Mycology Practice Questions

Q: Which organism is known to be capsulated?

Cryptococcus neoformans. **Explanation:** The correct answer is **Cryptococcus neoformans**. In microbiology, the capsule is a major virulence factor that inhibits phagocytosis. While many bacteria are capsulated, *Cryptococcus neoformans* is the **only medically important fungus** that possesses a prominent polysaccharide (glucuronoxylomannan) capsule. **Why the other options are incorrect:** * **Histoplasma capsulatum:** Despite its misleading name, this fungus is **not capsulated**. The name "capsulatum" was given by its discoverer, Samuel Darling, who mistakenly identified the halo around the yeast cells in tissue sections (an artifact of shrinkage) as a capsule. * **Neisseria gonorrhoeae:** Unlike its relative *Neisseria meningitidis* (which is heavily capsulated), *N. gonorrhoeae* is **non-capsulated**. It relies on pili and Opa proteins for virulence and attachment. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** The capsule of *Cryptococcus* is best visualized using **India Ink** or **Nigrosin** (negative staining), where it appears as a clear halo against a dark background. * **Biochemical Marker:** For tissue sections, **Mucicarmine stain** is specific for the Cryptococcal capsule (stains it bright red). * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test is a highly sensitive latex agglutination test used to detect the capsular polysaccharide in CSF or serum. * **Mnemonic for Capsulated Organisms:** "Some Killers Have Nice Shiny Bodies" (**S**trep pneumoniae, **K**lebsiella, **H**aemophilus influenzae, **N**eisseria meningitidis, **S**almonella typhi, **B**acillus anthracis—notably a polypeptide capsule).

Q: Tinea Nigra is caused by which organism?

Hortaea werneckii. **Explanation:** **Tinea Nigra** is a superficial fungal infection (superficial mycosis) characterized by asymptomatic, brown-to-black non-scaly macules, typically on the palms and soles. 1. **Why Option A is Correct:** The causative agent of Tinea Nigra is **Hortaea werneckii** (formerly known as *Exophiala werneckii*). It is a **dematiaceous** (pigmented) fungus that produces melanin, giving the clinical lesion its characteristic dark appearance. Diagnosis is confirmed by skin scrapings in KOH, which show branched, septate dark hyphae and elongated budding cells. 2. **Why Other Options are Incorrect:** * **B. Piedraia hortae:** This organism causes **Black Piedra**, a superficial infection of the hair shaft characterized by hard, black nodules. * **C. T. rubrum (Trichophyton rubrum):** This is a dermatophyte and the most common cause of Tinea corporis, Tinea pedis, and Onychomycosis. It involves deeper keratinized layers compared to Tinea Nigra. * **D. Microsporum:** This is a genus of dermatophytes that commonly causes Tinea capitis and Tinea corporis, often characterized by ectothrix hair involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Often misdiagnosed as malignant melanoma; however, Tinea Nigra is superficial and can be "scraped off." * **Transmission:** Usually occurs via traumatic inoculation from soil, sewage, or decaying vegetation. * **Culture:** On Sabouraud Dextrose Agar (SDA), it produces black, mucoid, yeast-like colonies. * **Treatment:** Topical antifungal creams (e.g., Whitfield ointment, imidazoles).

Q: Impaired immune competence is the predisposing factor in about half of all persons who develop which of the following fungal infections?

Cryptococcosis. **Explanation:** The correct answer is **Cryptococcosis**. **1. Why Cryptococcosis is correct:** *Cryptococcus neoformans* is considered a classic **opportunistic fungal pathogen**. While it can occasionally infect healthy individuals, approximately **50% to 80%** of clinically significant cases occur in patients with impaired cell-mediated immunity (CMI). The most common predisposing factor is HIV/AIDS (typically when CD4 counts are <100 cells/µL), followed by organ transplant recipients, patients on chronic corticosteroids, and those with hematological malignancies. The fungus is inhaled but requires a weakened immune system to disseminate, most commonly causing meningoencephalitis. **2. Why the other options are incorrect:** * **A, B, and C (Histoplasmosis, Coccidioidomycosis, and Blastomycosis):** These are classified as **Systemic (Endemic) Mycoses**. Unlike opportunistic fungi, these are **primary pathogens**, meaning they are inherently virulent and can cause significant disease in **immunocompetent** individuals who inhale a sufficient fungal load. While immunosuppression can lead to more severe or disseminated forms of these diseases, the majority of infections occur in healthy hosts living in endemic geographical regions. **3. NEET-PG High-Yield Pearls:** * **Source:** Pigeon droppings and contaminated soil. * **Virulence Factor:** The **Polysaccharide capsule** (inhibits phagocytosis) is the most important. * **Diagnosis:** * **India Ink:** Shows a clear halo (capsule) against a dark background. * **Culture:** Niger seed agar/Bird seed agar (produces melanin). * **Antigen Detection:** CrAg (Cryptococcal Antigen) via Lateral Flow Assay is the most sensitive screening test. * **Histopathology:** Mucicarmine stain (stains capsule red). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: Which fungus is capable of forming a fungal ball?

