * **A. Trichophyton rubrum:** A common dermatophyte causing superficial infections like Tinea pedis or corporis. It presents as itchy, scaly annular plaques, not deep ulcers. * **B. Cladosporium species:** These are common causes of Chromoblastomycosis. While they cause chronic skin lesions, they typically present as "cauliflower-like" verrucous (warty) growths rather than simple ulcers. * **D. Aspergillus:** Primarily causes opportunistic pulmonary infections or allergic manifestations. While cutaneous aspergillosis exists, it is rare and usually seen in severely immunocompromised patients, not as a primary occupational ulcer in farmers. **NEET-PG High-Yield Pearls:** * **Morphology:** It is a **dimorphic fungus**. At 25°C (mold), it shows "flower-like" or **daisy-head** conidia. At 37°C (yeast), it shows **cigar-shaped** bodies. * **Histology:** Look for **Asteroid bodies** (Splendore-Hoeppli phenomenon). * **Drug of Choice:** **Itraconazole** is the preferred treatment. Saturated Solution of Potassium Iodide (SSKI) was historically used.

Question 16: Which phylum do medically important fungi belong to?

A. Deuteromycota (Correct Answer)
B. Basidiomycota
C. Ascomycota
D. Zygomycota

Explanation: ### Explanation **Correct Answer: A. Deuteromycota** In medical mycology, fungi are classified based on their method of sexual reproduction. **Deuteromycota**, also known as "Fungi Imperfecti," is the phylum that contains the vast majority of medically important fungi. These fungi are grouped here because their **sexual stage (teleomorph) is either absent, unknown, or has not been observed**. Since most human fungal pathogens primarily exist and are identified in their asexual state (anamorph) in clinical specimens, they are traditionally categorized under this phylum. Examples include *Candida*, *Aspergillus*, and the Dermatophytes. **Analysis of Incorrect Options:** * **B. Basidiomycota:** These are "club fungi" that produce sexual spores (basidiospores) on a basidium. While most are mushrooms, the medically significant exception is *Cryptococcus neoformans*. * **C. Ascomycota:** Known as "sac fungi," they produce sexual spores (ascospores) within an ascus. Some fungi (like *Histoplasma*) have an ascomycetous teleomorph but are still clinically discussed alongside Deuteromycetes. * **D. Zygomycota:** These produce thick-walled sexual zygospores. This phylum includes the orders Mucorales (e.g., *Rhizopus*, *Mucor*), known for causing rhinocerebral mucormycosis in diabetic patients. **High-Yield Clinical Pearls for NEET-PG:** * **Taxonomic Shift:** Modern molecular phylogenetics is phasing out the name "Deuteromycota" as sexual stages are discovered, but it remains the standard answer for "Fungi Imperfecti" in exams. * **Dimorphic Fungi:** Most systemic mycoses (e.g., *Histoplasma*, *Blastomyces*) are dimorphic—existing as molds in the environment (25°C) and yeasts in human tissue (37°C). * **Cell Wall Marker:** Fungal cell walls contain **Chitin** and **Beta-glucan**, which are targets for antifungals like Echinocandins.

Question 17: Which fungus causes hair, skin, and nail infections?

A. T. rubrum (Correct Answer)
B. E. floculossum
C. M. Canis
D. M. Ayouni

Explanation: ### Explanation The question tests the classification of **Dermatophytes**, a group of fungi that require keratin for growth and cause superficial infections (Tinea). Dermatophytes are categorized into three genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. **1. Why Trichophyton rubrum is correct:** *Trichophyton* species are unique because they have the capacity to infect all three keratinized tissues: **Hair, Skin, and Nails**. *T. rubrum* is the most common cause of dermatophytosis worldwide, frequently causing Tinea pedis, Tinea cruris, and Onychomycosis (nail infection). **2. Analysis of Incorrect Options:** * **B. Epidermophyton floccosum:** This genus infects only **Skin and Nails**. It notably **never infects hair**. * **C. Microsporum canis:** This genus infects **Hair and Skin**. It typically **does not infect nails**. * **D. M. audouinii (M. Ayouni):** Similar to other *Microsporum* species, it primarily affects hair (causing Tinea capitis) and skin, but spares the nails. **3. High-Yield Clinical Pearls for NEET-PG:** * **The Rule of Three:** * *Trichophyton*: Hair, Skin, Nails (All 3) * *Microsporum*: Hair, Skin (No Nails) * *Epidermophyton*: Skin, Nails (No Hair) * **T. rubrum Identification:** On Sabouraud Dextrose Agar (SDA), it produces a characteristic **cherry-red/blood-red reverse pigment**. * **Microscopic feature:** *Trichophyton* is characterized by abundant microconidia and rare, pencil-shaped macroconidia. * **Wood’s Lamp:** *Microsporum* species (like *M. canis*) show bright green fluorescence, whereas *Trichophyton* species (except *T. schoenleinii*) generally do not fluoresce.

Question 18: Gram stained periorbital exudates in severe panophthalmitis with cellulitis in an elderly diabetic shows irregular branching aseptate and broad hyphae. Which of the following is the most likely diagnosis?

