Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 411: Tinea pedis is caused by which of the following?

A. E. floccosum (Correct Answer)
B. M. furfur
C. M. canis
D. E. werneckii

Explanation: **Explanation:** **Tinea pedis** (Athlete’s foot) is a dermatophytosis affecting the feet, characterized by scaling, maceration, and itching, most commonly in the interdigital spaces. 1. **Why Option A is Correct:** Dermatophytosis is caused by three genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. **Epidermophyton floccosum** is a common cause of Tinea pedis, Tinea cruris, and Tinea unguium. A key diagnostic feature of *E. floccosum* is that it affects only the **skin and nails**, never the hair. 2. **Why Incorrect Options are Wrong:** * **B. M. furfur (*Malassezia furfur*):** This is a lipophilic yeast responsible for **Pityriasis versicolor** (superficial mycosis), not dermatophytosis. It presents as hypo- or hyperpigmented macules with a "spaghetti and meatballs" appearance on KOH mount. * **C. M. canis (*Microsporum canis*):** While a dermatophyte, it is zoophilic and primarily causes Tinea capitis and Tinea corporis. *Microsporum* species typically affect **hair and skin**, but rarely the nails. * **D. E. werneckii (*Exophiala werneckii*):** This fungus causes **Tinea nigra**, a superficial infection resulting in brown or black painless macules on the palms and soles. **High-Yield Clinical Pearls for NEET-PG:** * **Tissue involvement:** *Trichophyton* (Skin, Hair, Nails), *Microsporum* (Skin, Hair), *Epidermophyton* (Skin, Nails). * **E. floccosum morphology:** Characterized by large, smooth-walled, **club-shaped macroconidia** arranged in pairs or triplets (bananas in a bunch). Microconidia are absent. * **Tinea pedis types:** The "Moccasin type" is most frequently caused by *Trichophyton rubrum*.

Question 412: What is true about mycetoma?

A. Commonly occurs in hands
B. Commonly erodes bone (Correct Answer)
C. Drains through lymphatics
D. Antibiotics have no role

Explanation: **Explanation:** Mycetoma is a chronic, granulomatous, subcutaneous infection characterized by a clinical triad of **localized swelling, multiple interconnecting sinus tracts, and the discharge of grains.** **1. Why Option B is Correct:** Mycetoma is notorious for its local invasiveness. It spreads by contiguity from the skin and subcutaneous tissue to deeper structures. It **commonly erodes bone**, causing characteristic "punched-out" lytic lesions (geodes) and periosteal reactions. Despite extensive bone destruction, the infection is typically painless until late stages. **2. Why Other Options are Incorrect:** * **Option A:** Mycetoma most commonly affects the **lower extremities (foot)**, specifically the dorsal aspect of the forefoot (hence the name "Madura foot"). It is associated with traumatic inoculation (e.g., thorn pricks) in people walking barefoot. * **Option C:** Mycetoma typically spreads locally. **Lymphatic involvement is rare**; if lymphadenopathy occurs, it is usually due to secondary bacterial infection rather than the primary fungus or actinomycete. * **Option D:** Mycetoma is classified into **Actinomycetoma** (caused by filamentous bacteria like *Nocardia*) and **Eumycetoma** (caused by true fungi). **Antibiotics are the mainstay of treatment for Actinomycetoma** (e.g., Welsh regimen using Amikacin and Cotrimoxazole). **Clinical Pearls for NEET-PG:** * **Grains:** The color of the discharge grains provides a diagnostic clue (e.g., Yellow/White in *Nocardia*, Black in *Madurella mycetomatis*). * **Radiology:** The **"Dot-in-circle" sign** on MRI is a pathognomonic feature. * **Eumycetoma** is harder to treat, often requiring long-term antifungals (Itraconazole) and surgical debridement.

Question 413: Which type of hyphae is characteristic of Aspergilloma?

