Zygomycosis — MCQs
A forest officer develops the lesion as shown in the image. Which of the following is not a differential to consider?
Mucormycosis of the paranasal sinus is most common in?
Which organism can penetrate corneal endothelium?
What is the treatment of choice for oral candidiasis?
A 65-year-old diabetic man presents with black necrotic tissue on his palate. What is the most likely causative organism?
In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?
A 60-year-old female with a history of diabetes presents with nasal congestion, facial pain, and black necrotic patches on the palate. What is the most likely diagnosis?
Beta 1,3 Glucan test is positive in all except?
Which statement is false regarding Cryptococcus neoformans?
Which of the following is a non-culturable fungus?
Zygomycosis Indian Medical PG Practice Questions and MCQs
Question 1: A forest officer develops the lesion as shown in the image. Which of the following is not a differential to consider?
- A. Cutaneous anthrax
- B. KFD (Correct Answer)
- C. Scrub typhus
- D. Healing brown recluse spider bite
Explanation: ***KFD*** - **Kyasanur Forest Disease** (KFD) is a viral hemorrhagic fever, but it does **not** typically present with a **skin lesion** or eschar like the one shown. - KFD is characterized by fever, headache, myalgia, and gastrointestinal symptoms, with hemorrhagic manifestations in severe cases, but not a primary cutaneous lesion. *Cutaneous anthrax* - **Cutaneous anthrax** commonly presents as an **eschar**, often with surrounding edema and vesicles, which can resemble the lesion in the image. - Exposure through handling infected animal products or contact with contaminated soil is common, aligning with a forest officer's occupation. *Scrub typhus* - **Scrub typhus** characteristically causes an **eschar** (tache noire) at the bite site of the chigger mite. - The lesion in the image, an ulcer with a central black crust, is highly suggestive of such an eschar seen in rickettsial infections. *Healing brown recluse spider bite* - A **brown recluse spider bite** can cause a **necrotic ulcer** with a central dark eschar as the wound heals, fitting the appearance of the lesion. - The profession of a forest officer increases the likelihood of exposure to spiders in their natural habitat.
Question 2: Mucormycosis of the paranasal sinus is most common in?
- A. Diabetes (Correct Answer)
- B. Individuals with HIV
- C. Individuals on immunosuppressive therapy
- D. Patients who have undergone surgery
Explanation: Diabetes - **Diabetic ketoacidosis** significantly impairs neutrophil function, reducing the body's ability to resist fungal infections like mucormycosis. [1] - The **hyperglycemic** and **acidotic** environment in uncontrolled diabetes promotes the growth and invasiveness of Mucorales fungi. [1] *Individuals with HIV* - While HIV can lead to **immunocompromise**, mucormycosis is less common in this population than in those with diabetes; other opportunistic infections are more prevalent with HIV. - HIV primarily affects **CD4+ T-lymphocytes**, whereas mucormycosis is more often associated with defects in phagocytic function. *Individuals on immunosuppressive therapy* - **Immunosuppressive therapy**, such as corticosteroids or chemotherapy, can increase the risk of fungal infections, but **uncontrolled diabetes** is the most significant risk factor for rhinocerebral mucormycosis. [1] - The type of immunosuppression and underlying condition are critical; while relevant, it is not as uniquely predisposing as diabetic ketoacidosis. [1] *Patients who have undergone surgery* - Surgical patients, especially those with prolonged hospital stays or extensive wounds, can be susceptible to various infections, but mucormycosis is not specifically or most commonly linked to surgery as an isolated risk factor. - **Nosocomial infections** after surgery are often bacterial; fungal infections, when they occur, are typically associated with profound immunosuppression or specific device-related issues, not surgery alone.
Question 3: Which organism can penetrate corneal endothelium?
- A. Staphylococcus Aureus
- B. Haemophilus influenzae (Correct Answer)
- C. Aspergillus fumigatus
- D. Neisseria gonorrhoeae
Explanation: ***Haemophilus influenzae*** - *Haemophilus influenzae* is unique in its ability to penetrate the **intact corneal endothelium** through its specific virulence factors and enzymatic mechanisms. - Along with *Neisseria meningitidis*, it can breach the **Descemet's membrane and endothelial barrier** without requiring prior epithelial damage. - This property makes it particularly dangerous as it can cause **endophthalmitis** by directly accessing the anterior chamber. *Neisseria gonorrhoeae* - While highly virulent, *N. gonorrhoeae* penetrates the **corneal epithelium** (outer layer) through its proteases, not the endothelium (inner layer). - It causes severe **hyperacute conjunctivitis** and can lead to **corneal perforation**, but via epithelial destruction and stromal infiltration. *Staphylococcus aureus* - A common cause of **bacterial keratitis** following epithelial defects or trauma. - Causes stromal infiltration and abscess formation but **cannot penetrate intact endothelium**. *Aspergillus fumigatus* - This fungus causes **fungal keratitis** typically after trauma with vegetative matter. - Invades through **epithelial breaches** and stromal infiltration, not through intact endothelial penetration.
Question 4: What is the treatment of choice for oral candidiasis?
