Mycology Practice Questions

Q: 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?

Microsporum gypseum. **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.

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

Mucormycosis. ### 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.

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

Rhinosporidium. **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.

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

Mucormycosis. ### 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°)

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

Chromoblastomycosis. ### 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.

Q: Which of the following fungi has not been cultured?

Rhinosporidium. **Explanation:** The correct answer is **Rhinosporidium seeberi**. Despite its name and historical classification as a fungus, *Rhinosporidium seeberi* has **never been successfully cultured** on artificial laboratory media or in cell culture. 1. **Why Rhinosporidium is correct:** Recent molecular phylogenetic analysis (18S rRNA sequencing) has reclassified this organism as a **Mesomycetozoean**, a group of aquatic protists (parasites) located at the evolutionary boundary between animals and fungi. It causes **Rhinosporidiosis**, characterized by friable, leafy, strawberry-like vascular polyps in the nose or conjunctiva. Diagnosis relies entirely on microscopy (histopathology) showing large, thick-walled **sporangia** containing thousands of **endospores**. 2. **Why other options are incorrect:** * **Sporothrix schenckii:** A dimorphic fungus that is easily cultured. At 25°C, it grows as a mold with characteristic "flower-like" or "daisy-head" conidia. * **Acremonium:** A filamentous fungus (hyphomycete) known for causing eumycetoma. It grows well on Sabouraud Dextrose Agar (SDA), producing fine, septate hyphae. * **Blastomyces dermatitidis:** A systemic dimorphic fungus that can be cultured on SDA. It shows a "lolipop" appearance of conidia at room temperature and yeast forms at 37°C. **High-Yield NEET-PG Pearls:** * **Habitat:** *Rhinosporidium* is associated with stagnant water and is most common in South India (Tamil Nadu, Kerala) and Sri Lanka. * **Stains:** Sporangia are easily visualized with H&E, GMS, and PAS stains. * **Treatment:** Surgical excision with electrocautery is the treatment of choice; medical therapy (Dapsone) has limited efficacy. * **Other "Unculturables":** Remember that *Lacazia loboi* (Lobomycosis) and *Pneumocystis jirovecii* (difficult/non-routine) are other organisms often discussed in this context.

Q: Tinea versicolor is typically associated with which organism?

Pityrosporum orbiculare. **Explanation:** **Tinea versicolor** (also known as Pityriasis versicolor) is a common superficial fungal infection caused by the overgrowth of **Malassezia furfur**, a lipophilic yeast. Historically, the round yeast forms found on the skin were named ***Pityrosporum orbiculare***, while the oval forms were called *Pityrosporum ovale*. Therefore, *Pityrosporum orbiculare* is the correct mycological designation for the causative agent in this context. **Analysis of Incorrect Options:** * **B. Candida infection:** Causes Candidiasis, typically presenting as erythematous plaques with characteristic "satellite lesions" in intertriginous areas (e.g., diaper dermatitis, intertrigo), not the scaly hypo/hyperpigmented macules of Tinea versicolor. * **C. Epidermophyton:** This is a genus of dermatophytes (e.g., *E. floccosum*) that causes infections like Tinea cruris and Tinea pedis. Unlike Malassezia, dermatophytes invade keratinized tissue. * **D. Trichophyton:** The most common genus of dermatophytes (e.g., *T. rubrum*). It is responsible for most cases of Tinea corporis, Tinea capitis, and onychomycosis. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** KOH mount shows the classic **"Spaghetti and Meatballs"** appearance (short, blunt hyphae and thick-walled budding spores). * **Wood’s Lamp:** Lesions emit a characteristic **yellowish-gold or pale orange fluorescence**. * **Clinical Sign:** **Selisky’s Sign** (Evoked Scale) – scraping the lesion produces fine, branny scales (furfuraceous). * **Treatment:** Topical antifungals like Ketoconazole or Selenium sulfide are first-line. Oral Fluconazole is used for extensive cases.

Q: Cryptococcal meningitis is common in which patient population?

