Mycology Practice Questions

Q: All of the following statements about thrush are true EXCEPT?

It is caused by a gram-negative fungus. **Explanation:** **1. Why Option A is the correct (False) statement:** Thrush is caused by *Candida albicans*, which is a **Gram-positive** yeast. In microbiology, all fungi, including *Candida*, stain Gram-positive because their thick cell walls (containing chitin and glucans) retain the crystal violet dye. Therefore, the statement that it is caused by a "gram-negative fungus" is scientifically incorrect. **2. Analysis of other options:** * **Option B:** Oral thrush (pseudomembranous candidiasis) is characterized by creamy white "curd-like" plaques. These plaques consist of a dense network of fungal hyphae, pseudohyphae, proliferating desquamated epithelial cells, bacteria, and fibrin. * **Option C:** *Candida* is an opportunistic pathogen. Thrush is frequently seen in patients with compromised immunity (HIV/AIDS), those using inhaled corticosteroids, or those with systemic diseases like Diabetes Mellitus. * **Option D:** Neonatal thrush can occur during birth (via the maternal vaginal canal) or spread in nurseries. In institutional settings, it can indeed occur in an epidemic fashion due to cross-contamination via the hands of healthcare workers or contaminated feeding equipment. **High-Yield Clinical Pearls for NEET-PG:** * **The "Scrape" Test:** Unlike leukoplakia, the white plaques of oral thrush **can be scraped off**, leaving behind an erythematous, bleeding base. * **Morphology:** On KOH mount, *Candida* shows budding yeast cells and **pseudohyphae**. * **Drug of Choice:** For mild oral thrush, topical **Clotrimazole** or **Nystatin** suspension is used. For systemic or refractory cases, **Fluconazole** is the preferred agent. * **Risk Factor:** Chronic use of broad-spectrum antibiotics predisposes patients to thrush by altering the normal oral flora.

Q: Which of the following is NOT a characteristic of Cryptococcus neoformans?

A non-encapsulated fungus that infects humans. **Explanation:** The correct answer is **A**. *Cryptococcus neoformans* is defined by its **prominent polysaccharide capsule**, which is its most important virulence factor. This capsule is composed primarily of glucuronoxylomannan (GXM), which inhibits phagocytosis and allows the yeast to evade the host immune system. In clinical practice, this capsule is visualized using **India Ink preparation**, appearing as a clear halo against a dark background. **Analysis of other options:** * **Option B:** It is the most common cause of fungal meningitis, particularly in immunocompromised individuals (HIV/AIDS patients with CD4 counts <100 cells/μL). * **Option C:** *C. neoformans* produces the enzyme **phenoloxidase (laccase)**, which converts phenolic compounds into **melanin**. Melanin protects the fungus from oxidative stress and host immune responses, making it a key virulence factor. This property is used for identification on **Niger Seed (Birdseed) Agar**, where colonies appear brown/black. * **Option D:** Taxonomically, *Cryptococcus* is a **Basidiomycete** yeast. Its sexual state (teleomorph) is known as *Filobasidiella neoformans*. **High-Yield NEET-PG Pearls:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **Latex Agglutination Test** (detects capsular antigen) is more sensitive than India Ink. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as mucoid, cream-colored colonies. It is **Urease positive**. * **Treatment:** Induction therapy with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: White piedra is caused by which of the following fungi?

Trichosporon beigelii. **Explanation:** **White Piedra** is a superficial fungal infection of the hair shaft characterized by soft, white to light brown nodules. The correct answer is **Trichosporon beigelii** (now often reclassified as *Trichosporon asahii* or other *Trichosporon* species). These nodules are loosely attached to the hair shaft and are composed of hyphae and blastoconidia. It primarily affects the hair of the beard, mustache, and pubic area. **Analysis of Options:** * **A. Piedraia hortae:** This is the causative agent of **Black Piedra**. Unlike white piedra, it produces hard, black, firmly adherent nodules, typically on the scalp hair. * **B. Malassezia globosa:** This lipophilic yeast is the most common cause of **Pityriasis versicolor** (Tinea versicolor), characterized by hypo- or hyperpigmented scaly macules on the trunk. * **C. Hortaea werneckii:** This is the causative agent of **Tinea nigra**, a superficial infection presenting as dark, brownish-black macules on the palms and soles. **NEET-PG High-Yield Pearls:** * **Diagnosis:** Microscopic examination (KOH mount) of white piedra shows transparent hyphae and **arthroconidia**. * **Treatment:** The treatment of choice for both types of Piedra is shaving or cutting the hair. Topical antifungals (azoles) can also be used. * **Differential:** Do not confuse Piedra with **Pediculosis capitis** (nits are oval and on one side of the shaft) or **Trichomycosis axillaris** (caused by *Corynebacterium*, not a fungus). * **Key Distinction:** White Piedra = Soft/Loose/Trichosporon; Black Piedra = Hard/Adherent/Piedraia.