Aspergillus. **Explanation:** **Aspergillus** is the most common cause of a **fungal ball (Aspergilloma)**. This occurs when the fungus colonizes a pre-existing lung cavity (most commonly formed by **Tuberculosis**, but also sarcoidosis or bronchiectasis). The fungus grows as a saprophytic mass of hyphae, fibrin, and cellular debris without invading the surrounding tissue. On a chest X-ray, it presents as a mobile, gravity-dependent mass with a characteristic **"Air-crescent sign" (Monod sign)**. **Analysis of Options:** * **Aspergillus (Correct):** Specifically *Aspergillus fumigatus*. It is unique in its ability to form non-invasive balls in pulmonary cavities. * **Mucor & Rhizopus (Incorrect):** These belong to the order Mucorales. They are characterized by **angioinvasion**, leading to infarction and necrosis (e.g., Rhinocerebral mucormycosis). They do not typically form organized, non-invasive fungal balls. * **Penicillium (Incorrect):** While *Talaromyces (Penicillium) marneffei* is a significant pathogen in HIV patients, it causes disseminated intracellular infection rather than cavitary fungal balls. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** Gold standard is culture; however, the presence of **serum precipitins (IgG antibodies)** against Aspergillus is highly sensitive for Aspergilloma. 2. **Microscopy:** Aspergillus shows **septate hyphae** with **acute-angle (45°) branching**, whereas Mucorales show broad, aseptate hyphae with right-angle branching. 3. **Clinical Presentation:** The most common symptom of an Aspergilloma is **hemoptysis**, which can occasionally be life-threatening. 4. **Treatment:** Surgical resection is the definitive treatment for symptomatic cases; systemic antifungals have poor penetration into the fungal ball.

Q: Systemic infection is caused by all fungi except?

Dermatophytes. **Explanation:** The classification of fungal infections is based on the depth of tissue involvement. Fungi are categorized into superficial, cutaneous, subcutaneous, and systemic (deep) mycoses. **Why Dermatophytes is the correct answer:** Dermatophytes (genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*) cause **cutaneous mycoses**. These fungi are "keratinophilic," meaning they require keratin for growth. Since keratin is only found in the non-living cornified layers of the skin, hair, and nails, these infections remain restricted to the **superficial integument**. They lack the biochemical machinery to invade deeper tissues or survive at core body temperatures, thus they **do not cause systemic infection.** **Analysis of Incorrect Options:** * **Cryptococcus:** An encapsulated yeast (primarily *C. neoformans*) that causes systemic disease, most notably meningitis and pulmonary infections, especially in immunocompromised patients. * **Histoplasma:** A dimorphic fungus that causes systemic histoplasmosis. It is an intracellular pathogen that involves the reticuloendothelial system (lungs, liver, spleen). * **Paracoccidioides:** A dimorphic fungus causing Paracoccidioidomycosis, a systemic infection prevalent in South America that affects the lungs and mucous membranes. **NEET-PG High-Yield Pearls:** * **Systemic Mycoses** are typically caused by dimorphic fungi (except *Cryptococcus*, which is a yeast). * **Dermatophytes** are diagnosed using KOH mounts showing branching hyphae and are treated with topical antifungals or oral Griseofulvin/Terbinafine. * **Wood’s Lamp:** Used to detect certain *Microsporum* species (fluoresce bright green). * **Culture Media:** Sabouraud Dextrose Agar (SDA) is the standard medium for most fungi.

