Mycology Practice Questions

Q: A 63-year-old man with insulin-dependent diabetes develops a black, crusting lesion in the nose and left maxillary sinus. Biopsy reveals nonseptate hyphae. What is the diagnosis?

Mucor mycosis. **Explanation:** The clinical presentation of a **black, crusting lesion** (eschar) in the nasal cavity and maxillary sinus of an **uncontrolled diabetic patient** is a classic hallmark of **Rhinocerebral Mucormycosis**. **Why Mucormycosis is correct:** Mucormycosis is an opportunistic fungal infection caused by fungi of the order Mucorales. It predominantly affects immunocompromised individuals, especially those with **Diabetic Ketoacidosis (DKA)** or poorly controlled diabetes. The fungus thrives in acidic, glucose-rich environments. The definitive histopathological finding is the presence of **broad, non-septate hyphae** that branch at **right angles (90°)**. These fungi are angioinvasive, leading to tissue infarction and the characteristic black necrotic eschar. **Why other options are incorrect:** * **Erysipelas:** A superficial bacterial skin infection (usually *S. pyogenes*) characterized by a well-demarcated, raised, erythematous rash. It does not present with non-septate hyphae or deep sinus involvement. * **Eczema:** An inflammatory skin condition (atopic dermatitis) presenting with pruritus and vesicles; it is not an invasive fungal infection. * **Scarlet fever:** A systemic bacterial infection caused by Group A Streptococcus, characterized by a "sandpaper" rash and "strawberry tongue," not necrotic sinus lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factor:** Uncontrolled Diabetes (DKA) is the most common association. * **Microscopy:** Broad, ribbon-like, **non-septate** hyphae with **90-degree (right-angle)** branching. (Contrast with *Aspergillus*: Septate hyphae with 45-degree branching). * **Treatment:** Immediate surgical debridement + Intravenous **Liposomal Amphotericin B**. * **Complication:** Can spread rapidly to the orbit (proptosis) and brain (cavernous sinus thrombosis).

Q: Which of the following represents a dimorphic fungus causing subcutaneous mycosis?

Sporotrichosis. **Explanation:** The correct answer is **Sporotrichosis** (*Sporothrix schenckii*). To answer this question correctly, one must distinguish between the classification of fungi based on the **site of infection** and their **morphological characteristics**. **1. Why Sporotrichosis is correct:** * **Classification:** It is the classic example of a **subcutaneous mycosis**. * **Dimorphism:** It is a **thermally dimorphic** fungus. At room temperature (25°C), it exists in a mold form (septate hyphae with "rosette-like" conidia), and at body temperature (37°C), it exists as a pleomorphic yeast (often described as **cigar-shaped bodies**). * **Clinical Context:** It typically follows traumatic inoculation (e.g., a thorn prick), leading to "Rose Gardener’s Disease," characterized by linear nodules along lymphatic channels (lymphocutaneous spread). **2. Why other options are incorrect:** * **Histoplasmosis (A) & Blastomycosis (D):** While both are thermally dimorphic, they are classified as **Systemic Mycoses**. They primarily cause pulmonary infections via inhalation of spores rather than subcutaneous infections via inoculation. * **Rhinosporidiosis (B):** Caused by *Rhinosporidium seeberi*, it affects mucous membranes (nose/eyes) and is classified as a subcutaneous mycosis. However, it is **not dimorphic**; it is currently classified as a Mesomycetozoea (a protist-like parasite) and produces characteristic sporangia containing endospores. **NEET-PG High-Yield Pearls:** * **Asteroid Bodies:** Often seen in sporotrichosis (Splendore-Hoeppli phenomenon). * **Drug of Choice:** Oral **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. * **Culture:** On Sabouraud Dextrose Agar (SDA), *Sporothrix* produces moist, wrinkled colonies that turn black over time.

Q: Pneumocystis carinii typically infects which host?

Rat. **Explanation:** The nomenclature of *Pneumocystis* species has undergone significant revision based on genetic analysis. The organism originally named ***Pneumocystis carinii*** is now recognized as a species that specifically infects **rats**. The species that causes human infection (Pneumocystis pneumonia or PCP) is now formally named ***Pneumocystis jirovecii***. This distinction is critical for NEET-PG, as the organism exhibits strict **host-species specificity**, meaning the species infecting one animal cannot infect another. **Analysis of Options:** * **C. Rat (Correct):** *P. carinii* is the specific name reserved for the strain found in rats. It was the first species described and was long used as a blanket term for all *Pneumocystis* infections before DNA sequencing proved host specificity. * **A. Human:** Humans are infected by ***P. jirovecii***. While older textbooks may use the term *P. carinii* interchangeably, modern medical exams differentiate them. * **B. Monkey:** Monkeys are infected by *P. oryctolagi* or other host-specific strains, not *P. carinii*. * **D. Cats:** Similarly, cats have their own specific strains of *Pneumocystis*. **High-Yield Clinical Pearls for NEET-PG:** * **Taxonomy:** Formerly classified as a protozoan, *Pneumocystis* is now classified as a **fungus** based on nucleic acid analysis (rRNA). * **Staining:** The gold standard for diagnosis is the **Gomori Methenamine Silver (GMS)** stain, which reveals "crushed ping-pong ball" or "cup-shaped" cysts. * **Clinical Marker:** Elevated **Beta-D-Glucan** levels in the serum are a sensitive (though non-specific) marker for PCP. * **Treatment:** The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, not traditional antifungals like Amphotericin B, because *Pneumocystis* lacks ergosterol in its cell membrane.

