Mycology Practice Questions

Q: A diabetic patient with orbital cellulitis and maxillary sinusitis shows hyaline, narrow, septate, and branching hyphae with invasion of blood vessels on microscopy. Which is the causative fungus?

Aspergillus. **Explanation:** The clinical presentation of orbital cellulitis and sinusitis in a diabetic patient, combined with the specific microscopic findings, points directly to **Aspergillus**. **1. Why Aspergillus is correct:** The hallmark of *Aspergillus* species in tissue sections is the presence of **hyaline (clear), narrow, septate hyphae** that exhibit **dichotomous branching at acute angles (approximately 45°)**. Like Mucormycosis, Aspergillus is **angioinvasive**, meaning it invades blood vessel walls, leading to thrombosis and tissue infarction, which explains the aggressive clinical presentation in this patient. **2. Why other options are incorrect:** * **Rhizopus (Mucormycosis):** While it also causes aggressive rhino-orbital-cerebral disease in diabetics, its morphology is distinct: it features **broad, aseptate (coenocytic) hyphae** with **right-angle (90°) branching**. * **Candida:** Typically appears as budding yeast cells and **pseudohyphae** (elongated buds with constrictions). It does not usually present as a primary invasive fungal sinusitis with branching septate hyphae. * **Histoplasma:** This is a dimorphic fungus that, in tissue, appears as small (2-4 µm) **intracellular yeast cells** within macrophages, not as invasive branching hyphae. **High-Yield NEET-PG Pearls:** * **Acute Angle (45°) + Septate:** Aspergillus. * **Right Angle (90°) + Aseptate:** Rhizopus/Mucor. * **Vessel Invasion:** Both Aspergillus and Rhizopus are angioinvasive, but the septation and branching angle are the key differentiating factors. * **Culture:** Aspergillus grows on Sabouraud Dextrose Agar (SDA) and produces characteristic "conidial heads." *Aspergillus fumigatus* is the most common species involved in invasive disease.

Q: The 'figure of 8' appearance is characteristic of which of the following fungal infections?

Blastomycosis. **Explanation:** The correct answer is **Blastomycosis**. **Blastomycosis**, caused by the dimorphic fungus *Blastomyces dermatitidis*, is characterized by large, spherical, thick-walled yeast cells (8–15 µm). The hallmark feature seen under the microscope is **broad-based budding**. When the daughter cell buds from the parent cell, the wide attachment point creates a constricted silhouette resembling a **'figure of 8'** or a 'snowman' appearance. **Analysis of Incorrect Options:** * **Paracoccidioidomycosis:** Characterized by multiple narrow-based buds attached to a single central yeast cell, giving it a **"Pilot’s wheel"** or **"Mariner’s wheel"** appearance. * **Coccidioidomycosis:** Does not exist as yeast in tissue; instead, it forms large **spherules** (20–100 µm) filled with numerous small **endospores**. * **Sporotrichosis:** Typically presents as small, **cigar-shaped** yeast cells. It is classically associated with "rose gardener’s disease" and subcutaneous nodules following a linear lymphatic distribution. **High-Yield Clinical Pearls for NEET-PG:** * **Blastomycosis:** Think "B" for **B**lastomycosis, **B**road-based budding, and **B**one involvement (common site for dissemination). * **Geographic Distribution:** Blastomycosis is endemic to the Ohio and Mississippi River valleys and the Great Lakes region. * **Staining:** Best visualized using Silver stains (GMS) or PAS stain. * **Primary Site:** Infection usually begins in the lungs after inhalation of spores but can mimic squamous cell carcinoma of the skin (pseudoepitheliomatous hyperplasia).

Q: Phycomycosis is also called?

Mucormycosis. **Explanation:** **Phycomycosis** is an older, historical term used to describe infections caused by fungi belonging to the class **Phycomycetes**. In modern medical taxonomy, these fungi (primarily the genera *Mucor*, *Rhizopus*, and *Lichtheimia*) are classified under the order **Mucorales**. Therefore, the clinical disease is now universally referred to as **Mucormycosis**. These are opportunistic, angioinvasive infections characterized by broad, aseptate hyphae branching at right angles (90°). **Analysis of Incorrect Options:** * **A. Botryomycosis:** Despite the name, this is a **chronic bacterial infection** (most commonly *Staphylococcus aureus*) that mimics a fungal infection by forming granulomatous lesions with "grains." * **B. Coccidiomycosis:** A systemic mycosis caused by the dimorphic fungus *Coccidioides immitis*, typically presenting as "Valley Fever." It is characterized by spherules containing endospores in tissue. * **C. Phytomycosis:** This is a non-standard term and is not a recognized medical synonym for Mucormycosis. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Uncontrolled Diabetes Mellitus (especially **Ketoacidosis** due to the fungus's ketoreductase enzyme), neutropenia, and iron overload (deferoxamine use). * **Clinical Presentation:** Rhinocerebral mucormycosis is the most common form, often presenting with a **black necrotic eschar** on the palate or nasal turbinates. * **Diagnosis:** KOH mount or biopsy showing **broad, ribbon-like, aseptate hyphae** with **right-angle branching**. * **Treatment:** Surgical debridement and **Liposomal Amphotericin B** (Drug of choice). Isavuconazole and Posaconazole are alternatives.