Q: Draining sinuses are seen in which of the following conditions?

Mycetoma. **Explanation:** **Mycetoma** is a chronic, granulomatous infection of the skin and subcutaneous tissue, most commonly affecting the foot (Madura foot). The classic clinical triad of Mycetoma consists of: 1. **Localized swelling** (Tumefaction) 2. **Multiple interconnecting draining sinuses** 3. **Presence of grains** (sulfur-like granules) in the discharge. It is caused by either fungi (**Eumycetoma**) or filamentous bacteria (**Actinomycetoma**). The sinuses serve as channels for the body to discharge these colonial grains. **Analysis of Incorrect Options:** * **Scrofula:** This is tuberculous cervical lymphadenitis. While it can lead to "cold abscesses" that may eventually rupture to form sinuses, it is primarily a lymph node pathology rather than a primary subcutaneous infection characterized by the classic draining sinus triad. * **Lupus Vulgaris:** A progressive form of cutaneous tuberculosis characterized by "apple-jelly nodules" on diascopy. It typically presents as plaques or ulcers rather than deep draining sinuses. * **Pediculosis:** This refers to infestation with lice (head, body, or pubic). It presents with pruritus and excoriations, not deep tissue destruction or sinus formation. **High-Yield Clinical Pearls for NEET-PG:** * **Eumycetoma:** Most common cause worldwide is *Madurella mycetomatis*. Grains are usually black or white. * **Actinomycetoma:** Most common cause in India is *Nocardia brasiliensis* or *Actinomadura madurae*. Grains are usually white, yellow, or red. * **Diagnosis:** Crushing the grains and performing Gram stain/KOH mount is the initial step. * **Dot-in-a-circle sign:** A characteristic MRI finding in Mycetoma where the "dot" represents the grain and the "circle" represents the inflammatory granuloma.

Q: A patient with a previous history of tuberculosis complains of hemoptysis. Chest x-ray reveals an upper lobe mass with a cavity and a crescent-shaped air-fluid level. What is the most likely etiologic agent?

Aspergillus flavus. ### Explanation **Correct Answer: A. Aspergillus flavus** The clinical presentation describes a classic **Aspergilloma** (fungus ball). This occurs when *Aspergillus* species (most commonly *A. fumigatus*, but also *A. flavus*) colonize a pre-existing pulmonary cavity, typically left behind by **Tuberculosis**, sarcoidosis, or bronchiectasis [1]. The pathognomonic radiological sign described is the **Monod sign** (a crescent-shaped air space surrounding a mobile mass within a cavity) [1]. Hemoptysis is the most common clinical symptom due to the erosion of bronchial vessels by the fungus or its metabolic products [3]. **Why the other options are incorrect:** * **B. Coccidioides immitis:** While it can cause thin-walled cavities (coccidioidomycosis), it typically presents with "Valley Fever" symptoms (fever, arthralgia, erythema nodosum) and does not characteristically form a mobile intracavitary fungus ball with a crescent sign. * **C & D. Herpes Simplex Virus (HSV-1 & 2):** These are viral pathogens. HSV-1 can cause necrotizing pneumonia in immunocompromised patients, but it does not present as a chronic intracavitary mass or "fungus ball." **NEET-PG High-Yield Pearls:** * **Air-Crescent Sign:** Also seen in the recovery phase of **Invasive Pulmonary Aspergillosis** (IPA) as necrotic lung tissue separates from healthy parenchyma; however, in a stable patient with a history of TB, it signifies an Aspergilloma [2]. * **Diagnosis:** Sputum culture is often negative; diagnosis is confirmed via **Aspergillus IgG antibodies (precipitins)** and imaging. * **Treatment:** Aspergillomas are relatively resistant to systemic antifungals. **Surgical resection** is the treatment of choice for symptomatic patients (massive hemoptysis). Bronchial Artery Embolization (BAE) is used for acute management of life-threatening bleeding.

Q: In an AIDS patient presenting with fever and cough, a diagnosis of Pneumocystis jirovecii pneumonia is best established by?

