Mycology Practice Questions

Q: What type of microorganism is Cryptococcus neoformans?

Fungus. ***Fungus*** - *Cryptococcus neoformans* is an encapsulated **yeast** that is a common cause of fungal infections, particularly in immunocompromised individuals. - It is known to cause **cryptococcosis**, which can manifest as pneumonia or meningoencephalitis. *Bacteria* - Bacteria are **prokaryotic organisms** and do not possess a true nucleus or membrane-bound organelles, unlike *Cryptococcus neoformans*. - They are typically much smaller than fungi and have distinct cell wall compositions. *Virus* - Viruses are **acellular infectious agents** that require a host cell to replicate; they are not living organisms in the traditional sense. - They are significantly smaller than fungi and lack cellular structures such as a cell wall or organelles. *Parasite* - Parasites are **eukaryotic organisms** that live on or in a host and obtain nutrients at the host's expense, often involving complex life cycles. - While both are eukaryotes, fungi like *Cryptococcus neoformans* are distinct from parasitic protozoa or helminths in their biology and infectious mechanisms.

Q: In an immunocompromised patient with pulmonary symptoms, bronchoalveolar lavage reveals septate hyphae with acute angle branching. What is the likely pathogen?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - The presence of **septate hyphae with acute angle branching** on bronchoalveolar lavage is a classic microscopic finding for *Aspergillus* species, particularly *A. fumigatus*, in immunocompromised patients with pulmonary symptoms. - *Aspergillus* infections often present as **invasive pulmonary aspergillosis** in severely immunocompromised individuals, leading to pneumonia and other lung pathologies. *Mucor species* - *Mucor* species are characterized by **broad, ribbon-like, aseptate or sparsely septate hyphae with irregular, wide-angle branching** (typically 90 degrees), which differs from the acute angle branching seen in *Aspergillus*. - They are known to cause **mucormycosis**, often presenting as rhinocerebral, pulmonary, or cutaneous infections, particularly in patients with **diabetes** or profound immunosuppression. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as small, **oval yeasts** within macrophages in tissue samples, rather than septate hyphae outside of macrophages. - It causes **histoplasmosis**, an endemic fungal infection associated with exposure to **bird or bat droppings**, and can lead to pulmonary disease, especially in immunocompromised patients. *Candida albicans* - *Candida albicans* typically appears as **budding yeasts** and **pseudohyphae** (elongated yeast cells that resemble hyphae but are constricted at the septa) on microscopy. True septate hyphae with acute angle branching are not its characteristic morphology in tissue. - While *Candida* can cause pulmonary infections in severely immunocompromised patients, it more commonly causes **mucosal infections** (e.g., thrush, esophagitis) or **candidemia**.

Q: Which combination of staining methods is best for visualizing the capsule of Cryptococcus neoformans in cerebrospinal fluid (CSF)?

India ink preparation and Mucicarmine stain. ***India ink preparation and Mucicarmine stain*** - **India ink preparation** is ideal for visualizing the **capsule** of *Cryptococcus neoformans* as it stains the background dark, making the clear halo of the capsule visible around the yeast cells. - **Mucicarmine stain** specifically highlights the **polysaccharide capsule** of *Cryptococcus* in red or pink, confirming its presence and aiding in differentiation. *Gram stain and Giemsa stain* - **Gram stain** is used to classify bacteria based on their cell wall, but it stains *Cryptococcus* as **Gram-positive** and does not effectively visualize the capsule. - **Giemsa stain** is used for blood parasites and intracellular structures but is not specific or effective for demonstrating the *Cryptococcus* capsule. *Leishman stain and Gram stain* - **Leishman stain** is primarily used for blood and bone marrow smears to visualize cells and parasites, offering no specific advantage for *Cryptococcus* capsule visualization. - **Gram stain**, as mentioned, stains fungal cells but does not provide clear capsular visualization. *Giemsa stain and Ponder's stain* - **Giemsa stain** is not optimal for visualizing the *Cryptococcus* capsule. - **Ponder's stain** (or Albert's stain) is primarily used for demonstrating metachromatic granules in *Corynebacterium diphtheriae* and is not useful for fungal capsules.