Q: Inhalation of fungal spores can cause primary lung infections. Which of the following organisms is most likely to be associated with this mode of transmission?

Coccidioides immitis. **Explanation:** **1. Why Coccidioides immitis is correct:** *Coccidioides immitis* is a **dimorphic fungus** endemic to the Southwestern United States and parts of Central/South America. It follows a respiratory mode of transmission: arthroconidia (spores) found in soil become airborne when the ground is disturbed. Upon **inhalation**, these spores reach the alveoli and transform into spherules containing endospores, leading to primary pulmonary coccidioidomycosis (Valley Fever). This aligns with the classic presentation of systemic/endemic mycoses which primarily affect the lungs. **2. Why the other options are incorrect:** * **Sporothrix schenckii:** This is a subcutaneous fungus. Transmission typically occurs via **traumatic inoculation** (e.g., a rose thorn prick), leading to "Rose Gardener’s Disease" (lymphocutaneous sporotrichosis). * **Candida albicans:** This is an **opportunistic yeast** that is part of the normal human flora (commensal). Infections are usually endogenous (due to overgrowth) rather than acquired via inhalation of environmental spores. * **Trichophyton tonsurans:** This is a **dermatophyte** that causes superficial infections (Tinea capitis). Transmission occurs through direct contact with infected persons or fomites (combs, hats), not inhalation. **High-Yield Clinical Pearls for NEET-PG:** * **Dimorphic Fungi Mnemonic:** "Body Heat is Probably Great" (**B**lastomyces, **H**istoplasma, **P**aracoccidioides, **G**eotrichum/Coccidioides/Sporothrix). * **Coccidioides Morphology:** In tissue, look for **thick-walled spherules filled with endospores** (Pathognomonic). * **Risk Factors:** Dust storms, earthquakes, or construction in endemic areas increase the risk of spore inhalation. * **Erythema Nodosum:** Often seen as a hypersensitivity reaction in primary Coccidioidomycosis, indicating a good prognosis.

Q: What is the causative agent of Favus?

Tinea schoenleinii. **Explanation:** **Favus** (Tinea favosa) is a chronic inflammatory form of Tinea capitis characterized by the presence of **scutula**—yellow, cup-shaped crusts composed of hyphae and keratin debris. 1. **Why Option A is Correct:** **Trichophyton schoenleinii** is the primary causative agent of Favus. It is an anthropophilic fungus that causes a unique pattern of hair infection where hyphae and air bubbles are seen inside the hair shaft (endothrix), but the hair does not always break, leading to long-term infection and permanent **cicatricial (scarring) alopecia**. A characteristic "mousy odor" is often associated with the scalp crusts. 2. **Why the Other Options are Incorrect:** * **B. Trichophyton rubrum:** This is the most common cause of dermatophytosis worldwide (Tinea corporis, pedis, and unguium) but rarely causes Favus or Tinea capitis. * **C. Malassezia furfur:** This is a yeast responsible for **Pityriasis versicolor** and Seborrheic dermatitis, not dermatophyte infections like Favus. * **D. Epidermophyton floccosum:** This dermatophyte commonly causes Tinea cruris and Tinea pedis. Notably, it **never infects hair**, making it an impossible cause for Favus. **NEET-PG High-Yield Pearls:** * **Clinical Triad of Favus:** Scutula, mousy odor, and scarring alopecia. * **Microscopy:** Look for **"Favic chandeliers"** (antler-like hyphae) on culture and air bubbles within the hair shaft on KOH mount. * **Wood’s Lamp:** T. schoenleinii shows a characteristic **dull green fluorescence**. * **Epidermophyton rule:** Remember that *Epidermophyton* species infect skin and nails, but **never hair**.

Q: Budding reproduction in tissue is seen in which of the following?

