Mycology Practice Questions

Q: Meningitis in immunocompromised host is frequently caused by

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This encapsulated yeast is **the most common cause of fungal meningitis** in **immunocompromised individuals**, particularly those with **HIV/AIDS** (CD4 count <100 cells/μL). - Infection occurs through **inhalation of spores** from pigeon droppings and soil, causing primary **pulmonary infection** before disseminating to the **CNS**. - Diagnosis: **India ink staining** shows encapsulated yeasts; **CSF cryptococcal antigen** is highly sensitive. - Classic clinical features include **subacute headache, fever, and altered mental status**. *Trichophyton rubrum* - This is a common **dermatophyte** causing **superficial fungal infections** of skin, hair, and nails (e.g., **tinea pedis**, **onychomycosis**). - It remains **confined to keratinized tissues** and does not cause invasive or systemic infections like meningitis, even in immunocompromised patients. *Epidermophyton flocculosum* - Another **dermatophyte** causing superficial infections, particularly **tinea cruris** (jock itch) and **tinea pedis**. - Like *Trichophyton rubrum*, it **cannot invade beyond the epidermis** and is not associated with deep-seated infections or meningitis. *Candida tropicalis* - While *Candida* species can cause invasive infections in immunocompromised patients, **meningitis due to *Candida tropicalis*** is **relatively rare** compared to *Cryptococcus neoformans*. - *Candida* meningitis typically occurs in **neonates, post-neurosurgical patients**, or following **candidemia**, rather than as a primary CNS infection in AIDS patients.

Q: Which of the following is a false statement about the respective fungal infections?

Microsporium involves nail. ***Microsporium involves nail*** - This statement is considered **false** for exam purposes because *Microsporum* species are **NOT primary causes** of **tinea unguium** (onychomycosis). - *Microsporum* species primarily cause **tinea capitis** (scalp ringworm) and **tinea corporis** (body ringworm). While rare cases of nail involvement have been reported, it is clinically insignificant. - **Tinea unguium** (onychomycosis) is predominantly caused by ***Trichophyton rubrum*** and ***Trichophyton mentagrophytes***, with *Epidermophyton floccosum* and *Candida* species also playing roles. *Superficial layers of skin are involved* - This is a **true statement** because dermatophyte infections generally affect the **stratum corneum**, hair, and nails, which are all superficial keratinized tissues. - These fungi are unable to penetrate deeper viable tissue due to their inability to grow at core body temperature and the presence of inhibitory factors in serum. *Candida albicans causes skin infection* - This is a **true statement** as *Candida albicans* is a common cause of **cutaneous candidiasis**, manifesting as intertrigo, diaper rash, and paronychia. - It thrives in warm, moist environments and can infect skin folds, mucous membranes, and damaged skin. *Epidermophyton doesn't involve hair* - This is a **true statement** because *Epidermophyton floccosum* is unique among dermatophytes in that it primarily causes infections of the **skin** (tinea corporis, tinea cruris, tinea pedis) and **nails** (onychomycosis) but **does not infect hair follicles**. - Unlike *Trichophyton* and *Microsporum*, *Epidermophyton* lacks the enzymatic machinery to invade hair shafts.

Q: 'Pityriasis versicolor' is caused by:

Malassezia furfur. ***Malassezia furfur*** - **Pityriasis versicolor** is a superficial fungal infection of the skin caused by the dimorphic yeast **Malassezia furfur** (also known as Pityrosporum ovale). - This organism is part of the normal skin flora but can become pathogenic under certain conditions, leading to characteristic **hypopigmented or hyperpigmented patches**, often on the trunk. *Nocardia species* - **Nocardia** are aerobic, gram-positive bacteria that typically cause **pulmonary, cutaneous, or disseminated infections**, particularly in immunocompromised individuals. - They are known for causing conditions like **nocardiosis**, which presents with abscesses, not pityriasis versicolor. *Aspergillus fumigatus* - **Aspergillus fumigatus** is a common mold that can cause a range of diseases, primarily in the respiratory tract, including **allergic bronchopulmonary aspergillosis (ABPA)**, **aspergilloma**, and **invasive aspergillosis**. - It is not associated with superficial skin infections like pityriasis versicolor. *Trichophyton rubrum* - **Trichophyton rubrum** is a dermatophyte fungus that commonly causes **tinea (ringworm) infections** of the skin, hair, and nails, such as **athlete's foot (tinea pedis)**, **jock itch (tinea cruris)**, and **nail infections (onychomycosis)**. - Unlike Malassezia, it invades the keratinized structures of the epidermis, not just superficial layers causing versicolor lesions.

Q: A patient from the Ohio River valley presents with granulomatous prostatitis showing broad-based budding organisms on microscopy. What is the most likely infecting organism?