Renal transplant recipients. **Explanation:** **Cryptococcus neoformans** is an opportunistic encapsulated yeast that primarily causes infection in patients with **impaired cell-mediated immunity (CMI)**. 1. **Why Option A is Correct:** Renal transplant recipients are maintained on long-term immunosuppressive therapy (such as corticosteroids, calcineurin inhibitors like tacrolimus, and mycophenolate mofetil) to prevent graft rejection. These drugs specifically suppress **T-cell function**. Since CMI is the primary defense mechanism against *Cryptococcus*, these patients are at high risk for disseminated cryptococcosis and meningitis. 2. **Why Other Options are Incorrect:** * **Options B & D (Gamma globulinemia/IgA deficiency):** These represent humoral (B-cell) immunity defects. While antibodies play a role, they are not the primary defense against fungal pathogens like *Cryptococcus*. * **Option C (Neutropenia):** Neutrophils are the primary defense against molds (like *Aspergillus*) and *Candida*. Cryptococcal risk is more closely linked to T-cell deficits (e.g., HIV/AIDS, transplants) rather than absolute neutrophil count. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** *Cryptococcus* is the most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100 cells/µL). * **Diagnosis:** * **India Ink:** Shows a wide, clear, non-staining polysaccharide capsule (negative staining). * **Latex Agglutination:** Detects cryptococcal capsular antigen (highly sensitive and specific). * **Culture:** Sabouraud Dextrose Agar (SDA) produces creamy, mucoid colonies. * **Biopsy:** Mucicarmine stain specifically highlights the capsule in red. * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by maintenance with Fluconazole.

Q: A diabetic patient with orbital cellulitis and maxillary sinusitis shows hyaline, narrow, septate, and branching hyphae with invasion of blood vessels on microscopy. Which is the causative fungus?

Aspergillus. **Explanation:** The clinical presentation of orbital cellulitis and sinusitis in a diabetic patient, combined with the specific microscopic findings, points directly to **Aspergillus**. **1. Why Aspergillus is correct:** The hallmark of *Aspergillus* species in tissue sections is the presence of **hyaline (clear), narrow, septate hyphae** that exhibit **dichotomous branching at acute angles (approximately 45°)**. Like Mucormycosis, Aspergillus is **angioinvasive**, meaning it invades blood vessel walls, leading to thrombosis and tissue infarction, which explains the aggressive clinical presentation in this patient. **2. Why other options are incorrect:** * **Rhizopus (Mucormycosis):** While it also causes aggressive rhino-orbital-cerebral disease in diabetics, its morphology is distinct: it features **broad, aseptate (coenocytic) hyphae** with **right-angle (90°) branching**. * **Candida:** Typically appears as budding yeast cells and **pseudohyphae** (elongated buds with constrictions). It does not usually present as a primary invasive fungal sinusitis with branching septate hyphae. * **Histoplasma:** This is a dimorphic fungus that, in tissue, appears as small (2-4 µm) **intracellular yeast cells** within macrophages, not as invasive branching hyphae. **High-Yield NEET-PG Pearls:** * **Acute Angle (45°) + Septate:** Aspergillus. * **Right Angle (90°) + Aseptate:** Rhizopus/Mucor. * **Vessel Invasion:** Both Aspergillus and Rhizopus are angioinvasive, but the septation and branching angle are the key differentiating factors. * **Culture:** Aspergillus grows on Sabouraud Dextrose Agar (SDA) and produces characteristic "conidial heads." *Aspergillus fumigatus* is the most common species involved in invasive disease.

Question 1

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?

Accepted Answer

Microsporum gypseum

Answer

Epidermophyton floccosum

Answer

Microsporum audouinii

Answer

Trichophyton rubrum

Question 2

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

Accepted Answer

Mucormycosis

Answer

Lupus vulgaris

Answer

Aspergillosis

Answer

Pseudomonas infection

Question 3

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

Accepted Answer

Rhinosporidium

Answer

Histoplasma

Answer

Coccidioides

Answer

Mucor

Question 4

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

Accepted Answer

Mucormycosis

Answer

Aspergillosis

Answer

Cryptococcus neoformans

Answer

Coccidioides immitis

Question 5

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

Accepted Answer

Chromoblastomycosis

Answer

Sporotrichosis

Answer

Phaeohyphomycosis

Answer

Lobomyomycosis

Question 6

Mycetoma is caused by which of the following agents?

Accepted Answer

Trichosporum beigelli

Answer

Allescheria boydii

Answer

Madurella mycetomii

Answer

Nocardia asteroides

Question 7

Which of the following fungi has not been cultured?

Accepted Answer

Rhinosporidium

Answer

Sporothrix

Answer

Acremonium

Answer

Blastomyces

Question 8

Tinea versicolor is typically associated with which organism?

Accepted Answer

Pityrosporum orbiculare

Answer

Candida infection

Answer

Epidermophyton

Answer

Trichophyton

Question 9

Cryptococcal meningitis is common in which patient population?

Accepted Answer

Renal transplant recipients

Answer

Patients with gamma globulinemia

Answer

Patients with neutropenia

Answer

Patients with IgA deficiency

Question 10

A diabetic patient with orbital cellulitis and maxillary sinusitis shows hyaline, narrow, septate, and branching hyphae with invasion of blood vessels on microscopy. Which is the causative fungus?

Accepted Answer

Aspergillus

Answer

Candida

Answer

Rhizopus

Answer

Histoplasma

Mycology — MCQs

Mycology — MCQs

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