- A. Griesofulvin
- B. Terbinafin
- C. Fluconazole (Correct Answer)
- D. Selenium sulphide
Explanation: **Fluconazole** - **Fluconazole** is an **antifungal drug** that is frequently used as the treatment of choice for **oral candidiasis**, particularly in cases that are moderate to severe or resistant to topical treatments. - It is available orally and effectively targets **Candida species** by inhibiting ergosterol synthesis, a key component of the fungal cell membrane. *Terbinafine* - **Terbinafine** is primarily an **antifungal drug** used to treat **dermatophyte infections**, such as those affecting the skin and nails (e.g., ringworm, athlete's foot, onychomycosis). - It is less effective against **Candida species**, which are the cause of oral candidiasis. *Griseofulvin* - **Griseofulvin** is an **oral antifungal** specifically effective against **dermatophytes** (tinea infections) by interfering with fungal cell division. - It is not effective against **Candida infections**, making it an inappropriate choice for oral candidiasis. *Selenium sulfide* - **Selenium sulfide** is an **antifungal agent** predominantly used as a topical treatment for **seborrheic dermatitis** and **tinea versicolor** due to its antifungal and cytostatic properties. - It is not indicated for the treatment of **oral candidiasis**, which requires systemic or topical oral antifungal medications.
Question 5: A 65-year-old diabetic man presents with black necrotic tissue on his palate. What is the most likely causative organism?
- A. Cryptococcus neoformans
- B. Candida albicans
- C. Mucor species (Correct Answer)
- D. Aspergillus fumigatus
Explanation: ***Mucor species*** - The presence of **black necrotic tissue** on the palate in a diabetic patient is highly suggestive of **mucormycosis**, an aggressive fungal infection caused by *Mucor* species. - **Diabetes mellitus**, particularly with ketoacidosis, is a major risk factor for mucormycosis due to impaired phagocytic function and increased iron availability. *Cryptococcus neoformans* - This fungus is primarily associated with **cryptococcal meningitis** or pneumonia, especially in immunocompromised individuals. - It does not typically cause **black necrotic lesions** on the palate. *Candida albicans* - While *Candida albicans* can cause oral infections (**thrush**), these typically present as white, creamy patches that can be scraped off, not black necrotic tissue. - Oral candidiasis is common in diabetics but does not usually involve tissue necrosis. *Aspergillus fumigatus* - *Aspergillus* species can cause invasive infections, particularly in immunocompromised patients, often affecting the lungs or sinuses. - While it can cause **necrotic lesions**, the characteristic rapid progression and specific presentation in the palate of a diabetic with black necrotic tissue points more strongly towards *Mucor*.
Question 6: In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?
- A. Aspergillus (Correct Answer)
- B. Mucor
- C. Penicillium
- D. Candida
Explanation: ***Aspergillus*** - *Aspergillus* species are characterized by their distinctive **acute-angled (dichotomous) septate hyphae** when observed microscopically in tissue sections or clinical samples. - This morphological feature is crucial for differentiating *Aspergillus* infections, such as **aspergillosis**, from other fungal infections. *Mucor* - *Mucor* (along with *Rhizopus* and *Lichtheimia*) belongs to the Zygomycetes class, which are characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching, not acute-angled septate hyphae. - These fungi are associated with **mucormycosis**, often seen in immunocompromised patients, particularly those with diabetes. *Penicillium* - *Penicillium* is a common mold known for producing penicillin and typically appears as **septate hyphae** but is more often recognized by its branching, brush-like conidiophores (penicilli) in culture rather than a distinct acute-angled septate hyphal morphology in clinical samples causing invasive disease. - While it can cause opportunistic infections, its hyphae are less commonly described as having uniquely acute angles compared to *Aspergillus*. *Candida* - *Candida* species are typically observed as **yeast cells (oval budding forms)**, often forming **pseudohyphae** (elongated yeast cells that remain attached) or true hyphae under specific conditions, but not as acute-angled septate hyphae. - *Candida* is a common cause of superficial and invasive candidiasis, and its microscopic appearance is distinct from filamentous fungi.
Question 7: A 60-year-old female with a history of diabetes presents with nasal congestion, facial pain, and black necrotic patches on the palate. What is the most likely diagnosis?
- A. Bacterial sinusitis
- B. Mucormycosis (Correct Answer)
- C. Rhinoscleroma
- D. Granulomatosis with Polyangiitis (GPA)
Explanation: ***Mucormycosis*** - The presence of **black necrotic patches on the palate** in a diabetic patient with sinusitis symptoms is highly characteristic of mucormycosis. - **Diabetes** is a significant risk factor for this aggressive fungal infection, which often presents with tissue necrosis. *Bacterial sinusitis* - While facial pain and nasal congestion are consistent with bacterial sinusitis, **black necrotic patches** are not a typical feature. - Bacterial sinusitis rarely causes deep tissue invasion and necrosis of this extent. *Rhinoscleroma* - This is a chronic granulomatous disease of the upper respiratory tract caused by *Klebsiella rhinoscleromatis*, primarily seen in specific endemic regions. - It presents with **progressive inflammatory masses** and **scarring**, not acute necrosis or black patches. *Granulomatosis with Polyangiitis (GPA)* - GPA can cause sinusitis, **nasal crusting**, and **cartilage destruction**, but typically presents with **granulomatous inflammation** and vasculitis, not primary necrotic patches on the palate. - It is often associated with **ANCA positivity** and systemic symptoms affecting the lungs and kidneys.