A. Candida
B. Aspergillus
C. Pencillium
D. Apophysomyces species (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Apophysomyces species** The clinical presentation of severe panophthalmitis and cellulitis in an elderly diabetic patient, combined with the specific microscopic findings, points directly to **Mucormycosis**. **Why Apophysomyces is correct:** * **Microscopic Morphology:** The description of **"irregular branching, aseptate (coenocytic), and broad hyphae"** is the classic hallmark of the order Mucorales. * **Clinical Context:** Diabetics are highly predisposed to Rhino-oculo-cerebral mucormycosis (ROCM). * **Genus Identification:** While *Rhizopus* is the most common cause globally, *Apophysomyces elegans* is a significant cause of invasive mucormycosis in India, often following trauma or in immunocompromised states. Among the given options, it is the only member of the Mucorales family. **Why other options are incorrect:** * **A. Candida:** Shows budding yeast cells and **pseudohyphae** (constrictions at septa), not broad aseptate hyphae. * **B. Aspergillus:** Characterized by **septate** hyphae with regular, **dichotomous branching at acute angles** (45°). * **C. Penicillium:** Also features septate hyphae and characteristic "brush-like" conidiophores (Penicillus) in culture; it does not match the "broad aseptate" description. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** Mucorales are best visualized with **KOH mount** or silver stains (GMS/PAS). They often stain weakly on Gram stain but appear as "ghost-like" broad outlines. * **Risk Factors:** Diabetic Ketoacidosis (DKA) is the classic association because Mucorales thrive in acidic, iron-rich environments (using siderophores). * **Treatment:** The drug of choice is **Liposomal Amphotericin B**, along with aggressive surgical debridement. * **Key Distinction:** * *Mucor/Rhizopus:* Aseptate, wide-angle (90°) branching. * *Aspergillus:* Septate, acute-angle (45°) branching.

Question 19: Maltese cross formation is observed on polarizing microscopy in which of the following?

A. Cryptococcus neoformans (Correct Answer)
B. Penicillium marneffei
C. Plasmodium falciparum
D. Candida albicans

Explanation: **Explanation:** The correct answer is **Cryptococcus neoformans**. **Why it is correct:** *Cryptococcus neoformans* is an encapsulated yeast. When clinical specimens (such as CSF or tissue sections) or cultures are viewed under **polarizing microscopy**, the thick polysaccharide capsule exhibits **birefringence**. This optical property results in the characteristic **"Maltese cross"** appearance (a cross-shaped light pattern). This is a high-yield diagnostic feature used to identify the fungus in histopathological sections, especially when stained with Gomori Methenamine Silver (GMS) or PAS. **Analysis of Incorrect Options:** * **Penicillium marneffei (Talaromyces marneffei):** This is a dimorphic fungus characterized by intracellular yeast cells with a central transverse septum (fission). It does not show a Maltese cross. * **Plasmodium falciparum:** This is a protozoan parasite. While it produces hemozoin pigment, it does not exhibit the Maltese cross pattern. (Note: *Babesia* species show a "Maltese cross" arrangement of four merozoites in RBCs, but this is a structural arrangement, not a polarizing microscopy finding). * **Candida albicans:** This yeast typically shows budding cells and pseudohyphae. Its cell wall does not produce a birefringent Maltese cross under polarization. **NEET-PG High-Yield Pearls:** 1. **Maltese Cross in Microbiology:** Seen in *Cryptococcus* (polarizing microscopy) and *Babesia* (tetrad arrangement on Giemsa stain). 2. **Maltese Cross in Pathology:** Seen in **Urinary lipids** (nephrotic syndrome), **Starch granules** (contaminants), and **Ethyl glycol poisoning** (calcium oxalate crystals). 3. **Cryptococcus Stains:** India Ink (negative staining for capsule), Mucicarmine (bright red capsule), and Fontana-Masson (detects melanin in the cell wall). 4. **Virulence Factor:** The polysaccharide capsule (GXM) is the primary virulence factor, inhibiting phagocytosis.

Question 20: Fungal spores may be produced in which of the following ways?

A. Singly
B. In chains
C. In sporangium
D. All of the above (Correct Answer)

Explanation: ### Explanation Fungi reproduce primarily through the formation of **spores**, which can be sexual or asexual. The morphology and arrangement of these spores are key diagnostic features in medical mycology. **Why "All of the above" is correct:** Fungi exhibit diverse mechanisms for spore production depending on the species and environmental conditions: * **Singly:** Some fungi produce solitary spores. For example, **Blastomyces** produces single terminal conidia (the "lollipop" appearance). * **In chains:** Many fungi, most notably **Aspergillus** and **Penicillium**, produce conidia in long, linear chains (catenulate) from specialized structures called phialides. * **In sporangium:** Members of the order Mucorales (e.g., **Rhizopus, Mucor**) produce asexual spores (sporangiospores) within a sac-like structure called a **sporangium**. When the sporangial wall ruptures, the spores are released. **Analysis of Options:** * **Option A, B, and C** are all correct but incomplete on their own. Since fungi utilize all three methods for dissemination and survival, "All of the above" is the most accurate choice. **High-Yield Clinical Pearls for NEET-PG:** * **Asexual Spores:** These include Conidia (formed on conidiophores) and Sporangiospores (formed within a sporangium). * **Sexual Spores:** Remember the mnemonic **BASE**—**B**asidiospores, **A**scospores, **S**ygospores (Zygospores), and **E**ospores (Oospores). * **Arthrospores:** Formed by fragmentation of hyphae (e.g., *Coccidioides immitis*, *Dermatophytes*). * **Chlamydospores:** Thick-walled resting spores (e.g., *Candida albicans* produces terminal chlamydospores on Cornmeal Agar).

Practice by Chapter

Classification of Fungi

Practice Questions

Superficial Mycoses

Practice Questions

Dermatophytes

Practice Questions

Subcutaneous Mycoses

Practice Questions

Candidiasis

Practice Questions

Aspergillosis

Practice Questions

Cryptococcosis

Practice Questions

Zygomycosis

Practice Questions

Endemic Mycoses

Practice Questions

Opportunistic Fungal Infections

Practice Questions

Antifungal Agents

Practice Questions

Laboratory Diagnosis of Fungal Infections

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free

Mycology — MCQs

Mycology — MCQs

On this page

Practice by Chapter

Want unlimited practice?