Mycology — MCQs
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An 18-year-old white male high-school student presents with a diffuse, painful rash on his thighs extending to his navel. He reports using topical hydrocortisone from a teammate for a previous groin rash. A KOH scraping of the current lesion shows hyaline hyphae. A schematic of the microscopic observation of the culture is provided. What is the most likely etiology?
What is the most important risk factor for invasive aspergillosis?
Renauld-Braud phenomenon is seen in which of the following?
Which of the following is NOT an 'all except' characteristic of acute pseudomembranous candidiasis?
Mycetoma is caused by the following agents except?
Which of the following stains is used to detect the capsule of Cryptococcus neoformans in a CSF sample?
Black coloured hard nodules in hair are produced by which organism?
A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings and the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?
Which staining method is used to identify Cryptococcus neoformans?
Which of the following is an occupational disease of gardeners?
Mycology Indian Medical PG Practice Questions and MCQs
Question 191: An 18-year-old white male high-school student presents with a diffuse, painful rash on his thighs extending to his navel. He reports using topical hydrocortisone from a teammate for a previous groin rash. A KOH scraping of the current lesion shows hyaline hyphae. A schematic of the microscopic observation of the culture is provided. What is the most likely etiology?
- A. Epidermophyton floccosum (Correct Answer)
- B. Microsporum canis
- C. Trichophyton rubrum
- D. Trichophyton tonsurans
Explanation: ***Epidermophyton floccosum*** - Produces characteristic **club-shaped macroconidia in clusters** with **NO microconidia**, which matches the microscopic culture morphology described. - Commonly causes **tinea cruris** (jock itch) that can spread to thighs and abdomen, especially when topical steroids are inappropriately used causing **tinea incognito**. *Microsporum canis* - Produces **spindle-shaped macroconidia** with **rough, thick walls** and **microconidia**, unlike the described morphology. - Typically causes **tinea capitis** and **tinea corporis** in children, often acquired from infected cats or dogs. *Trichophyton rubrum* - Shows **pencil-shaped macroconidia** and **abundant microconidia** on microscopy, different from the club-shaped pattern. - More commonly causes **chronic tinea pedis** and **onychomycosis** rather than acute groin infections. *Trichophyton tonsurans* - Produces **balloon-shaped microconidia** and few macroconidia, contrasting with the described morphology. - Primarily causes **tinea capitis** in children and is the most common cause of scalp ringworm in the United States.
Question 192: What is the most important risk factor for invasive aspergillosis?
- A. Profound neutropenia
- B. Tuberculosis
- C. Glucocorticoid use (Correct Answer)
- D. Antitumor necrosis factor therapy
Explanation: **Explanation:** The pathogenesis of **Invasive Aspergillosis (IA)** is primarily driven by the impairment of host immune defenses, specifically macrophages and neutrophils. While several factors contribute, **Glucocorticoid use** is considered the most significant risk factor in modern clinical practice due to its dual inhibitory effect. Steroids impair the ability of alveolar macrophages to kill inhaled conidia and inhibit the oxidative burst of neutrophils, which are essential for preventing hyphal germination and tissue invasion. * **Option A (Profound Neutropenia):** While neutropenia (Absolute Neutrophil Count <500/µL) is a classic and severe risk factor, especially in hematologic malignancies, epidemiological data and clinical guidelines (like IDSA) highlight that the widespread, prolonged use of high-dose corticosteroids across various conditions (transplants, autoimmune diseases, COPD) makes it the most frequent predisposing factor for IA. * **Option B (Tuberculosis):** TB is a risk factor for **Chronic Pulmonary Aspergillosis (CPA)** or the formation of an **Aspergilloma** (fungus ball) within pre-existing cavities, but it is not the primary driver for the *invasive* form of the disease. * **Option D (Anti-TNF therapy):** These agents increase the risk of granulomatous infections (like TB or Histoplasmosis) but are less commonly associated with IA compared to systemic steroids. **High-Yield NEET-PG Pearls:** 1. **Halo Sign:** The earliest radiological sign of IA on CT scan (a nodule surrounded by a ground-glass opacity representing hemorrhage). 2. **Galactomannan Assay:** A cell-wall antigen used as a serum/BAL biomarker for diagnosing IA. 3. **Drug of Choice:** **Voriconazole** is the gold standard for treating Invasive Aspergillosis. 4. **Morphology:** *Aspergillus* shows septate hyphae with **dichotomous branching at acute angles (45°)**.