Question 8: Beta 1,3 Glucan test is positive in all except?
- A. Pneumocystis Jirovecii
- B. Candida
- C. Mucormycosis (Correct Answer)
- D. Aspergillus
Explanation: ***Mucormycosis*** - Fungi causing mucormycosis belong to the order **Mucorales**, which structurally lack **beta-D-glucan** in their cell walls. - Due to the absence of beta-D-glucan, the **beta-1,3-D-glucan assay** will yield a negative result in cases of mucormycosis. *Pneumocystis jirovecii* - This fungus contains significant amounts of **beta-D-glucan** in its cell wall, making the test usually positive during active infection. - A positive **beta-D-glucan test** can be a useful diagnostic marker for **Pneumocystis pneumonia (PCP)**, especially in immunocompromised patients. *Candida* - **Candida species** possess a cell wall rich in **beta-D-glucan**, leading to a positive test result during active infection. - The **beta-D-glucan assay** is a valuable adjunctive test for diagnosing invasive candidiasis. *Aspergillus* - The cell wall of **Aspergillus** contains **beta-D-glucan**, causing the test to be positive in cases of invasive aspergillosis. - A positive **beta-D-glucan test** can aid in the early diagnosis and management of invasive aspergillosis, particularly in high-risk patients.
Question 9: Which statement is false regarding Cryptococcus neoformans?
- A. Grows at 5°C and 37°C
- B. Has 4 serotypes
- C. Urease negative (Correct Answer)
- D. Causes superficial skin infection
Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast primarily associated with pigeon droppings and is a significant opportunistic pathogen in immunocompromised patients (e.g., HIV/AIDS). **1. Why "Urease negative" is the False Statement:** *Cryptococcus neoformans* is characteristically **Urease positive**. The production of the urease enzyme is a key biochemical marker used in the laboratory to differentiate it from other yeasts like *Candida albicans* (which is urease negative). It hydrolyzes urea to produce ammonia, raising the pH and changing the indicator color. **2. Analysis of Other Options:** * **Option A (Grows at 5°C and 37°C):** This is true. Unlike many other pathogenic fungi, *C. neoformans* can grow at 37°C (essential for human pathogenicity) and also at lower temperatures like 4°C–5°C. * **Option B (Has 4 serotypes):** This is true. Based on capsular polysaccharide antigens, it is classified into four serotypes: **A, B, C, and D**. (Note: Serotype A is *C. neoformans var. grubii*, while B and C are now often classified as *C. gattii*). * **Option D (Causes superficial skin infection):** This is true. While meningitis is the most common presentation, primary or secondary cutaneous cryptococcosis can occur, presenting as papules, pustules, or ulcerations. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **Polysaccharide capsule** (Glucuronoxylomannan) is the most important; it inhibits phagocytosis. * **Staining:** **India Ink** preparation shows a "halo" (negative staining). **Mucicarmine** stains the capsule red. * **Culture:** Grows on **Bird Seed Agar** (Niger Seed Agar) producing brown/black colonies due to **Phenoloxidase** activity (melanin production). * **Drug of Choice:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.
Question 10: Which of the following is a non-culturable fungus?
- A. Rhinosporidium (Correct Answer)
- B. Candida
- C. Sporothrix
- D. Penicillium
Explanation: **Explanation:** The correct answer is **Rhinosporidium seeberi**. This organism is unique in medical mycology because it has **never been successfully cultured** on artificial laboratory media (like SDA) or in cell culture. Its classification was historically debated, but molecular analysis (18S rRNA sequencing) has placed it among the *Mesomycetozoea*, a group of aquatic fish parasites, though it is still traditionally studied in Mycology. **Why the other options are incorrect:** * **Candida:** A common yeast that grows readily on Sabouraud Dextrose Agar (SDA) within 24–48 hours, forming creamy white colonies. * **Sporothrix:** A dimorphic fungus that can be cultured at 25°C (mold form with "flower-like" sporulation) and 37°C (yeast form). * **Penicillium:** A common saprophytic mold that grows rapidly in culture, characterized by its "brush-like" conidiophores. **High-Yield Clinical Pearls for NEET-PG:** * **Disease:** Rhinosporidiosis typically presents as **friable, leafy, strawberry-like polypoid masses** in the nose or nasopharynx. * **Transmission:** Associated with bathing in stagnant freshwater (ponds/tanks). * **Diagnosis:** Since it cannot be cultured, diagnosis relies on **histopathology**. Look for large **sporangia** (up to 350 µm) containing thousands of **endospores**. * **Treatment:** Surgical excision with wide-base cauterization is the treatment of choice; medical therapy (Dapsone) has limited efficacy.
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