Blastomyces dermatitidis. ***Blastomyces dermatitidis*** - This organism is endemic to the **Ohio River valley** and is known to cause **granulomatous inflammation**, including in the prostate. - Its characteristic morphology is **broad-based budding yeast** on microscopy, fitting the description. *Escherichia coli* - While *E. coli* is a common cause of **bacterial prostatitis**, it does not present as granulomatous inflammation. - It is a **bacterium**, not a fungus, and would not show broad-based budding organisms. *Histoplasma capsulatum* - **Histoplasma** is also endemic to the Ohio River valley and causes granulomatous disease, but its yeast forms are **small**, intracellular, and do not exhibit broad-based budding. - It is often associated with a history of exposure to **bat or bird droppings** and commonly affects the lungs. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* causes **bacterial infections**, often in immunocompromised individuals or associated with catheter use, and is not a fungus. - It causes **acute inflammation**, not chronic granulomatous inflammation, and does not show broad-based budding.

Q: The yeast which shows thick gelatinous capsule and positive for mucicarmine is

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This yeast is uniquely characterized by its prominent **polysaccharide capsule**, which appears as a thick, gelatinous layer around the cell. - The capsule stains **red with mucicarmine**, a special stain used to highlight mucopolysaccharides, aiding in its identification. *Paracoccidioides brasiliensis* - This dimorphic fungus is known for its **"pilot wheel"** or **"mariner's wheel"** appearance in tissue, with multiple budding cells. - It does not possess a thick, gelatinous capsule nor does it stain positively with mucicarmine in the same distinct manner as *Cryptococcus*. *Histoplasma capsulatum* - This dimorphic fungus is typically visualized as **small, oval yeast cells** found within macrophages in tissue. - It lacks a prominent capsule and does not stain with mucicarmine. *Blastomyces dermatitidis* - This dimorphic fungus is characterized by its **large, broad-based budding yeast cells** in tissue. - It does not have a capsule and is not identified by mucicarmine staining.

Q: Which one of the following diseases is endogenous in origin-

Candidiasis. ***Candidiasis*** - **Candidiasis** is an **endogenous** infection because it is caused by species of *Candida*, especially *Candida albicans*, which is part of the normal human microbiota (e.g., in the oral cavity, gastrointestinal tract, and vagina). - Infection occurs when there is an imbalance in the host's immune system or a disruption in the normal flora, allowing *Candida* to overgrow and cause disease. *Aspergillosis* - **Aspergillosis** is typically an **exogenous** infection caused by inhaling **spores of *Aspergillus*** species, which are ubiquitous in the environment (e.g., soil, decaying vegetation, air). - It is not caused by organisms that are part of the normal human microbiota. *All of the above* - This option is incorrect because aspergillosis and phycomycosis are primarily exogenous infections, not endogenous. *Phycomycosis* - **Phycomycosis** (now more commonly referred to as mucormycosis or zygomycosis) is an **exogenous** infection resulting from inhalation or inoculation of **spores of fungi** belonging to the Mucorales order, which are found in the environment (e.g., soil, decaying matter). - These fungi are not part of the normal human microbiota.

Q: Which is a eukaryote among the following?

Fungus. ***Fungus*** - Fungi are characterized by having a **true nucleus** and **membrane-bound organelles**, essential features of eukaryotic cells. - This cellular organization allows for complex metabolic processes and differentiation, distinguishing them from prokaryotes. *Mycoplasma* - Mycoplasma are among the **smallest bacteria** and are **prokaryotic**, lacking a nucleus and other membrane-bound organelles. - They are unique among bacteria for lacking a **cell wall**. *Bacteria* - Bacteria are **prokaryotic organisms**, meaning they do not possess a **membrane-bound nucleus** or other membrane-bound organelles. - Their genetic material is located in a **nucleoid region** within the cytoplasm. *Chlamydia* - Chlamydia are **obligate intracellular prokaryotes** that are classified as bacteria. - They lack a true nucleus and membrane-bound organelles, characteristic of all prokaryotic cells.

Q: Which of the following is most likely to be acquired by traumatic inoculation?

Sporothrix schenckii. ***Sporothrix schenckii*** - **Sporothrix schenckii** causes **sporotrichosis** (rose gardener's disease), which is classically acquired through **traumatic inoculation** via thorns, splinters, or plant material contaminated with the fungus. - This dimorphic fungus exists in soil and vegetation, and the mode of transmission is characteristically associated with **gardeners, farmers, and florists** who experience penetrating injuries during their work. - Presents as lymphocutaneous infection with nodular lesions along lymphatic channels. *Histoplasma capsulatum* - Causes histoplasmosis and is endemic to certain regions (Ohio and Mississippi River valleys). - Primarily acquired through **inhalation of microconidia** from soil contaminated with bird or bat droppings, not through traumatic inoculation. - Presents as pulmonary infection in most cases. *Coccidioides immitis* - Causes coccidioidomycosis (Valley Fever) and is found in arid regions of southwestern United States. - Acquired through **inhalation of airborne arthroconidia** from disturbed soil, not through traumatic inoculation. - While rare cases of primary cutaneous infection can occur, inhalation remains the typical route. *Aspergillus fumigatus* - Ubiquitous environmental mold associated with decaying organic matter. - Primarily causes disease through **inhalation of conidia**, leading to allergic reactions, aspergilloma, or invasive aspergillosis in immunocompromised patients. - Not typically associated with traumatic inoculation as the primary mode of infection.

