Mycology Practice Questions

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.

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.

Question 1

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 2

Which fungus is typically not isolated in standard culture media?

Accepted Answer

Pneumocystis jiroveci

Answer

Cryptococcus

Answer

Dermatophyte

Answer

Candida

Question 3

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 4

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 5

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 6

Tinea pedis is caused by which of the following?

Accepted Answer

E. floccosum

Answer

M. furfur

Answer

M. canis

Answer

E. werneckii

Question 7

Which type of hyphae is characteristic of Aspergilloma?

Accepted Answer

Septate hyphae

Answer

Pseudohyphae

Answer

Metachromatic hyphae

Answer

No hyphae

Question 8

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 9

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 10

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

Mycology — MCQs

Mycology — MCQs

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