Q: All of the following are true about Candida EXCEPT:

It is a mould. **Explanation:** The correct answer is **C (It is a mould)**. *Candida* species are primarily classified as **yeasts**, not moulds. **1. Why Option C is the correct "Except":** *Candida* is a unicellular fungus (yeast) that reproduces by budding. Unlike moulds, which are multicellular filamentous fungi consisting of true hyphae (e.g., *Aspergillus* or *Rhizopus*), *Candida* exists predominantly in yeast form. While it can form "pseudohyphae," it does not fit the structural definition of a mould. **2. Analysis of Other Options:** * **Option A (Pseudohyphae are seen):** This is **true**. Pseudohyphae are formed when buds fail to detach and elongate, creating a "sausage-link" appearance with distinct constrictions at the septa. (Note: *C. glabrata* is the only medically important species that does *not* form pseudohyphae). * **Option B (Produces chlamydospores):** This is **true**. Under specific conditions (e.g., growth on Cornmeal agar at 25°C), *Candida albicans* and *C. dubliniensis* produce thick-walled, resting spores called chlamydospores. * **Option D (Non-thermally dimorphic):** This is **true**. Unlike "true" dimorphic fungi (like *Histoplasma*) which change form based on temperature (yeast at 37°C, mould at 25°C), *Candida* is **pleomorphic**. It can form yeast, pseudohyphae, and true hyphae (germ tubes) within the same temperature range, often triggered by pH or nutrient changes. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test (Reynolds-Braude Phenomenon):** The definitive rapid diagnostic test for *C. albicans*. * **C. glabrata:** Increasing in incidence; notably lacks pseudohyphae and is often resistant to azoles. * **C. auris:** A multi-drug resistant emerging pathogen causing hospital outbreaks. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white, smooth colonies with a "yeasty" odor.

Q: Which fungus is typically not isolated in standard culture media?

Pneumocystis jiroveci. **Explanation:** The correct answer is **D. Pneumocystis jiroveci**. **Why it is correct:** *Pneumocystis jiroveci* is an atypical fungus that lacks ergosterol in its cell membrane and cannot be grown on standard fungal culture media (like Sabouraud Dextrose Agar). It is an **obligate extracellular parasite** that requires specific cell culture systems or animal models for growth, which are not used in routine clinical diagnostics. Diagnosis relies primarily on microscopic visualization (using GMS or Periodic acid-Schiff stains) of cysts or trophozoites in bronchoalveolar lavage (BAL) fluid or induced sputum, or via PCR. **Why the other options are incorrect:** * **A. Cryptococcus:** *Cryptococcus neoformans* grows readily on SDA and specialized media like Bird Seed Agar (Niger seed agar), where it produces characteristic brown-pigmented colonies due to phenoloxidase activity. * **B. Dermatophytes:** Fungi such as *Trichophyton*, *Microsporum*, and *Epidermophyton* are routinely isolated on SDA or Dermatophyte Test Medium (DTM), which contains phenol red as a pH indicator. * **C. Candida:** *Candida albicans* and other species are the most common fungi isolated in clinical labs. They grow rapidly (24–48 hours) on SDA and Blood Agar, forming creamy white colonies. **High-Yield Clinical Pearls for NEET-PG:** * **Stains for Pneumocystis:** Gomori Methenamine Silver (GMS) is the gold standard (stains cysts black/brown). * **Treatment of Choice:** Trimethoprim-Sulfamethoxazole (TMP-SMX), not standard antifungals, because it lacks ergosterol. * **CD4 Count:** Infection is typically seen in HIV patients when the CD4 count falls below **200 cells/mm³**. * **Radiology:** Characterized by bilateral "ground-glass opacities" on chest X-ray.