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: Vesicular lesions, indistinguishable from primary infection, which arise in other parts of the body of an allergic individual infected with Trichophyton are referred to as?

Dermatiphytids. ### Explanation **Correct Option: A. Dermatiphytids** Dermatiphytids (or **'id' reactions**) are secondary inflammatory eruptions that occur in sensitized individuals as an allergic response to a primary fungal infection (usually a dermatophyte like *Trichophyton*). * **Mechanism:** These lesions represent a **Type IV hypersensitivity reaction** to fungal antigens circulating in the blood. * **Key Feature:** The lesions are **sterile** (fungus cannot be cultured from the 'id' site) and often appear as itchy vesicles on the hands or trunk, distant from the primary site of infection (e.g., *Tinea pedis*). They resolve only when the primary focus of infection is treated. **Analysis of Incorrect Options:** * **B. Trichophytins:** This refers to the crude antigen extract derived from *Trichophyton* species used in skin testing to detect delayed-type hypersensitivity. It is a diagnostic tool, not the clinical lesion itself. * **C. Eschars:** An eschar is a dry, dark scab or falling away of dead skin, typically seen in cutaneous anthrax, scrub typhus, or certain fungal infections like Mucormycosis. It is necrotic tissue, not an allergic reaction. * **D. Carbuncles:** A carbuncle is a cluster of interconnected furuncles (boils) caused by a bacterial infection, most commonly *Staphylococcus aureus*. It involves deep suppuration of the hair follicles. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The "id" reaction is diagnosed by the triad of: a proven primary fungal focus, sterile secondary lesions, and resolution after treating the primary site. * **Common Presentation:** The most frequent presentation is a **vesicular eruption on the sides of the fingers** associated with inflammatory *Tinea pedis* (Athlete's foot). * **Dermatophytes:** Remember the three genera: *Trichophyton* (infects hair, skin, nails), *Microsporum* (hair, skin), and *Epidermophyton* (skin, nails).

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: 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: A diabetic patient presents with whitish plaques in the oral cavity. A KOH mount confirms the presence of budding yeast with pseudohyphae. Which of the following is the most appropriate culture medium for isolation of this organism?

Sabouraud Dextrose Agar (SDA). ***Sabouraud Dextrose Agar (SDA)*** - SDA is the standard mycological culture medium used for the isolation of fungi, such as the yeast **_Candida albicans_** described in the clinical scenario. - Its **low pH** and high **dextrose** concentration inhibit the growth of most bacteria, making it selective for fungi. *Chocolate agar* - This is an enriched medium containing lysed red blood cells, primarily used for cultivating fastidious bacteria like **_Haemophilus influenzae_** and **_Neisseria_** species. - It is not a selective medium for fungi and would allow the overgrowth of oral bacteria, complicating the isolation of yeast. *Thayer-Martin medium* - This is a selective agar containing antibiotics, specifically designed to isolate pathogenic **_Neisseria_** species (**_N. gonorrhoeae_** and **_N. meningitidis_**) from samples with mixed flora. - The antibiotics in this medium inhibit the growth of gram-positive bacteria, most gram-negative bacteria, and yeast, making it unsuitable for this purpose. *Loeffler's serum slope* - This is an enrichment medium used for the cultivation of **_Corynebacterium diphtheriae_**, the causative agent of diphtheria. - It promotes the development of characteristic **metachromatic granules** within the bacteria and is not used for fungal isolation.

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*.

Question 1

A diabetic patient with orbital cellulitis and maxillary sinusitis shows hyaline, narrow, septate, and branching hyphae with invasion of blood vessels on microscopy. Which is the causative fungus?

Accepted Answer

Aspergillus

Answer

Candida

Answer

Rhizopus

Answer

Histoplasma

Question 2

The 'figure of 8' appearance is characteristic of which of the following fungal infections?

Accepted Answer

Blastomycosis

Answer

Paracoccidioidomycosis

Answer

Coccidioidomycosis

Answer

Sporotrichosis

Question 3

Phycomycosis is also called?

Accepted Answer

Mucormycosis

Answer

Botryomycosis

Answer

Coccidiomycosis

Answer

Phytomycosis

Question 4

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

Accepted Answer

Sporotrichosis

Answer

Histoplasmosis

Answer

Rhinosporidiosis

Answer

Blastomycosis

Question 5

Pneumocystis carinii typically infects which host?

Accepted Answer

Rat

Answer

Human

Answer

Monkey

Answer

Cats

Question 6

Vesicular lesions, indistinguishable from primary infection, which arise in other parts of the body of an allergic individual infected with Trichophyton are referred to as?

Accepted Answer

Dermatiphytids

Answer

Trichophytins

Answer

Eschars

Answer

Carbuncles

Question 7

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 8

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 9

A diabetic patient presents with whitish plaques in the oral cavity. A KOH mount confirms the presence of budding yeast with pseudohyphae. Which of the following is the most appropriate culture medium for isolation of this organism?

Accepted Answer

Sabouraud Dextrose Agar (SDA)

Answer

Chocolate agar

Answer

Thayer-Martin medium

Answer

Loeffler's serum slope

Question 10

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

Mycology — MCQs

Mycology — MCQs

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