Question 193: Renauld-Braud phenomenon is seen in which of the following?
- A. Candida albicans (Correct Answer)
- B. Candida pseudohyphae
- C. Histoplasma
- D. Cryptococcus
Explanation: **Explanation:** The **Renauld-Braud phenomenon** (also known as the **Germ Tube Test**) is a rapid diagnostic test used specifically to identify ***Candida albicans*** and *Candida dubliniensis*. **Why the correct answer is right:** When *Candida albicans* is incubated in human or animal serum at 37°C for 2–3 hours, it produces short, lateral outgrowths called **germ tubes**. These are the precursors to true hyphae. A key diagnostic feature of a true germ tube is that there is **no constriction** at the point of origin from the mother yeast cell. This specific morphological change is what defines the Renauld-Braud phenomenon. **Analysis of incorrect options:** * **Candida pseudohyphae:** While many *Candida* species produce pseudohyphae, these are characterized by **constrictions** at the septa (resembling a chain of sausages). The Renauld-Braud phenomenon specifically refers to the formation of *true* germ tubes without constrictions. * **Histoplasma:** This is a dimorphic fungus that exists as yeast in tissue and mold in culture. It does not produce germ tubes in serum; it is identified by small intracellular yeasts within macrophages. * **Cryptococcus:** This is an encapsulated yeast. It is identified by the **India Ink** preparation (showing a halo) or the Urease test. It does not form germ tubes. **High-Yield Clinical Pearls for NEET-PG:** * **Reynolds-Braud Phenomenon** = Germ Tube Test. * **Positive organisms:** *C. albicans* and *C. dubliniensis*. * **Culture Media:** *C. albicans* produces large, thick-walled **Chlamydospores** on **Cornmeal Agar**. * **Appearance on CHROMagar:** *C. albicans* appears **light green**. * **Rule of thumb:** If a *Candida* species is Germ Tube negative, it is classified as a "Non-albicans Candida" (NAC), such as *C. tropicalis* or *C. glabrata*.
Question 194: Which of the following is NOT an 'all except' characteristic of acute pseudomembranous candidiasis?
- A. Oral thrush
- B. Commonly occurs in immunocompromised patients
- C. May be associated with denture stomatitis (Correct Answer)
- D. Occurs in patients receiving systemic corticosteroid therapy
Explanation: **Explanation:** Acute Pseudomembranous Candidiasis, commonly known as **Oral Thrush**, is the most classic presentation of *Candida albicans* infection. The core concept to understand here is the classification of oral candidiasis into **Acute** and **Chronic** forms. **Why Option C is the correct answer:** Denture stomatitis is a form of **Chronic Atrophic Candidiasis** (also known as Chronic Erythematous Candidiasis). It is characterized by localized chronic erythema and edema of the mucosa covered by a denture. It is not a feature of the "Acute Pseudomembranous" type, which is defined by removable white plaques rather than chronic tissue changes under a prosthetic. **Analysis of Incorrect Options:** * **Option A (Oral Thrush):** This is the clinical synonym for acute pseudomembranous candidiasis. It presents as creamy white, "curd-like" patches on the tongue and buccal mucosa. * **Option B (Immunocompromised patients):** This is a hallmark characteristic. It is frequently seen in patients with HIV/AIDS (where it is an AIDS-defining illness), leukemia, or those undergoing chemotherapy. * **Option D (Systemic corticosteroids):** Prolonged use of systemic steroids or broad-spectrum antibiotics alters the oral flora and suppresses local immunity, acting as a major predisposing factor for the acute pseudomembranous form. **NEET-PG High-Yield Pearls:** * **The "Scrape Test":** The white pseudomembrane in thrush **can be scraped off** with a tongue depressor, leaving behind an erythematous or bleeding base. This distinguishes it from Oral Leukoplakia (which cannot be scraped off). * **Diagnosis:** Primarily clinical, but confirmed by KOH mount showing budding yeast cells and **pseudohyphae**. * **Treatment:** Topical Nystatin or Clotrimazole for mild cases; oral Fluconazole for moderate-to-severe or systemic cases.