Q: A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?

Rhizopus spp.. ***Rhizopus spp.*** - The patient's presentation with **sinus pain**, **nasal discharge**, **facial swelling**, and a history of **poorly controlled diabetes** is classic for **mucormycosis** (also known as zygomycosis). - **Biopsy findings** of **broad, nonseptate hyphae branching at wide/irregular angles** are pathognomonic for mucormycosis, most commonly caused by *Rhizopus* species. - Diabetes mellitus, particularly when poorly controlled with **ketoacidosis**, is a major risk factor for rhinocerebral mucormycosis. *Aspergillus fumigatus* - This fungus typically causes infections with **septate hyphae** that **branch at acute angles** (45 degrees), which is morphologically distinct from mucormycosis. - While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, the specific hyphal morphology (nonseptate, wide-angle branching) points away from it. *Candida albicans* - *Candida albicans* is a yeast that typically appears as **oval budding cells** and **pseudohyphae** on microscopy, not broad, nonseptate hyphae. - While it can cause opportunistic infections in diabetic and immunocompromised patients, its microscopic appearance is entirely inconsistent with the biopsy findings. *Cryptococcus neoformans* - *Cryptococcus neoformans* is an **encapsulated yeast** that is typically identified by its **spherical or oval budding cells** with a characteristic **polysaccharide capsule** visible with India ink stain. - It primarily causes **meningitis** and pulmonary infections in immunocompromised hosts, and its morphology (yeast, not hyphae) is entirely different from the described findings.

Q: A 50-year-old farmer with diabetes presents with a chronic ulcer on his foot that has not healed despite standard wound care. A biopsy reveals fungal elements, and the culture grows a mold with septate hyphae and green conidia. What is the likely causative organism?

Aspergillus fumigatus. **Aspergillus fumigatus** - The presence of **septate hyphae** and **green conidia** on culture is characteristic of *Aspergillus* species, particularly *Aspergillus fumigatus*. - Patients with **diabetes** are at a higher risk for fungal infections, and chronic non-healing ulcers can be a presentation of localized **aspergillosis**. *Candida albicans* - *Candida albicans* typically presents as **yeast** and **pseudohyphae** on microscopy, not septate hyphae with green conidia. - While it can cause chronic ulcers, its microscopic morphology and culture characteristics differ significantly from the description. *Rhizopus oryzae* - *Rhizopus oryzae* is a **mucormycete** characterized by **broad, aseptate hyphae** with right-angle branching, which contrasts with the septate hyphae described. - It causes mucormycosis, a severe infection often involving the rhinocerebral area, though cutaneous forms can occur. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as small, oval budding yeasts within macrophages in tissue. - It is typically associated with pulmonary infections and disseminated disease, not chronic foot ulcers with septate hyphae and green conidia on culture.

Q: A patient with AIDS presents with meningitis. An India ink preparation of the cerebrospinal fluid shows encapsulated yeast cells. Which organism is most likely responsible?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This organism is a **common cause of meningitis in AIDS patients** due to their severely compromised immune systems (low CD4 counts). - The presence of **encapsulated yeast cells** visible on an **India ink preparation of CSF** is pathognomonic for *Cryptococcus neoformans*. - The **India ink negative staining technique** highlights the thick polysaccharide capsule, which appears as a clear halo around the yeast cells against a dark background. *Candida albicans* - While *Candida albicans* can cause various infections in immunocompromised individuals, **Candidal meningitis is rare** and would not typically show encapsulated yeast on India ink. - *Candida* usually presents as **pseudohyphae and budding yeasts** and is not primarily identified by India ink preparations for capsules in CSF. *Histoplasma capsulatum* - *Histoplasma capsulatum* can cause **disseminated histoplasmosis**, including central nervous system involvement, especially in AIDS patients. - However, it is an **intracellular dimorphic fungus** and does not typically present as encapsulated yeast in the CSF on India ink stain. *Coccidioides immitis* - *Coccidioides immitis* can cause **Coccidioidal meningitis**, particularly in endemic areas and immunocompromised patients. - It is characterized by **spherules containing endospores** in tissue and CSF, not encapsulated yeast cells.