A. Septate hyphae (Correct Answer)
B. Pseudohyphae
C. Metachromatic hyphae
D. No hyphae

Explanation: ### Explanation **Correct Answer: A. Septate hyphae** **1. Why it is correct:** *Aspergillus* species are filamentous fungi characterized by **narrow, septate hyphae** that exhibit **dichotomous branching** (branching into two equal parts) at **acute angles (approximately 45°)**. An Aspergilloma, also known as a "fungus ball," is a saprophytic mass of these fungal hyphae, along with cellular debris and mucus, that typically colonizes pre-existing pulmonary cavities (e.g., old tuberculosis cavities). Under microscopic examination, the structural integrity of the fungus ball is maintained by these distinct septate hyphae. **2. Why the other options are incorrect:** * **B. Pseudohyphae:** These are characteristic of *Candida albicans*. Unlike true hyphae, pseudohyphae are formed by incomplete budding where cells remain attached, showing constrictions at the septa (resembling a string of sausages). * **C. Metachromatic hyphae:** This is not a standard mycological term for fungal morphology. Metachromasia refers to a staining property (e.g., Volutin granules in *C. diphtheriae*) and is not used to describe *Aspergillus* structure. * **D. No hyphae:** This is incorrect because *Aspergillus* is a monomorphic mold; it exists exclusively in the hyphal form in tissue. Yeasts (like *Cryptococcus*) or the yeast phase of dimorphic fungi would show "no hyphae" in certain stages, but not *Aspergillus*. **3. NEET-PG High-Yield Pearls:** * **Radiology:** Aspergilloma presents as a mobile, gravity-dependent mass within a cavity, showing the **"Monod Sign"** or **"Air Crescent Sign"** on Chest X-ray/CT. * **Morphology vs. Mucor:** While *Aspergillus* has narrow, septate hyphae with acute branching (45°), *Mucor/Rhizopus* has wide, **aseptate** hyphae with **right-angle (90°)** branching. * **Culture:** *Aspergillus* grows on Sabouraud Dextrose Agar (SDA), producing smoky green (A. fumigatus), yellowish-green (A. flavus), or black (A. niger) colonies.

Question 414: A KOH wet mount is prepared for identifying which of the following microorganisms?

A. Bacteria
B. Virus
C. Fungus (Correct Answer)
D. Parasite

Explanation: **Explanation:** **1. Why Fungus is Correct:** Potassium Hydroxide (KOH) is the gold standard initial screening tool in mycology. When clinical samples like skin scrapings, hair, or nail clippings are treated with 10–20% KOH, the strong alkali digests the **keratin** and other cellular debris. Since fungal cell walls contain **chitin**, they remain resistant to this digestion. This "clearing" effect allows the fungal elements (hyphae, spores, or budding yeast) to become clearly visible under a light microscope. **2. Why Other Options are Incorrect:** * **Bacteria:** Bacteria are too small to be visualized clearly on a KOH mount and require specific stains like Gram stain or Acid-fast stain to differentiate cell wall structures. * **Virus:** Viruses are sub-microscopic and require electron microscopy or molecular methods (PCR) for identification. * **Parasite:** While some parasites (like *Sarcoptes scabiei*) can be seen on skin scrapings, KOH is specifically used to dissolve proteinaceous material to find fungi. Parasites are typically identified via saline/iodine mounts (stool) or peripheral blood smears. **3. NEET-PG High-Yield Pearls:** * **Modified KOH:** DMSO (Dimethyl sulfoxide) is often added to KOH to speed up the clearing process without requiring heat. * **Calcofluor White:** This is a fluorescent stain often added to KOH mounts; it binds to cellulose and chitin, making fungi fluoresce brilliant blue-white or green. * **Tinea Versicolor:** On KOH mount, *Malassezia furfur* shows a characteristic **"Spaghetti and Meatball"** appearance (short hyphae and globular spores). * **Dermatophytes:** Look for branching, septate hyphae and arthroconidia.

Question 415: Skin scrapings from a patient with tinea corporis were taken and cultured on Sabouraud Dextrose Agar (SDA). A Lactophenol Cotton Blue (LCB) mount shows characteristic macroconidia. What is the likely identity of the causative dermatophyte?

