Mycology Practice Questions

Q: Which of the following is the MOST COMMON fungal cause of Mucormycosis?

Rhizopus oryzae. ***Rhizopus oryzae*** - This is the **most common genus and species** responsible for mucormycosis infections in humans. - It belongs to the order **Mucorales**, which are characterized by broad, non-septate hyphae with a tendency to invade blood vessels. *Candida albicans* - This fungus is a common cause of **candidiasis**, which can manifest as thrush, vaginitis, or invasive candidemia. - It does not cause mucormycosis; its cellular morphology and disease presentation are distinct. *Aspergillus fumigatus* - This is the primary causative agent of **aspergillosis**, which can range from allergic reactions to invasive forms like chronic pulmonary aspergillosis or invasive aspergillosis. - While it can cause severe fungal infections, it is morphologically distinct (septate hyphae) and does not cause mucormycosis. *Cryptococcus neoformans* - This encapsulated yeast is best known for causing **cryptococcosis**, particularly **meningoencephalitis** in immunocompromised individuals. - Its disease presentation and microscopic features (yeast with budding, prominent capsule) are entirely different from those of Mucorales.

Q: Microscopy of a corneal ulcer shows branching septate hyphae. The probable diagnosis is

Aspergillus. ***Aspergillus*** - **Branching septate hyphae** observed on microscopy are characteristic of *Aspergillus* species, which are common causes of **fungal keratitis**, especially after ocular trauma or in immunocompromised individuals. - *Aspergillus* keratitis often presents as a **corneal ulcer** with distinct borders and satellite lesions, reflecting the invasive nature of the fungus. *Candida* - *Candida* species are typically observed as **yeast cells** that may form **pseudohyphae**, rather than true septate hyphae with dichotomous branching. - While *Candida* can cause keratitis, its microscopic appearance is distinct from the branching septate hyphae described. *Histoplasma* - *Histoplasma capsulatum* is a **dimorphic fungus** that primarily causes pulmonary infections and disseminated disease, particularly in immunocompromised patients. - It is typically seen as **small intracellular yeast forms** in macrophages, not as hyphae in corneal ulcers. *Mucormycosis* - **Mucorales** (e.g., *Mucor*, *Rhizopus*) cause **mucormycosis**, characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching. - This morphology is distinctly different from the described **branching septate hyphae**, ruling out mucormycosis.

Q: Which organism is characterized by a wide polysaccharide capsule that appears as a clear halo around the yeast cell on India ink staining?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This encapsulated yeast produces a **thick polysaccharide capsule** that is the key diagnostic feature - On **India ink preparation**, the capsule appears as a **clear halo** around the yeast cell because the ink particles cannot penetrate the capsule - This is the classic microscopic identification method for **Cryptococcus neoformans** in **cerebrospinal fluid** and other clinical specimens - The capsule can also be visualized using **mucicarmine stain** (stains red) or **alcian blue** *Penicillium marneffei* - This dimorphic fungus shows **intracellular yeast forms** with characteristic **central septation** (dividing by fission) - Typically found within macrophages and does not produce a prominent capsule - The yeast forms are oval to elongated with a transverse septum *Blastomyces dermatitidis* - Characterized by **large, thick-walled yeast cells** (8-15 μm) with **broad-based budding** - The cell wall is thick and refractile but there is **no polysaccharide capsule** - Budding occurs with a wide attachment point between mother and daughter cells *Candida albicans* - Forms **budding yeast cells**, **pseudohyphae**, and **true hyphae** (germ tubes) - Does not produce a polysaccharide capsule - Identified by germ tube formation at 37°C in serum

Q: A patient, a resident of Himachal Pradesh, presented with a series of ulcers in a row on his right leg. The biopsy from the affected area was taken and cultured on Sabouraud's dextrose agar. What is the most likely causative organism?