Cryptococcus, Candida. **Explanation:** The question tests the ability to distinguish between different morphological forms of fungi in clinical specimens (tissue). **1. Why Option A is Correct:** Budding is the characteristic asexual reproduction method of **yeasts**. * **Cryptococcus neoformans:** Exists strictly as a yeast. In tissue, it appears as circular, budding cells surrounded by a thick polysaccharide capsule (visualized with India Ink or Mucicarmine). * **Candida albicans:** Is a polymorphic fungus. In tissue, it typically shows **budding yeast cells (blastoconidia)** along with pseudohyphae and true hyphae. **2. Why Other Options are Incorrect:** * **Rhizopus and Mucor (Options B & C):** These belong to the class Zygomycetes. They do not bud; instead, they exist as **molds** characterized by broad, **aseptate hyphae** with right-angle (90°) branching. * **Histoplasma (Option D):** While *Histoplasma capsulatum* is a dimorphic fungus that exists as a small intracellular budding yeast in tissue, Option A is a "more correct" or classic pair in many standard textbooks when discussing general budding characteristics in clinical samples. However, in many competitive contexts, the presence of **Rhizopus/Mucor** (which are non-budding) automatically invalidates options B and C. **3. NEET-PG High-Yield Pearls:** * **Cryptococcus:** Look for "Narrow-based budding." It is the only medically important fungus with a prominent capsule. * **Candida:** Look for "Pseudohyphae" (sausage-like chains) and "Germ tube" positivity. * **Zygomycosis (Mucor/Rhizopus):** Associated with uncontrolled Diabetes (Ketoacidosis) and shows angioinvasion. * **Histoplasma:** Often described as "Small yeasts within macrophages" (resembling *Leishmania* but with a nucleus and no kinetoplast).

Q: An AIDS-positive patient came with a history of fever, vomiting, and meningismus. Which of the following tests help in the rapid diagnosis of cryptococcal meningitis?

Urine lateral flow assay for cryptococcal antigen. ***Urine lateral flow assay for cryptococcal antigen*** - The **Cryptococcal Antigen (CrAg) lateral flow assay (LFA)**, performed on various body fluids (CSF, serum, or urine), allows for rapid diagnosis, often yielding results in 10 minutes. - Detection of CrAg is highly sensitive in patients with extensive disease, such as those with AIDS and high fungal burdens, facilitating quick initiation of life-saving antifungal therapy. *India ink preparation of CSF* - Although relatively quick, the **India ink preparation** has low sensitivity (50-75%) in HIV-associated cryptococcal meningitis, leading to potential false-negative results. - This test identifies the yeast by visualizing the characteristic **capsule** against a black background, but its utility has largely been replaced by the more sensitive CrAg assay. *Blood culture* - Blood cultures confirm **cryptococcemia** (disseminated infection), which is common in AIDS patients with meningitis, but require several days (3–7 or more) for growth and identification. - Due to the prolonged incubation time, blood culture is unsuitable for the **rapid diagnosis** required to manage acute meningeal symptoms promptly. *CSF culture* - CSF culture remains the **gold standard** for definitive diagnosis, confirmation of viability, and performance of antifungal susceptibility testing. - Similar to blood culture, CSF culture takes multiple days (typically 2–7 days) to provide results, thus delaying immediate treatment needed for **meningitis**.

Q: Identify the opportunistic pathogen demonstrating a 'crushed ping pong ball appearance' on Gomori methenamine stain shown in the image.

Pneumocystis jirovecii. ***Pneumocystis jirovecii*** - The image displays cysts stained with **Gomori methenamine silver (GMS)**, showing the classic **'crushed ping pong ball'** or crescent-shaped appearance, which is pathognomonic for *Pneumocystis jirovecii*. - This organism is a well-known opportunistic fungus that causes **Pneumocystis pneumonia (PCP)**, particularly in immunocompromised individuals, such as those with HIV/AIDS. *Histoplasma capsulatum* - On staining, *Histoplasma capsulatum* appears as small, oval, budding yeasts, often found intracellularly within **macrophages**. - It does not form the larger, often collapsed, cystic structures seen in the image. *Cryptococcus neoformans* - This is an encapsulated yeast, classically identified by the prominent halo seen with an **India ink stain** due to its thick **polysaccharide capsule**. - While it stains with GMS, it appears as budding yeasts of varying sizes and does not have a crushed appearance. *Aspergillus fumigatus* - *Aspergillus* is a mold characterized by **septate hyphae** that branch at **acute angles** (approximately 45 degrees) in tissue specimens. - It does not exist in a cystic form like that shown in the image.

Q: Which opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?