Q: Which statement is NOT true about Cryptococcus neoformans?

Is urease negative. **Explanation:** *Cryptococcus neoformans* is an encapsulated opportunistic yeast that is a frequent cause of meningitis, especially in immunocompromised patients (e.g., HIV/AIDS). **Why Option D is the correct answer:** *Cryptococcus neoformans* is **Urease positive**. This is a key biochemical characteristic used for its identification in the laboratory. The enzyme urease hydrolyzes urea into ammonia and carbon dioxide, increasing the pH and turning Christensen’s urea agar pink. Therefore, the statement "Is urease negative" is incorrect. **Analysis of other options:** * **Option A (Grows at 37°C):** Unlike many saprophytic fungi, *C. neoformans* is thermotolerant and grows well at 37°C. This ability to grow at human body temperature is a vital virulence factor. * **Option B (Grows on Sabouraud's agar):** It grows readily on Sabouraud Dextrose Agar (SDA), typically forming cream-colored, mucoid colonies (due to the capsule) within 48–72 hours. * **Option C (Has a polysaccharide capsule):** This is the most defining feature of *Cryptococcus*. The thick glucuronoxylomannan capsule is antiphagocytic and is visualized using **India Ink** (negative staining), where it appears as a clear halo against a dark background. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **Latex Agglutination test** for capsular antigen is more sensitive than India Ink. * **Culture:** On **Niger Seed Agar** (Birdseed agar), it produces brown/black colonies due to phenoloxidase activity (melanin production). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: A HIV positive patient presents with cough for 10 days. Sputum culture by SDA reveals broad budding yeast. What is the diagnosis?

Blastomycosis. **Explanation:** The diagnosis is **Blastomycosis**, caused by the dimorphic fungus *Blastomyces dermatitidis*. The key diagnostic feature mentioned in the question is the presence of **broad-based budding yeast** (the daughter cell is attached to the parent cell by a wide neck). **Why Blastomycosis is correct:** In tissue or culture at 37°C (SDA), *Blastomyces* appears as large, thick-walled, spherical yeast cells. The characteristic "broad base" attachment between the bud and the parent cell is pathognomonic. It typically presents as a pulmonary infection (cough, fever) and is an opportunistic infection in immunocompromised individuals, such as HIV-positive patients. **Why other options are incorrect:** * **Histoplasma capsulatum:** Characterized by **small, intracellular yeast** cells (found within macrophages) with narrow-based budding. It does not show broad-based buds. * **Coccidioidomycosis:** Characterized by **spherules containing endospores** in tissue samples, not budding yeast. * **Paracoccidioidomycosis:** Characterized by large yeast cells with multiple buds, often described as a **"Pilot’s wheel"** or "Mickey Mouse" appearance, rather than a single broad-based bud. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Blastomyces:** **B**lasto = **B**ig, **B**lue, **B**road-**B**ased **B**uds. * **Geographic distribution:** Often associated with the Ohio and Mississippi River valleys (similar to Histoplasma). * **Systemic involvement:** In disseminated cases, it frequently involves the **skin** (verrucous lesions) and **bones**. * **Staining:** Best visualized using Silver stains (GMS) or PAS stain.

Q: A patient suffering from AIDS presents with a history of dyspnea and non-productive cough. X-ray shows bilateral perihilar opacities without pleural effusion and lymphadenopathy. What is the most probable etiological agent?