Sporothrix schenckii. ***Sporothrix schenckii*** - The presentation of "ulcers in a row" on the leg is highly suggestive of **lymphocutaneous sporotrichosis**, a characteristic finding where the infection spreads via lymphatic drainage. - This fungus is endemic in certain regions including parts of **Himachal Pradesh**, and is typically acquired through contact with contaminated soil or plant material (e.g., rose thorns, sphagnum moss). - Grows well on **Sabouraud's dextrose agar**, producing characteristic colonies. *Cladosporium spp.* - While *Cladosporium* can cause **phaeohyphomycosis** or allergic fungal sinusitis, it does not typically present with the classic lymphocutaneous lesions described. - These fungi are common environmental contaminants and their infections are usually associated with chronic skin lesions, not a linear spread of ulcers. *Pseudoallescheria boydii* - *Pseudoallescheria boydii* is a common cause of **mycetoma** (Madura foot), characterized by chronic, destructive lesions with granulomas and sinus tracts that discharge grains. - This presentation is distinct from the linear ulcerative lesions described in the patient. *Nocardia brasiliensis* - *Nocardia brasiliensis* is a bacterium (an actinomycete) that causes **actinomycetoma**, characterized by chronic, suppurative lesions with sinus tracts discharging grains. - The characteristic **"ulcers in a row"** (lymphocutaneous spread pattern) is **not typical** of Nocardia infection, which presents as localized mycetoma rather than ascending lymphatic involvement. - While Nocardia can grow on some fungal media, the clinical presentation is the key distinguishing feature here.

Q: Pityriasis versicolor is caused by which organism?

M. furfur. ***M. furfur*** - **Pityriasis versicolor** is caused by **Malassezia furfur** (also known as Pityrosporum ovale), a dimorphic yeast that is a normal inhabitant of human skin. - Under certain conditions (e.g., humidity, excessive sweating), it overgrows, leading to characteristic hypopigmented or hyperpigmented patches. *E. floccosum* - **Epidermophyton floccosum** is a dermatophyte known to cause **tinea pedis (athlete's foot)**, tinea cruris (jock itch), and tinea unguium (nail infections). - It does not cause pityriasis versicolor, which is a superficial yeast infection, not a dermatophyte infection. *M. gypseum* - **Microsporum gypseum** is a geophilic dermatophyte, meaning it is found in soil and can cause **tinea corporis** or **tinea capitis** in humans, often through contact with contaminated soil. - It is not associated with pityriasis versicolor. *T. tonsurans* - **Trichophyton tonsurans** is an anthropophilic dermatophyte, a common cause of **tinea capitis** (ringworm of the scalp) and sometimes tinea corporis, particularly in children. - It causes specific types of dermatophytosis and is not the causative agent of pityriasis versicolor.

Q: What is the definitive method for diagnosing Pneumocystis jirovecii pneumonia?

Finding cysts in tissue specimens. ***Finding cysts in tissue specimens*** - The definitive diagnosis of **Pneumocystis jirovecii pneumonia (PCP)** involves the microscopic identification of the **trophozoites** or **cysts** of the organism in respiratory secretions or tissue biopsies [1]. - This is typically achieved through techniques like **bronchoalveolar lavage (BAL)**, induced sputum, or transbronchial biopsy, followed by staining with methods such as **Gomori methenamine silver (GMS)** [1] or Giemsa. *Serological test* - Serological tests for PCP are **not definitive** for diagnosis, as antibodies to *P. jirovecii* can be found in a high percentage of healthy individuals due to widespread exposure. - These tests cannot distinguish between active infection, past exposure, or colonization, making them **unreliable** for acute diagnosis. *Chest X-ray* - A chest X-ray can show abnormalities like **diffuse bilateral interstitial infiltrates** or ground-glass opacities, which are highly suggestive of PCP in immunocompromised patients [1]. - However, these findings are **non-specific** and can be present in other pulmonary conditions, thus not providing a definitive diagnosis of PCP. *CT scan of thorax* - A CT scan of the thorax, particularly a **high-resolution CT (HRCT)**, is more sensitive than a chest X-ray and can reveal characteristic patterns such as **ground-glass opacities**, interstitial infiltrates, and sometimes cysts. - While highly suggestive, these imaging findings are **not specific enough** to definitively diagnose PCP and must be correlated with microbiological evidence. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 317-319.