Q: Sabouraud's dextrose agar is primarily used for the isolation of which of the following?

Candida albicans. ***Candida albicans*** - **Sabouraud's dextrose agar (SDA)** is the gold standard medium for **isolation of all fungi** (both yeasts and molds), formulated with low pH (5.6) and high glucose concentration to favor fungal growth while inhibiting most bacteria. - Among the fungal options listed, ***Candida albicans*** is the **best answer** because Candida species are the **most commonly encountered fungal pathogens** in clinical microbiology, making SDA most frequently used for their isolation in routine clinical practice. - While SDA supports growth of all fungi including Aspergillus and Rhizopus, **Candida species** (especially *C. albicans*) represent the majority of clinical fungal infections requiring laboratory diagnosis. *Staphylococcus aureus* - This is a **bacterium**, not a fungus. - The **low pH (5.6)** and high sugar content of SDA are specifically designed to **inhibit bacterial growth** while promoting fungal growth. - *Staphylococcus aureus* is isolated on bacterial media like **blood agar** or **mannitol salt agar (MSA)**, not fungal media. *Aspergillus niger* - This is a **filamentous fungus (mold)** that grows very well on SDA. - However, while *Aspergillus* species are important opportunistic pathogens, they are **less commonly isolated** in routine clinical microbiology compared to *Candida* species. - *Aspergillus* infections occur primarily in immunocompromised patients, whereas *Candida* infections are more frequent across all patient populations. *Rhizopus stolonifer* - This is a **zygomycete fungus (bread mold)** that can grow on SDA. - While *Rhizopus* species cause mucormycosis in susceptible hosts, these infections are **relatively uncommon** compared to candidiasis. - SDA supports *Rhizopus* growth, but this organism is not the primary target in routine clinical fungal isolation.

Q: Which organism is associated with a positive hair perforation test?

Trichophyton. ***Correct Option: Trichophyton*** - The **hair perforation test** is used to identify dermatophytes that can produce **wedge-shaped perforations** in sterilized hair shafts *in vitro* - **Trichophyton mentagrophytes** and related species (like *T. mentagrophytes var. mentagrophytes*) are classically **positive** for this test - This test helps distinguish between: - **Positive species:** *T. mentagrophytes* (causes perforations) - **Negative species:** *T. rubrum* (does not perforate hair) - The test involves incubating dermatophytes with sterilized blonde human hair in sterile water for 2-4 weeks and examining for characteristic perforations under microscopy - Among dermatophyte genera, **Trichophyton** is the primary genus associated with positive hair perforation tests in clinical microbiology *Incorrect Option: Microsporum* - *Microsporum* species cause **ectothrix** hair invasion patterns in vivo but generally do **not produce positive hair perforations** in the standardized *in vitro* test - *Microsporum canis* and other species in this genus typically yield negative results *Incorrect Option: Epidermophyton* - *Epidermophyton floccosum* is the only medically significant species in this genus - It causes **skin and nail infections** (tinea corporis, cruris, pedis) but does **not infect hair** - Therefore, it cannot produce positive hair perforation test results *Incorrect Option: None of the options* - This is incorrect because **Trichophyton** (specifically *T. mentagrophytes*) is the standard correct answer for organisms showing positive hair perforation tests in medical microbiology

Q: Chlamydospore is formed by ?

Candida albicans. ***Candida albicans*** - *Candida albicans* is distinguished by its ability to form **chlamydospores** when cultured under specific conditions, which is an important diagnostic feature. - These are thick-walled, spherical spores, often found terminally or intercalary, that aid in its identification in the laboratory. *Candida tropicalis* - While *Candida tropicalis* is another clinically significant *Candida* species, it typically does not produce **chlamydospores**. - Its identification relies on other biochemical tests and macroscopic/microscopic morphological characteristics like **pseudohyphae** and **blastoconidia**. *Histoplasma* - *Histoplasma capsulatum* is a **dimorphic fungus** known for causing **histoplasmosis**, and its morphology includes **tuberculate macroconidia** and microconidia, not chlamydospores. - It exists as a mold in the environment and a yeast in human tissues. *Cryptococcus* - *Cryptococcus neoformans* is an **encapsulated yeast** primarily identified by its prominent **polysaccharide capsule** and urease production. - It is known for causing **cryptococcosis**, especially in immunocompromised individuals, and does not form chlamydospores.