Question 195: Mycetoma is caused by the following agents except?
- A. Allescheria boydii
- B. Madurella mycetomii
- C. Trichosporum beigelli (Correct Answer)
- D. Nocardia asteroides
Explanation: ### Explanation **Mycetoma** (Madura foot) is a chronic, granulomatous subcutaneous infection characterized by a triad of: **localized swelling, multiple interconnecting sinus tracts, and the discharge of grains.** It is caused by two distinct groups of organisms: 1. **Eumycetoma:** Caused by true fungi. 2. **Actinomycetoma:** Caused by aerobic actinomycetes (filamentous bacteria). #### Why Trichosporon beigelii is the Correct Answer: **Trichosporon beigelii** is the causative agent of **White Piedra**, a superficial mycosis characterized by soft, white-to-light-brown nodules on the hair shaft. It does not cause deep tissue invasion or the sinus tracts characteristic of mycetoma. #### Analysis of Incorrect Options: * **Allescheria boydii (Pseudallescheria boydii):** This is the most common fungal cause of eumycetoma worldwide. It typically produces **white/pale grains**. * **Madurella mycetomii:** This is the most common cause of fungal mycetoma (eumycetoma) globally, particularly in the "Mycetoma Belt." It is known for producing **black grains**. * **Nocardia asteroides:** This is a Gram-positive, filamentous, aerobic bacterium that causes **actinomycetoma**. It typically produces **yellowish-white grains**. #### High-Yield Clinical Pearls for NEET-PG: * **The "Dot-in-Circle" Sign:** A pathognomonic MRI finding for mycetoma where the "dot" represents the grain and the "circle" represents the surrounding inflammatory stroma. * **Grain Color Clues:** * **Black Grains:** Always Eumycetoma (*Madurella*, *Exophiala*). * **Red Grains:** *Actinomadura pelletieri*. * **Yellow/White Grains:** Can be either Actinomycetoma (*Nocardia*) or Eumycetoma (*Pseudallescheria*). * **Treatment:** Actinomycetoma (bacterial) responds well to antibiotics (e.g., Welsh regimen/Amikacin + Cotrimoxazole), whereas Eumycetoma (fungal) often requires long-term antifungals and surgical debridement.
Question 196: Which of the following stains is used to detect the capsule of Cryptococcus neoformans in a CSF sample?
- A. Gram stain
- B. Ziehl-Neelsen stain
- C. India ink preparation (Correct Answer)
- D. Methenamine-Silver stain
Explanation: **Explanation:** **Correct Answer: C. India ink preparation** *Cryptococcus neoformans* is a medically important yeast characterized by a thick, polysaccharide (glucuronoxylomannan) capsule. The **India ink preparation** is a classic **negative staining** technique used for rapid diagnosis. The carbon particles in the ink cannot penetrate the dense capsule; as a result, the yeast cells appear as clear, translucent halos against a dark, opaque background. This is a bedside test for Cryptococcal meningitis, particularly in immunocompromised patients (e.g., HIV/AIDS). **Analysis of Incorrect Options:** * **A. Gram stain:** While *Cryptococcus* is Gram-positive, the capsule does not stain well and may appear as an irregular "ghost" space. It is not the definitive method for capsule visualization. * **B. Ziehl-Neelsen (ZN) stain:** This is used to identify Acid-Fast Bacilli (AFB) like *Mycobacterium tuberculosis*. It does not highlight fungal capsules. * **D. Methenamine-Silver (GMS) stain:** This is an excellent stain for visualizing the fungal **cell wall** (turning it black), but it does not specifically demonstrate the capsule. **High-Yield NEET-PG Pearls:** * **Most Sensitive Test:** While India ink is specific, the **Cryptococcal Antigen (CrAg)** test (Lateral Flow Assay or Latex Agglutination) is the most sensitive method for diagnosis. * **Culture:** Sabouraud Dextrose Agar (SDA) shows creamy, mucoid colonies. Niger seed (Birdseed) agar is used to demonstrate **urease activity** and melanin production (brown-black colonies). * **Histopathology:** In tissue sections, the capsule can be specifically stained using **Mucicarmine** (appears bright red) or **Alcian blue**. * **Clinical Sign:** "Soap bubble" lesions in the basal ganglia on MRI are characteristic of CNS cryptococcosis.