A. Epidermophyton floccosum
B. Microsporum audouinii
C. Microsporum gypseum (Correct Answer)
D. Trichophyton rubrum

Explanation: **Explanation:** The diagnosis of dermatophytosis relies heavily on the morphology of **macroconidia** observed on a Lactophenol Cotton Blue (LCB) mount. **Why Microsporum gypseum is correct:** *Microsporum gypseum* is a geophilic dermatophyte characterized by **abundant, large, thin-walled, symmetrical, ellipsoidal macroconidia**. They typically have rounded ends and contain 4–6 cells. The surface is often slightly echinulate (spiny). In contrast to other species, *M. gypseum* produces these macroconidia in large numbers, making them the dominant feature on microscopy. **Analysis of Incorrect Options:** * **Epidermophyton floccosum:** Characterized by **club-shaped (pyriform)**, smooth, thin-walled macroconidia found in clusters (2–4 cells). Crucially, it **never produces microconidia**. * **Microsporum audouinii:** An anthropophilic species that rarely produces conidia in culture. It is identified by **pectinate (comb-like) hyphae** and terminal chlamydospores. * **Trichophyton rubrum:** The most common cause of tinea corporis worldwide. However, its LCB mount is dominated by **tear-drop shaped microconidia** arranged along the hyphae ("birds on a wire"). Macroconidia are rare, smooth, and pencil-shaped. **High-Yield Clinical Pearls for NEET-PG:** * **Microsporum:** Affects hair and skin; macroconidia are predominant (spindle/fusiform shaped). * **Trichophyton:** Affects hair, skin, and nails; microconidia are predominant. * **Epidermophyton:** Affects skin and nails (NOT hair); only macroconidia are present. * **Wood’s Lamp:** *Microsporum* species (except *M. gypseum*) typically show bright green fluorescence, while *Trichophyton* species generally do not.

Question 416: Infection with Sporothrix schenckii is an occupational hazard for gardeners. What is the typical portal of entry for this organism?

A. Lymphatic system
B. Respiratory tract
C. Skin (Correct Answer)
D. Mouth

Explanation: **Explanation:** **Sporotrichosis**, caused by the dimorphic fungus *Sporothrix schenckii*, is classically known as **"Rose Gardener’s Disease."** 1. **Why Skin is Correct:** The primary portal of entry is the **skin** via **traumatic inoculation**. The fungus resides in soil, moss, and on plant thorns (especially roses). When a gardener or florist sustains a minor puncture wound, the conidia are introduced into the subcutaneous tissue. This leads to a localized nodule that eventually ulcerates. 2. **Why Other Options are Incorrect:** * **Lymphatic System:** While the infection characteristically spreads via the lymphatics (**nodular lymphangitis**), this is the *pathway of spread*, not the *portal of entry*. * **Respiratory Tract:** This is the entry point for systemic dimorphic fungi like *Histoplasma* or *Coccidioides*. Pulmonary sporotrichosis is extremely rare and occurs only via inhalation in immunocompromised states. * **Mouth:** Ingestion is not a recognized route for *Sporothrix* infection. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** It is a **dimorphic fungus**. At 25°C (mould), it shows a "daisy-head" or **rosette appearance** of conidia. At 37°C (yeast), it shows characteristic **cigar-shaped bodies**. * **Clinical Presentation:** Look for the "sporotrichoid spread"—linear nodules along the lymphatic drainage of an extremity. * **Asteroid Bodies:** In tissue sections, yeast cells may be surrounded by eosinophilic radiating processes (Splendore-Hoeppli phenomenon). * **Drug of Choice:** **Itraconazole** is the gold standard. Historically, saturated solution of potassium iodide (SSKI) was used.

Question 417: A black necrotic mass is seen in the nose of an elderly diabetic patient. What is the most probable diagnosis?