Q: Which fungus is primarily responsible for causing Ectothrix infections?

Microsporum canis. ***Microsporum canis*** - This fungus is a common cause of **tinea capitis** (scalp ringworm) and typically produces an **ectothrix** pattern of hair invasion. - In ectothrix infections, **arthroconidia** are formed on the **outside** of the hair shaft, damaging the hair cuticle. - *M. canis* is the **most common** cause of ectothrix infections, often transmitted from cats and dogs. *Trichophyton tonsurans* - This species is known for causing **endothrix** hair infections, where arthroconidia are formed **inside** the hair shaft, *without* affecting the cuticle. - It often leads to **black dot tinea capitis**, characterized by broken hair shafts at the scalp surface. *Trichophyton violaceum* - Similar to *Trichophyton tonsurans*, *Trichophyton violaceum* primarily causes **endothrix** hair infections. - It is associated with highly inflammatory scalp lesions and can also result in black dot tinea capitis. *Trichophyton mentagrophytes* - While this fungus **can** cause ectothrix infections, it is much **less common** than *Microsporum canis*. - *T. mentagrophytes* more frequently causes tinea corporis, tinea pedis, and tinea cruris rather than tinea capitis. - When it does affect hair, it may produce both ectothrix and endothrix patterns depending on the variant.

Question 1

What type of microorganism is Cryptococcus neoformans?

Accepted Answer

Fungus

Answer

Bacteria

Answer

Virus

Answer

Parasite

Question 2

In an immunocompromised patient with pulmonary symptoms, bronchoalveolar lavage reveals septate hyphae with acute angle branching. What is the likely pathogen?

Accepted Answer

Aspergillus fumigatus

Answer

Mucor species

Answer

Histoplasma capsulatum

Answer

Candida albicans

Question 3

Which combination of staining methods is best for visualizing the capsule of Cryptococcus neoformans in cerebrospinal fluid (CSF)?

Accepted Answer

India ink preparation and Mucicarmine stain

Answer

Gram stain and Giemsa stain

Answer

Leishman stain and Gram stain

Answer

Giemsa stain and Ponder's stain

Question 4

A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?

Accepted Answer

Rhizopus spp.

Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Cryptococcus neoformans

Question 5

A 50-year-old farmer with diabetes presents with a chronic ulcer on his foot that has not healed despite standard wound care. A biopsy reveals fungal elements, and the culture grows a mold with septate hyphae and green conidia. What is the likely causative organism?

Accepted Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Rhizopus oryzae

Answer

Histoplasma capsulatum

Question 6

A patient with AIDS presents with meningitis. An India ink preparation of the cerebrospinal fluid shows encapsulated yeast cells. Which organism is most likely responsible?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Histoplasma capsulatum

Answer

Coccidioides immitis

Question 7

Sabouraud's dextrose agar is primarily used for the isolation of which of the following?

Accepted Answer

Candida albicans

Answer

Staphylococcus aureus

Answer

Aspergillus niger

Answer

Rhizopus stolonifer

Question 8

Which organism is associated with a positive hair perforation test?

Accepted Answer

Trichophyton

Answer

None of the options

Answer

Microsporum

Answer

Epidermophyton

Question 9

Chlamydospore is formed by ?

Accepted Answer

Candida albicans

Answer

Candida tropicalis

Answer

Histoplasma

Answer

Cryptococcus

Question 10

Which fungus is primarily responsible for causing Ectothrix infections?

Accepted Answer

Microsporum canis

Answer

Trichophyton tonsurans

Answer

Trichophyton violaceum

Answer

Trichophyton mentagrophytes

Mycology — MCQs

Mycology — MCQs

On this page

Practice by Chapter

Want unlimited practice?