Question 197: Black coloured hard nodules in hair are produced by which organism?
- A. Piedraia hortae (Correct Answer)
- B. Epidermophyton floccosum
- C. Hortaea werneckii
- D. Malassezia furfur
Explanation: **Explanation:** The question describes the classic clinical presentation of **Black Piedra**, a superficial fungal infection of the hair shaft. **1. Why Piedraia hortae is correct:** *Piedraia hortae* is a dematiaceous (pigmented) fungus that causes **Black Piedra**. It produces **hard, black, gritty nodules** that are firmly attached to the hair shaft, primarily on the scalp. Under microscopy, these nodules consist of a dense mass of hyphae and contain asci with ascospores. **2. Why the other options are incorrect:** * **Epidermophyton floccosum:** This is a dermatophyte that causes Tinea infections (like Tinea cruris or pedis). It involves the skin and nails but does not form hard nodules on the hair shaft. * **Hortaea werneckii:** This fungus causes **Tinea nigra**, which presents as painless, brown-to-black macules on the **palms and soles**, not as hair nodules. * **Malassezia furfur:** This yeast causes **Pityriasis versicolor** (hypo/hyperpigmented scaly patches) and Seborrheic dermatitis. It does not produce hard nodules on hair. **3. High-Yield Clinical Pearls for NEET-PG:** * **Black Piedra vs. White Piedra:** While *Piedraia hortae* causes Black Piedra (hard, black nodules), **Trichosporon beigelii** causes **White Piedra** (soft, white-to-light brown nodules, usually on axillary or pubic hair). * **Tinea Nigra Diagnosis:** Look for "2-streamed" or branched septate hyphae and arthroconidia on KOH mount. * **Pityriasis Versicolor Diagnosis:** Characterized by the "Spaghetti and Meatball" appearance (short curved hyphae and yeast cells) on KOH mount. * **Wood’s Lamp:** *Malassezia furfur* shows a characteristic golden-yellow fluorescence.
Question 198: A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings and the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?
- A. Candida albicans (Correct Answer)
- B. Cytomegalovirus
- C. Herpes simplex I
- D. Human herpesvirus 8
Explanation: **Explanation:** The clinical presentation of white, plaque-like material on the tongue and buccal mucosa that can be scraped off is classic for **Oral Candidiasis (Thrush)**. In an HIV-positive patient, the progression from oral involvement to painful swallowing (odynophagia) indicates **Esophageal Candidiasis**, which is an **AIDS-defining illness**. **Why Candida albicans is correct:** * **Clinical Presentation:** It presents as creamy white curd-like patches (pseudomembranes) that, when scraped, may leave an erythematous or bleeding base. * **Microscopy:** Laboratory findings typically show budding yeast cells and **pseudohyphae**. It is the most common opportunistic fungal infection in HIV patients. * **Significance:** While oral thrush can occur at CD4 counts <500 cells/mm³, esophageal involvement usually signifies a CD4 count **<200 cells/mm³**, marking the transition to AIDS. **Why other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV can cause esophagitis in AIDS patients (CD4 <50), it typically presents with **large, shallow linear ulcers**, not white plaques. * **Herpes simplex I (HSV-1):** HSV esophagitis presents with small, deep **"punched-out" ulcers** and characteristic Cowdry type A inclusion bodies, not scrapable plaques. * **Human herpesvirus 8 (HHV-8):** This is the causative agent of **Kaposi Sarcoma**, which presents as reddish-purple macules or nodules, not white plaques. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** Positive for *C. albicans* (formation of true hyphae from yeast cells in serum at 37°C). * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white colonies. * **Treatment:** Oral Fluconazole is the first-line treatment for esophageal candidiasis; Nystatin "swish and swallow" is used for mild oral thrush.