Pneumocystis jirovecii. ### Explanation The clinical presentation of a patient with AIDS, progressive dyspnea, and a non-productive cough, combined with the classic radiological finding of **bilateral perihilar (interstitial) opacities**, is the hallmark of **Pneumocystis jirovecii Pneumonia (PCP)**. **1. Why Pneumocystis jirovecii is correct:** PCP is the most common opportunistic infection in HIV patients with CD4 counts <200 cells/µL. The characteristic X-ray shows "ground-glass" or "bat-wing" perihilar infiltrates [1]. The absence of pleural effusion and lymphadenopathy is a key negative finding that strongly points toward PCP rather than bacterial or mycobacterial infections [1]. **2. Why other options are incorrect:** * **Tuberculosis (TB):** While common in AIDS, TB typically presents with upper lobe cavitary lesions (in early HIV) or mediastinal lymphadenopathy and pleural effusions (in advanced HIV) [1]. * **CMV Pneumonitis:** Though it causes interstitial patterns, it is rare as a primary cause of pneumonia in HIV unless the CD4 count is extremely low (<50 cells/µL) and is usually a diagnosis of exclusion. * **Kaposi’s Sarcoma:** Pulmonary involvement usually presents with nodular opacities, pleural effusions (often hemorrhagic), and characteristic skin lesions [2]. **3. NEET-PG High-Yield Pearls:** * **Diagnosis:** The gold standard is identifying the organism via **Gomori Methenamine Silver (GMS) stain** from induced sputum or Bronchoalveolar Lavage (BAL) [1]. * **Biomarker:** Elevated **Serum LDH** is a sensitive but non-specific marker for PCP. * **Treatment:** Drug of choice is **High-dose TMP-SMX** [1]. * **Steroid Indication:** Add Prednisone if $PaO_2 35$ mmHg to prevent respiratory failure triggered by inflammatory response to dying organisms [1].

Q: Tinea pedis is caused by which of the following?

E. floccosum. **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*.

Q: Which type of hyphae is characteristic of Aspergilloma?

Septate hyphae. ### 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 1

All of the following statements about thrush are true EXCEPT?

Accepted Answer

It is caused by a gram-negative fungus

Answer

It is characterized by a plaque of proliferating epithelial and other cells

Answer

It is a complication of immunosuppression or systemic disease

Answer

It can affect neonates in an epidemic fashion

Question 2

Which of the following is NOT a characteristic of Cryptococcus neoformans?

Accepted Answer

A non-encapsulated fungus that infects humans

Answer

Causes meningitis

Answer

Melanin production is related to virulence

Answer

A basidiomycetes yeast

Question 3

White piedra is caused by which of the following fungi?

Accepted Answer

Trichosporon beigelii

Answer

Piedraia hortae

Answer

Malassezia globosa

Answer

Hortaea werneckii

Question 4

All of the following are true about Candida EXCEPT:

Accepted Answer

It is a mould

Answer

Pseudohyphae are seen

Answer

It produces chlamydospores

Answer

It is a non-thermally dimorphic fungus

Question 5

Which fungus is typically not isolated in standard culture media?

Accepted Answer

Pneumocystis jiroveci

Answer

Cryptococcus

Answer

Dermatophyte

Answer

Candida

Question 6

Which statement is NOT true about Cryptococcus neoformans?

Accepted Answer

Is urease negative

Answer

Grows at 37°C

Answer

Grows on Sabouraud's agar

Answer

Has a polysaccharide capsule

Question 7

A HIV positive patient presents with cough for 10 days. Sputum culture by SDA reveals broad budding yeast. What is the diagnosis?

Accepted Answer

Blastomycosis

Answer

Histoplasma capsulatum

Answer

Coccidiodomycosis

Answer

Paracoccidiomycosis

Question 8

A patient suffering from AIDS presents with a history of dyspnea and non-productive cough. X-ray shows bilateral perihilar opacities without pleural effusion and lymphadenopathy. What is the most probable etiological agent?

Accepted Answer

Pneumocystis jirovecii

Answer

Tuberculosis

Answer

CMV

Answer

Kaposi's sarcoma

Question 9

Tinea pedis is caused by which of the following?

Accepted Answer

E. floccosum

Answer

M. furfur

Answer

M. canis

Answer

E. werneckii

Question 10

Which type of hyphae is characteristic of Aspergilloma?

Accepted Answer

Septate hyphae

Answer

Pseudohyphae

Answer

Metachromatic hyphae

Answer

No hyphae

Mycology — MCQs

Mycology — MCQs

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