Q: Which of the following classifications correctly describes fungi?

Eukaryotic organisms. ***Eukaryotic organisms*** - Fungi possess a **true nucleus** enclosed within a nuclear membrane and **membrane-bound organelles** like mitochondria and endoplasmic reticulum. - Their cells have a complex internal structure, distinguishing them from prokaryotes. *Prokaryotic organisms* - **Prokaryotes** lack a true nucleus and membrane-bound organelles; their genetic material is free in the cytoplasm. - Examples of prokaryotes include **bacteria** and archaea, not fungi. *Multicellular organisms* - While many fungi are **multicellular** (e.g., mushrooms), some are **unicellular** (e.g., yeasts), so this classification is not universally descriptive. - Thus, classifying all fungi solely as multicellular would be inaccurate. *Unicellular organisms* - While some fungi, such as **yeasts**, are unicellular, many others, like **molds** and mushrooms, are multicellular. - Therefore, classifying all fungi as unicellular is an **incomplete** description.

Q: Which is the MOST COMMON cause of atypical pneumonia in the community setting?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - *Mycoplasma pneumoniae* is the **most common cause of community-acquired atypical pneumonia**, particularly in children and young adults. - It causes "walking pneumonia" with **gradual onset**, low-grade fever, and **prominent dry cough** that is disproportionate to physical findings. - Lacks a **cell wall**, making it resistant to beta-lactam antibiotics; treatment is with macrolides or tetracyclines. - Characterized by **cold agglutinins** and extrapulmonary manifestations (hemolytic anemia, neurologic complications). *Chlamydophila pneumoniae* - A significant cause of atypical pneumonia, but **less common** than *M. pneumoniae* overall. - More common in **older adults** and causes a similar clinical picture with prolonged cough. - Also lacks a cell wall and responds to macrolides or tetracyclines. *Legionella pneumophila* - Causes **Legionnaires' disease**, a severe form of atypical pneumonia. - Less common overall, associated with **contaminated water sources** (cooling towers, hot tubs). - Presents with **high fever, gastrointestinal symptoms**, and hyponatremia; requires specific antibiotics like fluoroquinolones or macrolides. *Chlamydophila psittaci* - Causes **psittacosis** (ornithosis), a rare form of atypical pneumonia. - Acquired through exposure to **infected birds** (parrots, pigeons). - Much **less common** than *M. pneumoniae* in the general community setting.

Q: Which invasive fungal infection is most common in neutropenic patients?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - This species is a frequent cause of invasive aspergillosis, particularly in profoundly **neutropenic** patients or those with **immunocompromise**. - Its spores are ubiquitous in the environment and can cause severe lung infections when inhaled by vulnerable individuals. *Candida* - While *Candida* species are common causes of fungal infections in immunocompromised patients, including those with neutropenia, they typically cause **candidemia** or **mucocutaneous infections**. - **Invasive aspergillosis** is generally considered a more significant opportunistic mold infection in prolonged neutropenia than invasive candidiasis. *Histoplasma* - *Histoplasma capsulatum* is predominantly found in certain **geographic regions** (e.g., Ohio and Mississippi River valleys) and causes **pulmonary or disseminated histoplasmosis**, often after exposure to bird or bat droppings. - It is not as commonly associated with **acute severe neutropenia** as *Aspergillus fumigatus*. *Aspergillus niger* - While *Aspergillus niger* can cause infections, especially **otomycosis** or **aspergilloma**, it is far less commonly implicated in severe **invasive disease** in neutropenic patients compared to *Aspergillus fumigatus*. - *Aspergillus fumigatus* is the most pathogenic and prevalent *Aspergillus* species causing **invasive aspergillosis**.