A. Lupus vulgaris
B. Aspergillosis
C. Mucormycosis (Correct Answer)
D. Pseudomonas infection

Explanation: ### Explanation **Correct Answer: C. Mucormycosis** **Why it is correct:** The clinical presentation of a **black necrotic mass** (eschar) in the nasal cavity or palate of an **uncontrolled diabetic patient** is a classic hallmark of **Rhinocerebral Mucormycosis**. The underlying mechanism is **angioinvasion**: the fungi (*Rhizopus*, *Mucor*) invade blood vessel walls, leading to thrombosis, tissue ischemia, and subsequent necrosis (hence the black appearance). Hyperglycemia and acidosis (DKA) provide an ideal environment for these fungi to flourish by increasing free iron availability in the blood. **Why the other options are incorrect:** * **Lupus vulgaris:** This is a chronic progressive form of cutaneous tuberculosis. It typically presents as "apple-jelly" nodules on the face, not as an acute necrotic mass in the nose. * **Aspergillosis:** While *Aspergillus* can cause invasive sinusitis, it is more common in neutropenic patients. It rarely presents with the rapid, fulminant black eschar characteristic of Mucormycosis in diabetics. * **Pseudomonas infection:** While it can cause "Ecthyma gangrenosum" (necrotic skin lesions), it is usually seen in septicemic, immunocompromised patients and is not the primary cause of a necrotic nasal mass in a diabetic. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Look for **broad, aseptate hyphae** with **right-angled (90°) branching**. (Contrast with *Aspergillus*: thin, septate hyphae with acute-angled 45° branching). * **Risk Factors:** Diabetes Mellitus (DKA), hematological malignancies, and deferoxamine therapy. * **Treatment:** Immediate surgical debridement and intravenous **Liposomal Amphotericin B**. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as "cotton candy" colonies.

Question 418: A 42-year-old male presented with multiple polyps in the nose. What is the most likely causative agent?

A. Histoplasma
B. Rhinosporidium (Correct Answer)
C. Coccidioides
D. Mucor

Explanation: **Explanation:** The clinical presentation of multiple nasal polyps, particularly in a tropical or rural setting, is a classic hallmark of **Rhinosporidiosis**, caused by ***Rhinosporidium seeberi***. **Why Rhinosporidium is correct:** * **Clinical Presentation:** It typically presents as friable, leafy, or strawberry-like vascular polyps in the nasal cavity, nasopharynx, or conjunctiva. * **Microscopy:** It is characterized by the presence of large, thick-walled **sporangia** (up to 350 µm) filled with thousands of **endospores**. * **Transmission:** It is associated with bathing in stagnant water (ponds/lakes) where the organism resides. Although historically classified as a fungus, it is now considered a **Mesomycetozoean** (a fish parasite). **Why the other options are incorrect:** * **Histoplasma:** Primarily causes pulmonary infections or disseminated disease in immunocompromised patients. While it can cause mucosal ulcers (especially oral), it does not typically present as nasal polyps. * **Coccidioides:** Known for causing "Valley Fever" (respiratory infection) and skin nodules/abscesses, but not primary nasal polyposis. * **Mucor:** Causes **Rhinocerebral Mucormycosis**, an aggressive, invasive infection seen in diabetic or immunocompromised patients. It presents with black necrotic eschars and tissue destruction, rather than chronic polypoid growths. **High-Yield Clinical Pearls for NEET-PG:** * **Stain of choice:** GMS, PAS, and Mucicarmine (stains the sporangial wall). * **Cultivability:** *R. seeberi* **cannot** be cultured on artificial media (Sabouraud Dextrose Agar). * **Treatment:** Surgical excision with wide cautery of the base; Dapsone is sometimes used to prevent recurrence.

Question 419: Non-septate hyphae with a tendency to branch at 90 degree angle is characteristic of which of the following?