Question 199: Which staining method is used to identify Cryptococcus neoformans?
- A. Acid-fast bacilli (AFB) stain
- B. Gram stain
- C. India ink stain (Correct Answer)
- D. Rose Bengal stain
Explanation: **Explanation:** **Correct Answer: C. India ink stain** *Cryptococcus neoformans* is an encapsulated yeast. The **India ink stain** (negative staining) is the classic method used to visualize this capsule. The large polysaccharide capsule does not take up the ink particles, resulting in a characteristic **"halo" appearance** against a dark, opaque background. In a clinical setting, this is typically performed on Cerebrospinal Fluid (CSF) to diagnose Cryptococcal meningitis, especially in immunocompromised patients (e.g., HIV/AIDS). **Incorrect Options:** * **A. Acid-fast bacilli (AFB) stain:** Used primarily for *Mycobacterium tuberculosis* and *Nocardia*. While some fungi like *Histoplasma* can be weakly acid-fast, it is not used for *Cryptococcus*. * **B. Gram stain:** *Cryptococcus* appears Gram-positive (purple), but the stain often shows irregular "star-gazing" patterns and does not reliably demonstrate the diagnostic capsule. * **D. Rose Bengal stain:** This is a diagnostic dye used primarily in ophthalmology to detect corneal epithelial damage or in the Rose Bengal Plate Test (RBPT) for *Brucellosis* screening. **High-Yield NEET-PG Pearls:** * **Most Sensitive Test:** While India ink is classic, the **Cryptococcal Antigen (CrAg)** test (Latex agglutination or Lateral Flow Assay) is more sensitive and is now the preferred screening method. * **Culture:** Sabouraud Dextrose Agar (SDA) is used; colonies are typically mucoid (due to the capsule). * **Other Stains:** **Mucicarmine stain** is specific for the capsule (stains it red) in tissue sections. **Masson-Fontana stain** can detect melanin in the cell wall. * **Urease Test:** *Cryptococcus* is **Urease positive**, which helps differentiate it from *Candida*.
Question 200: Which of the following is an occupational disease of gardeners?
- A. Candidiasis
- B. Sporotrichosis (Correct Answer)
- C. Histoplasmosis
- D. Cryptococcosis
Explanation: **Explanation** **Sporotrichosis** is the correct answer because it is caused by the dimorphic fungus *Sporothrix schenckii*, which is found in soil, decaying vegetation, and thorny plants (like rose bushes). It is classically known as **"Rose Gardener’s Disease"** because infection typically occurs via traumatic inoculation (e.g., a thorn prick) while gardening or farming. * **Pathogenesis:** Following inoculation, it causes a localized primary nodule that often ulcerates. It then spreads via the lymphatic system, leading to a chain of nodules along the drainage path (**Lymphocutaneous sporotrichosis**). **Why other options are incorrect:** * **Candidiasis:** Caused by *Candida albicans*, an opportunistic endogenous fungus. It is part of the normal flora and is not specifically linked to gardening. * **Histoplasmosis:** Caused by *Histoplasma capsulatum*, found in soil enriched with **bird or bat droppings** (guano). It is associated with cave explorers (spelunkers) or cleaning chicken coops, rather than gardening. * **Cryptococcosis:** Caused by *Cryptococcus neoformans*, primarily associated with **pigeon droppings**. It is an opportunistic infection commonly seen in immunocompromised patients (e.g., HIV/AIDS). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** At 25°C (mold form), it shows delicate hyphae with **"flower-like" or "daisy-petal"** arrangements of conidia. At 37°C (yeast form), it appears as **cigar-shaped bodies**. * **Asteroid Bodies:** In tissue sections, a central yeast cell surrounded by eosinophilic radiating processes (Splendore-Hoeppli phenomenon) may be seen. * **Treatment:** The drug of choice for cutaneous sporotrichosis is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.
Practice by Chapter
Classification of Fungi
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Superficial Mycoses
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Dermatophytes
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Subcutaneous 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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Antifungal Agents
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Laboratory Diagnosis of Fungal Infections
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