Bronchoalveolar lavage. **Explanation:** *Pneumocystis jirovecii* is an opportunistic fungus that primarily colonizes the alveolar spaces. In AIDS patients, it causes severe interstitial pneumonia (PCP). **Why Bronchoalveolar Lavage (BAL) is the correct answer:** BAL is considered the **gold standard diagnostic procedure** for PCP because it provides the highest diagnostic yield (90–95%). Since the organism resides deep within the alveoli, washing the alveolar spaces allows for the collection of a high concentration of trophozoites and cysts, which can then be identified via microscopy. **Analysis of Incorrect Options:** * **A. Transtracheal biopsy:** While highly sensitive, it is an invasive procedure with a high risk of complications like pneumothorax and hemorrhage. It is reserved only when non-invasive methods fail. * **C. Staining for Pneumocystis cysts:** This is a **method of identification**, not a method of specimen collection. While silver stains (Gomori Methenamine Silver) are used to visualize the organism, the question asks how the diagnosis is *best established* (implying the procedure/specimen). * **D. Sputum aspiration and culture:** *P. jirovecii* **cannot be cultured** on routine laboratory media. Furthermore, spontaneous sputum has a very low yield; induced sputum (using hypertonic saline) is preferred as an initial non-invasive step, but BAL remains superior. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Trimethoprim-Sulfamethoxazole (Cotrimoxazole). * **Radiology:** Characterized by bilateral "ground-glass opacities" or perihilar infiltrates. * **Microscopy:** Look for "crushed ping-pong ball" appearance of cysts on GMS stain or "cup-shaped" organisms. * **Serum Marker:** Elevated **(1,3)-beta-D-glucan** levels are highly suggestive of PCP in the right clinical context.

Question 1

Which organism is known to be capsulated?

Accepted Answer

Cryptococcus neoformans

Answer

Histoplasma capsulatum

Answer

Neisseria gonorrhoeae

Answer

All the above

Question 2

Tinea Nigra is caused by which organism?

Accepted Answer

Hortaea werneckii

Answer

Piedrae hortae

Answer

T. rubrum

Answer

Microsporum

Question 3

A 56-year-old man undergoing chemotherapy for leukemia develops fever, nonproductive cough, dyspnea, pleuritic chest pain, and hemoptysis over one week. A chest CT scan shows multiple 1- to 4-cm nodular densities with surrounding ground-glass infiltrate (halo sign). Bronchoalveolar lavage fluid microscopy reveals narrow branching septate hyphae. His CBC shows Hgb, 13 g/dL; Hct, 38.7%; WBC count, 2000/mL; and platelet count, 200,100/mL. Which of the following organisms is the most likely cause of this infection?

Accepted Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Cryptococcus neoformans

Answer

Moraxella catarrhalis

Question 4

Impaired immune competence is the predisposing factor in about half of all persons who develop which of the following fungal infections?

Accepted Answer

Cryptococcosis

Answer

Histoplasmosis

Answer

Coccidoidomycosis

Answer

Blastomycosis

Question 5

Which fungus is capable of forming a fungal ball?

Accepted Answer

Aspergillus

Answer

Penicillium

Answer

Mucor

Answer

Rhizopus

Question 6

Systemic infection is caused by all fungi except?

Accepted Answer

Dermatophytes

Answer

Cryptococcus

Answer

Histoplasma

Answer

Paracoccidioides

Question 7

Giemsa stain of yeast cells in HIV is associated with which of the following infections?

Accepted Answer

Cryptococcosis

Answer

Aspergillosis

Answer

Blastomycosis

Answer

Histoplasmosis

Question 8

Draining sinuses are seen in which of the following conditions?

Accepted Answer

Mycetoma

Answer

Scrofula

Answer

Lupus vulgaris

Answer

Pediculosis

Question 9

A patient with a previous history of tuberculosis complains of hemoptysis. Chest x-ray reveals an upper lobe mass with a cavity and a crescent-shaped air-fluid level. What is the most likely etiologic agent?

Accepted Answer

Aspergillus flavus

Answer

Coccidioides immitis

Answer

Herpes simplex virus type 1

Answer

Herpes simplex virus type 2

Question 10

In an AIDS patient presenting with fever and cough, a diagnosis of Pneumocystis jirovecii pneumonia is best established by?

Accepted Answer

Bronchoalveolar lavage

Answer

Transtracheal biopsy

Answer

Staining for Pneumocystis cysts (e.g., silver stain)

Answer

Sputum aspiration and culture

Mycology — MCQs

Mycology — MCQs

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