Mycology Practice Questions

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.

Q: A 39-year-old patient with HIV and a CD4 count of 139 cells/μL presents with altered sensorium and impaired consciousness. CSF examination using an India ink preparation reveals a positive result. Which organism is most likely responsible?

Cryptococcus neoformans. ***Cryptococcus neoformans***- The classic finding of a positive **India ink preparation** upon CSF examination indicates the large polysaccharide **capsule** characteristic of this yeast.- In patients with advanced HIV (**CD4 <200** cells/μL), *C. neoformans* is the most common cause of **fungal meningoencephalitis** presenting with altered mental status.*Aspergillus fumigatus*- CNS infection with *Aspergillus* usually manifests as **focal cerebral lesions** (abscesses) or hemorrhagic infarction due to angioinvasion, not typically diffuse meningitis.- Diagnosis generally relies on culturing the fungus, **histopathology** showing septate hyphae, or detecting **galactomannan antigen** in the serum or CSF.*Histoplasma capsulatum*- While it can cause disseminated infection in patients with AIDS, CNS involvement is less frequent than *Cryptococcus* and the yeast is **intracellular** (within macrophages).- Detection typically utilizes **Histoplasma antigen testing** in urine or serum, as the small yeasts do not possess the large capsule highlighted by India ink.*Candida albicans*- *Candida* is a common cause of superficial or disseminated infection, but isolated **Candida meningitis** is rare, usually seen after neurosurgery or hematogenous seeding.- *Candida* **lacks the prominent capsule** that would produce a positive result on an India ink preparation.

Q: Which of the following is least likely to cause mucormycosis?

Broad spectrum antibiotics. ***Broad spectrum antibiotics*** - While broad-spectrum antibiotics predispose to many fungal infections (especially *Candida* infections) by disrupting the normal **microbiome**, they are not typically considered a direct, primary risk factor for **mucormycosis** [1]. - *Mucorales* are ubiquitous molds, and their pathogenicity is primarily related to defects in **phagocytic function** (like in neutropenia) [2] or **acidosis/iron overload** (like in DKA), not bacterial flora changes [2]. *Neutropenia* - Profound **neutropenia** (low neutrophil count) significantly impairs the host's ability to clear fungal spores, making it one of the most important risk factors for invasive mold infections, including **mucormycosis** [2]. - Neutrophils are crucial for the primary defense against **Mucorales** by killing the spores and hyphae. *Uncontrolled diabetes without DKA* - Even without **diabetic ketoacidosis (DKA)**, poorly controlled diabetes leads to impaired phagocyte function and immunosuppression, increasing the risk of invasive fungal infections like *Mucorales* and **Candida** [2], [3]. - The high glucose environment, especially in the **nasal mucosa**, can facilitate the growth and invasion of these fungi. *Prolonged use of steroid* - Glucocorticoids cause generalized **immunosuppression** by impairing the function of phagocytes and T-lymphocytes, thereby increasing susceptibility to opportunistic infections [3]. - High-dose or prolonged corticosteroid use is a well-established risk factor for severe and disseminated **mucormycosis** as it compromises the innate immune response.

Q: Which of the following dimorphic fungi causes subcutaneous mycosis?

Sporothrix schenckii. ***Sporothrix schenckii***- This dimorphic fungus is the classic causative agent of **sporotrichosis**, which is classified as a **subcutaneous mycosis** associated with inoculation injuries (e.g., from roses or hay).- Infection often presents as a primary skin lesion followed by characteristic **lymphocutaneous spread** along lymphatic channels.*Histoplasma capsulatum*- It causes **histoplasmosis**, which is primarily classified as a **systemic or deep mycosis** that is acquired by inhaling microconidia from bird or bat droppings.- Although dissemination can occur, it is not categorized as a primary subcutaneous mycosis initiated by direct wound inoculation.*Blastomyces dermatitidis*- This fungus causes **blastomycosis**, which is considered a **systemic mycosis** primarily affecting the lungs following inhalation of spores.- While disseminated disease frequently involves the skin, causing sharply demarcated verrucous lesions, the infection route remains systemic rather than purely subcutaneous.*Penicilliosis marneffei*- Now known as *Talaromyces marneffei*, it causes **talaromycosis**, which is an **opportunistic systemic mycosis** predominantly affecting immunocompromised individuals in Southeast Asia.- Though it causes diverse skin manifestations (e.g., papules, nodules), the overall clinical picture is one of deep, disseminated infection, not a localized subcutaneous mycosis like sporotrichosis.

Question 1

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 2

What is the causative agent of Favus?

Accepted Answer

Tinea schoenleinii

Answer

Tinea rubrum

Answer

Malassezia furfur

Answer

Epidermophyton floccosum

Question 3

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 4

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 5

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 6

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 7

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

Question 8

A 39-year-old patient with HIV and a CD4 count of 139 cells/μL presents with altered sensorium and impaired consciousness. CSF examination using an India ink preparation reveals a positive result. Which organism is most likely responsible?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Histoplasma capsulatum

Answer

Aspergillus fumigatus

Question 9

Which of the following is least likely to cause mucormycosis?

Accepted Answer

Broad spectrum antibiotics

Answer

Neutropenia

Answer

Uncontrolled diabetes without DKA

Answer

Prolonged use of steroid

Question 10

Which of the following dimorphic fungi causes subcutaneous mycosis?

Accepted Answer

Sporothrix schenckii

Answer

Blastomyces dermatitidis

Answer

Penicilliosis marneffei

Answer

Histoplasma capsulatum

Mycology — MCQs

Mycology — MCQs

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