Mycology Practice Questions

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.

Q: A 63-year-old man with insulin-dependent diabetes develops a black, crusting lesion in the nose and left maxillary sinus. Biopsy reveals nonseptate hyphae. What is the diagnosis?

Mucor mycosis. **Explanation:** The clinical presentation of a **black, crusting lesion** (eschar) in the nasal cavity and maxillary sinus of an **uncontrolled diabetic patient** is a classic hallmark of **Rhinocerebral Mucormycosis**. **Why Mucormycosis is correct:** Mucormycosis is an opportunistic fungal infection caused by fungi of the order Mucorales. It predominantly affects immunocompromised individuals, especially those with **Diabetic Ketoacidosis (DKA)** or poorly controlled diabetes. The fungus thrives in acidic, glucose-rich environments. The definitive histopathological finding is the presence of **broad, non-septate hyphae** that branch at **right angles (90°)**. These fungi are angioinvasive, leading to tissue infarction and the characteristic black necrotic eschar. **Why other options are incorrect:** * **Erysipelas:** A superficial bacterial skin infection (usually *S. pyogenes*) characterized by a well-demarcated, raised, erythematous rash. It does not present with non-septate hyphae or deep sinus involvement. * **Eczema:** An inflammatory skin condition (atopic dermatitis) presenting with pruritus and vesicles; it is not an invasive fungal infection. * **Scarlet fever:** A systemic bacterial infection caused by Group A Streptococcus, characterized by a "sandpaper" rash and "strawberry tongue," not necrotic sinus lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factor:** Uncontrolled Diabetes (DKA) is the most common association. * **Microscopy:** Broad, ribbon-like, **non-septate** hyphae with **90-degree (right-angle)** branching. (Contrast with *Aspergillus*: Septate hyphae with 45-degree branching). * **Treatment:** Immediate surgical debridement + Intravenous **Liposomal Amphotericin B**. * **Complication:** Can spread rapidly to the orbit (proptosis) and brain (cavernous sinus thrombosis).

Q: Which of the following represents a dimorphic fungus causing subcutaneous mycosis?

Sporotrichosis. **Explanation:** The correct answer is **Sporotrichosis** (*Sporothrix schenckii*). To answer this question correctly, one must distinguish between the classification of fungi based on the **site of infection** and their **morphological characteristics**. **1. Why Sporotrichosis is correct:** * **Classification:** It is the classic example of a **subcutaneous mycosis**. * **Dimorphism:** It is a **thermally dimorphic** fungus. At room temperature (25°C), it exists in a mold form (septate hyphae with "rosette-like" conidia), and at body temperature (37°C), it exists as a pleomorphic yeast (often described as **cigar-shaped bodies**). * **Clinical Context:** It typically follows traumatic inoculation (e.g., a thorn prick), leading to "Rose Gardener’s Disease," characterized by linear nodules along lymphatic channels (lymphocutaneous spread). **2. Why other options are incorrect:** * **Histoplasmosis (A) & Blastomycosis (D):** While both are thermally dimorphic, they are classified as **Systemic Mycoses**. They primarily cause pulmonary infections via inhalation of spores rather than subcutaneous infections via inoculation. * **Rhinosporidiosis (B):** Caused by *Rhinosporidium seeberi*, it affects mucous membranes (nose/eyes) and is classified as a subcutaneous mycosis. However, it is **not dimorphic**; it is currently classified as a Mesomycetozoea (a protist-like parasite) and produces characteristic sporangia containing endospores. **NEET-PG High-Yield Pearls:** * **Asteroid Bodies:** Often seen in sporotrichosis (Splendore-Hoeppli phenomenon). * **Drug of Choice:** Oral **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. * **Culture:** On Sabouraud Dextrose Agar (SDA), *Sporothrix* produces moist, wrinkled colonies that turn black over time.

Q: Pneumocystis carinii typically infects which host?

Rat. **Explanation:** The nomenclature of *Pneumocystis* species has undergone significant revision based on genetic analysis. The organism originally named ***Pneumocystis carinii*** is now recognized as a species that specifically infects **rats**. The species that causes human infection (Pneumocystis pneumonia or PCP) is now formally named ***Pneumocystis jirovecii***. This distinction is critical for NEET-PG, as the organism exhibits strict **host-species specificity**, meaning the species infecting one animal cannot infect another. **Analysis of Options:** * **C. Rat (Correct):** *P. carinii* is the specific name reserved for the strain found in rats. It was the first species described and was long used as a blanket term for all *Pneumocystis* infections before DNA sequencing proved host specificity. * **A. Human:** Humans are infected by ***P. jirovecii***. While older textbooks may use the term *P. carinii* interchangeably, modern medical exams differentiate them. * **B. Monkey:** Monkeys are infected by *P. oryctolagi* or other host-specific strains, not *P. carinii*. * **D. Cats:** Similarly, cats have their own specific strains of *Pneumocystis*. **High-Yield Clinical Pearls for NEET-PG:** * **Taxonomy:** Formerly classified as a protozoan, *Pneumocystis* is now classified as a **fungus** based on nucleic acid analysis (rRNA). * **Staining:** The gold standard for diagnosis is the **Gomori Methenamine Silver (GMS)** stain, which reveals "crushed ping-pong ball" or "cup-shaped" cysts. * **Clinical Marker:** Elevated **Beta-D-Glucan** levels in the serum are a sensitive (though non-specific) marker for PCP. * **Treatment:** The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, not traditional antifungals like Amphotericin B, because *Pneumocystis* lacks ergosterol in its cell membrane.

Question 1

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 2

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 3

Mycetoma is caused by which of the following agents?

Accepted Answer

Trichosporum beigelli

Answer

Allescheria boydii

Answer

Madurella mycetomii

Answer

Nocardia asteroides

Question 4

Which of the following fungi has not been cultured?

Accepted Answer

Rhinosporidium

Answer

Sporothrix

Answer

Acremonium

Answer

Blastomyces

Question 5

Tinea versicolor is typically associated with which organism?

Accepted Answer

Pityrosporum orbiculare

Answer

Candida infection

Answer

Epidermophyton

Answer

Trichophyton

Question 6

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 7

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

Question 8

A 63-year-old man with insulin-dependent diabetes develops a black, crusting lesion in the nose and left maxillary sinus. Biopsy reveals nonseptate hyphae. What is the diagnosis?

Accepted Answer

Mucor mycosis

Answer

Erysipelas

Answer

Eczema

Answer

Scarlet fever

Question 9

Which of the following represents a dimorphic fungus causing subcutaneous mycosis?

Accepted Answer

Sporotrichosis

Answer

Histoplasmosis

Answer

Rhinosporidiosis

Answer

Blastomycosis

Question 10

Pneumocystis carinii typically infects which host?

Accepted Answer

Rat

Answer

Human

Answer

Monkey

Answer

Cats

Mycology — MCQs

Mycology — MCQs

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