Pneumocystis jirovecii. ***Pneumocystis jirovecii*** - This opportunistic fungus classically appears as collapsed, crescent-shaped cysts on **Gomori methenamine silver (GMS) stain**, giving it the pathognomonic **“crushed ping pong ball”** appearance. - It is a common cause of **Pneumocystis pneumonia (PCP)** in immunocompromised individuals, particularly those with advanced HIV infection, and is typically found in the alveolar spaces. *Histoplasma capsulatum* - This dimorphic fungus appears as small, oval yeasts that are characteristically found **intracellularly within macrophages**. - It does not form the collapsed cysts seen with *P. jirovecii* and lacks the “crushed ping pong ball” morphology. *Cryptococcus neoformans* - This yeast is distinguished by its thick **polysaccharide capsule**, which creates a clear halo around the organism on **India ink stain**. - While it can be stained with GMS, it appears as a budding yeast and does not exhibit the collapsed cyst morphology. *Aspergillus fumigatus* - This mold is identified by its characteristic **septate hyphae** that branch at **acute (45-degree) angles**. - It does not form cysts in tissue and has a filamentous structure, which is entirely different from the appearance of *P. jirovecii*.

Q: A person came with the H/o thorn prick a week ago. A few days later, he developed ulcers along lymphatic drainage. Choose the correct organism.

Sporothrix schenckii. ***Sporothrix schenckii*** - This dimorphic fungus is introduced via cutaneous trauma, classically associated with exposure to vegetation (e.g., **thorn prick**, sphagnum moss), leading to the term **Gardener's disease**. - The characteristic presentation of a primary nodule followed by secondary subcutaneous nodules or ulcers tracking along the proximal lymphatic drainage is diagnostic of **lymphocutaneous sporotrichosis**. *Coccidioides immitis* - This fungus causes **Coccidioidomycosis** (Valley fever), generally acquired by inhaling arthroconidia, leading primarily to pulmonary infection. - While disseminated infection can involve the skin, it does not typically present as a localized inoculation lesion with subsequent **ascending lymphangitis** from a thorn prick. *Aspergillus flavus* - **Aspergillus** species usually cause infections in immunocompromised patients (e.g., invasive pulmonary aspergillosis) or superficial infections such as fungal keratitis. - It is not the organism characteristically associated with traumatic inoculation from plant material causing a **sporotrichoid pattern** of lymphatic spread. *Trichophyton rubrum* - This is a common **dermatophyte** that causes superficial cutaneous infections of the keratin layer, such as tinea (ringworm) of the skin, hair, or nails. - It lacks the invasive capability to establish a deep infection followed by **lymphatic involvement** and ulceration after subcutaneous inoculation.

Question 1

A 63-year-old man with insulin-dependent diabetes develops a black, crusting lesion in the nose and left maxillary sinus. Biopsy reveals nonseptate hyphae. What is the diagnosis?

Accepted Answer

Mucor mycosis

Answer

Erysipelas

Answer

Eczema

Answer

Scarlet fever

Question 2

Which of the following represents a dimorphic fungus causing subcutaneous mycosis?

Accepted Answer

Sporotrichosis

Answer

Histoplasmosis

Answer

Rhinosporidiosis

Answer

Blastomycosis

Question 3

Pneumocystis carinii typically infects which host?

Accepted Answer

Rat

Answer

Human

Answer

Monkey

Answer

Cats

Question 4

Inhalation of fungal spores can cause primary lung infections. Which of the following organisms is most likely to be associated with this mode of transmission?

Accepted Answer

Coccidioides immitis

Answer

Sporothrix schenckii

Answer

Candida albicans

Answer

Trichophyton tonsurans

Question 5

What is the causative agent of Favus?

Accepted Answer

Tinea schoenleinii

Answer

Tinea rubrum

Answer

Malassezia furfur

Answer

Epidermophyton floccosum

Question 6

Budding reproduction in tissue is seen in which of the following?

Accepted Answer

Cryptococcus, Candida

Answer

Candida, Rhizopus

Answer

Rhizopus, Mucor

Answer

Histoplasma, Candida

Question 7

An AIDS-positive patient came with a history of fever, vomiting, and meningismus. Which of the following tests help in the rapid diagnosis of cryptococcal meningitis?

Accepted Answer

Urine lateral flow assay for cryptococcal antigen

Answer

CSF culture

Answer

India ink preparation of CSF

Answer

Blood culture

Question 8

Identify the opportunistic pathogen demonstrating a 'crushed ping pong ball appearance' on Gomori methenamine stain shown in the image.

Accepted Answer

Pneumocystis jirovecii

Answer

Cryptococcus neoformans

Answer

Histoplasma capsulatum

Answer

Aspergillus fumigatus

Question 9

Which opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?

Accepted Answer

Pneumocystis jirovecii

Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Histoplasma capsulatum

Question 10

A person came with the H/o thorn prick a week ago. A few days later, he developed ulcers along lymphatic drainage. Choose the correct organism.

Accepted Answer

Sporothrix schenckii

Answer

Trichophyton rubrum

Answer

Coccidioides immitis

Answer

Aspergillus flavus

Mycology — MCQs

Mycology — MCQs

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