Q: Which is not a dimorphic fungus?

Pneumocystis jirovecii. **Pneumocystis jirovecii** * **Pneumocystis jirovecii** is an **atypical fungus** that does not exhibit dimorphism; it solely exists in a **trophic form** and a **cystic form**, both of which are obligate parasites in the host. * It is classified on genetic findings as a fungus but lacks characteristic fungal cell wall components like ergosterol, making it unique and not a dimorphic fungus. * *P. marneffi* (now *Talaromyces marneffei*) * *P. marneffei* is a **thermally dimorphic fungus** that grows as molds at 25°C with characteristic **red pigment production** and as yeast cells at 37°C. * It causes penicilliosis, an **opportunistic infection** particularly in immunocompromised individuals. * *Histoplasma capsulatum* * *Histoplasma capsulatum* is a **thermally dimorphic fungus** that grows as a mold with tuberculate macroconidia in soil and converts to small, oval budding yeasts at 37°C in host tissues. * It is known for causing **histoplasmosis**, often acquired through inhalation of spores from bird or bat droppings. * *Blastomyces dermatitidis* * *Blastomyces dermatitidis* is a **thermally dimorphic fungus** that grows as a filamentous mold in the environment and as large, **broad-based budding yeast** cells at body temperature in host tissues. * It causes **blastomycosis**, which can manifest as pulmonary, cutaneous, or disseminated disease.

Q: Beta-1,3-D-glucan assay is not useful for the diagnosis of

Mucormycosis. ***Mucormycosis*** - Fungi causing mucormycosis (e.g., *Rhizopus*, *Mucor*) have **minimal or no beta-glucans** in their cell walls, making the assay ineffective for diagnosis. - The cell wall of Mucorales is primarily composed of **chitosan** and **chitin**, not beta-glucans. *Aspergillosis* - **Beta-glucans** are a major component of the cell wall of *Aspergillus* species. - The assay can be useful in diagnosing **invasive aspergillosis**, especially when galactomannan testing is challenging. *Invasive candidiasis* - **Beta-glucans** are abundant in the cell walls of *Candida* species and are released during invasive infection. - The assay is a valuable tool for the **early diagnosis** and monitoring of invasive candidiasis. *Pneumocystis jirovecii* - **Beta-glucans** are a key structural component of the cell wall of *Pneumocystis jirovecii*. - The beta-glucan assay is highly sensitive for diagnosing **Pneumocystis pneumonia (PJP)**, particularly in immunocompromised patients.

Question 1

Meningitis in immunocompromised host is frequently caused by

Accepted Answer

Cryptococcus neoformans

Answer

Trichophyton rubrum

Answer

Epidermophyton flocculosum

Answer

Candida tropicalis

Question 2

Which of the following is a false statement about the respective fungal infections?

Accepted Answer

Microsporium involves nail

Answer

Superficial layers of skin are involved

Answer

Candida albicans causes skin infection

Answer

Epidermophyton doesn't involve hair

Question 3

'Pityriasis versicolor' is caused by:

Accepted Answer

Malassezia furfur

Answer

Nocardia species

Answer

Aspergillus fumigatus

Answer

Trichophyton rubrum

Question 4

A patient from the Ohio River valley presents with granulomatous prostatitis showing broad-based budding organisms on microscopy. What is the most likely infecting organism?

Accepted Answer

Blastomyces dermatitidis

Answer

Escherichia coli

Answer

Histoplasma capsulatum

Answer

Pseudomonas aeruginosa

Question 5

The yeast which shows thick gelatinous capsule and positive for mucicarmine is

Accepted Answer

Cryptococcus neoformans

Answer

Paracoccidioides brasiliensis

Answer

Histoplasma capsulatum

Answer

Blastomyces dermatitidis

Question 6

Which one of the following diseases is endogenous in origin-

Accepted Answer

Candidiasis

Answer

Aspergillosis

Answer

Phycomycosis

Answer

All of the above

Question 7

Which is a eukaryote among the following?

Accepted Answer

Fungus

Answer

Mycoplasma

Answer

Bacteria

Answer

Chlamydia

Question 8

Which of the following is most likely to be acquired by traumatic inoculation?

Accepted Answer

Sporothrix schenckii

Answer

Coccidioides immitis

Answer

Histoplasma capsulatum

Answer

Aspergillus fumigatus

Question 9

Which is not a dimorphic fungus?

Accepted Answer

Pneumocystis jirovecii

Answer

P. marneffi

Answer

Histoplasma capsulatum

Answer

Blastomyces dermatitidis

Question 10

Beta-1,3-D-glucan assay is not useful for the diagnosis of

Accepted Answer

Mucormycosis

Answer

Aspergillosis

Answer

Invasive candidiasis

Answer

Pneumocystis jirovecii

Mycology — MCQs

Mycology — MCQs

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