A. Mucormycosis (Correct Answer)
B. Aspergillosis
C. Cryptococcus neoformans
D. Coccidioides immitis

Explanation: ### Explanation The correct answer is **Mucormycosis**. #### 1. Why Mucormycosis is Correct Mucormycosis (caused by fungi like *Rhizopus*, *Mucor*, and *Lichtheimia*) is characterized by **broad, ribbon-like, non-septate (coenocytic) hyphae**. A hallmark feature used to differentiate it from other molds is its branching pattern: the hyphae branch at **wide angles (90° or right angles)**. These fungi are angioinvasive, leading to tissue necrosis and black eschar formation, particularly in immunocompromised or diabetic patients. #### 2. Why Other Options are Incorrect * **Aspergillosis:** Characterized by **septate hyphae** that branch at **acute angles (45°)**. This is the most common distractor for this question. * **Cryptococcus neoformans:** This is an **encapsulated yeast**, not a mold. It does not form hyphae; instead, it appears as budding yeast cells with a prominent polysaccharide capsule (visible on India Ink). * **Coccidioides immitis:** This is a dimorphic fungus. In tissue, it forms **spherules filled with endospores**, not branching hyphae. #### 3. High-Yield Clinical Pearls for NEET-PG * **Risk Factors:** Uncontrolled Diabetes Mellitus (especially Ketoacidosis), Neutropenia, and use of Iron chelators (Deferoxamine). * **Clinical Presentation:** Rhinocerebral mucormycosis is the most common form; look for "black eschar" on the palate or nasal turbinates. * **Diagnosis:** KOH mount shows broad non-septate hyphae. Culture on Sabouraud Dextrose Agar (SDA) shows "cotton wool" colonies. * **Treatment:** Liposomal Amphotericin B is the drug of choice; surgical debridement is often necessary. **Mnemonic for Branching:** * **A**spergillus = **A**cute angle (45°) * **M**ucor = **M**ore angle (90°)

Question 420: The chestnut coloured fungal cells known as muriform bodies are seen in which of the following conditions?

A. Sporotrichosis
B. Phaeohyphomycosis
C. Chromoblastomycosis (Correct Answer)
D. Lobomyomycosis

Explanation: ### Explanation **Correct Answer: C. Chromoblastomycosis** **Chromoblastomycosis** is a chronic subcutaneous mycosis caused by dematiaceous (pigmented) fungi, most commonly *Fonsecaea pedrosoi*. The hallmark pathological feature of this condition is the presence of **Muriform bodies** (also known as **Medlar bodies**, **Sclerotic bodies**, or **Copper-penny bodies**). These are thick-walled, dark brown (chestnut-colored) fungal cells that divide by binary fission (septation) rather than budding. Their presence in skin scrapings (KOH mount) or histopathology is pathognomonic for Chromoblastomycosis. Clinically, it presents as slow-growing, "cauliflower-like" verrucous lesions, typically on the lower limbs of individuals working barefoot. --- ### Why other options are incorrect: * **A. Sporotrichosis:** Caused by *Sporothrix schenckii*. The characteristic histological finding is the **Asteroid body** (an eosinophilic radiating substance surrounding a yeast cell) or cigar-shaped yeast cells. * **B. Phaeohyphomycosis:** While also caused by dematiaceous fungi, it is characterized by the presence of **pigmented hyphae** and yeast-like cells in tissue, but it **never** forms muriform bodies. * **C. Lobomycosis:** Caused by *Lacazia loboi*. It is characterized by yeast cells arranged in a **"string of beads"** or "lemon-shaped" chains. --- ### High-Yield Clinical Pearls for NEET-PG: * **Muriform bodies** are diagnostic; they represent a transitional form between yeast and hyphae. * **Copper-penny appearance** is due to the presence of **melanin** in the fungal cell wall. * **Treatment of choice:** Itraconazole or Terbinafine; surgical excision is used for small lesions. * **Differential Diagnosis:** Often confused with Squamous Cell Carcinoma (SCC) due to the verrucous appearance and pseudoepitheliomatous hyperplasia on biopsy.

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Classification of Fungi

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Superficial 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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Mycology — MCQs

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