Q: In an HIV-infected individual, the Gram stain of lung aspirate shows yeast-like morphology. Which of the following is the least likely diagnosis?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - While *Aspergillus* can cause pulmonary infections in immunosuppressed individuals, it typically presents as **hyphae**, not yeast-like morphology, on Gram stain. - Identification usually requires visualization of **septate hyphae with acute-angle branching**. *Candida tropicalis* - *Candida* species are common causes of opportunistic infections in HIV patients and present as **yeast and pseudohyphae** (though true hyphae can also be seen). - *Candida tropicalis* lung infection would appear as **yeast-like forms** on Gram stain, making it a plausible diagnosis. *Cryptococcus neoformans* - *Cryptococcus neoformans* is a significant pathogen in HIV-infected individuals, causing pulmonary and disseminated disease, and is characterized by its **yeast morphology** and prominent capsule. - Staining would reveal **budding yeast cells**, often with a clear halo due to the capsule, fitting the description. *Penicillium marneffei* - *Penicillium marneffei* is a dimorphic fungus endemic in Southeast Asia that causes disseminated infection in HIV patients, and it grows as **yeast-like cells** at body temperature. - In infected tissues, it appears as **intracellular and extracellular oval yeast-like cells** with transverse septation, consistent with the description.

Question 1

Which of the following is the MOST COMMON fungal cause of Mucormycosis?

Accepted Answer

Rhizopus oryzae

Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Question 2

Microscopy of a corneal ulcer shows branching septate hyphae. The probable diagnosis is

Accepted Answer

Aspergillus

Answer

Histoplasma

Answer

Candida

Answer

Mucormycosis

Question 3

Which organism is characterized by a wide polysaccharide capsule that appears as a clear halo around the yeast cell on India ink staining?

Accepted Answer

Cryptococcus neoformans

Answer

Penicillium marneffei

Answer

Blastomyces dermatitidis

Answer

Candida albicans

Question 4

A patient, a resident of Himachal Pradesh, presented with a series of ulcers in a row on his right leg. The biopsy from the affected area was taken and cultured on Sabouraud's dextrose agar. What is the most likely causative organism?

Accepted Answer

Sporothrix schenckii

Answer

Cladosporium spp.

Answer

Pseudoallescheria boydii

Answer

Nocardia brasiliensis

Question 5

Pityriasis versicolor is caused by which organism?

Accepted Answer

M. furfur

Answer

E. floccosum

Answer

M. gypseum

Answer

T. tonsurans

Question 6

What is the definitive method for diagnosing Pneumocystis jirovecii pneumonia?

Accepted Answer

Finding cysts in tissue specimens

Answer

Serological test

Answer

Chest X-ray

Answer

CT scan of thorax

Question 7

Which of the following classifications correctly describes fungi?

Accepted Answer

Eukaryotic organisms

Answer

Prokaryotic organisms

Answer

Multicellular organisms

Answer

Unicellular organisms

Question 8

Which is the MOST COMMON cause of atypical pneumonia in the community setting?

Accepted Answer

Mycoplasma pneumoniae

Answer

Legionella pneumophila

Answer

Chlamydophila psittaci

Answer

Chlamydophila pneumoniae

Question 9

Which invasive fungal infection is most common in neutropenic patients?

Accepted Answer

Aspergillus fumigatus

Answer

Histoplasma

Answer

Aspergillus niger

Answer

Candida

Question 10

In an HIV-infected individual, the Gram stain of lung aspirate shows yeast-like morphology. Which of the following is the least likely diagnosis?

Accepted Answer

Aspergillus fumigatus

Answer

Candida tropicalis

Answer

Cryptococcus neoformans

Answer

Penicillium marneffei

Mycology — MCQs

Mycology — MCQs

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