Mycology Practice Questions

Q: Chest x-ray is showing reticulonodular pattern. The causative agent is?

Pneumocystis jirovecii. ***Pneumocystis jirovecii*** - **Pneumocystis pneumonia (PCP)**, caused by *Pneumocystis jirovecii*, classically presents with a **diffuse reticulonodular or ground-glass infiltrate** on chest X-ray. - This organism primarily affects **immunocompromised individuals**, such as those with HIV/AIDS, making this radiographic pattern highly suggestive. *Staph aureus* - *Staphylococcus aureus* pneumonia typically presents with **lobar consolidation**, **cavities**, or **abscess formation**, not a widespread reticulonodular pattern. - It's a common cause of **healthcare-associated pneumonia** and **secondary bacterial pneumonia** after viral infections. *Pneumococcus* - *Streptococcus pneumoniae* (Pneumococcus) usually causes **lobar pneumonia**, characterized by **homogenous consolidation** in one or more lung lobes. - While it's the most common cause of community-acquired pneumonia, it does not typically produce a reticulonodular pattern. *Pseudomonas* - *Pseudomonas aeruginosa* pneumonia often presents with **bronchopneumonia** or **necrotizing pneumonia**, frequently seen in **ventilated patients** or those with **cystic fibrosis**. - Radiographic findings can include **multi-lobar infiltrates**, **cavitation**, and **effusions**, which differ from a reticulonodular pattern.

Q: Non-parasitic eosinophilia is caused by infection with -

Coccidioidomycosis (Valley Fever). ***Coccidioidomycosis (Valley Fever)*** - **Coccidioidomycosis** is a systemic fungal infection that characteristically causes **non-parasitic eosinophilia**. This is a classic association frequently tested. - The host immune response to this specific fungal pathogen often involves a significant increase in **eosinophil count**. *Ehrlichiosis* - **Ehrlichiosis** is a bacterial infection transmitted by ticks, which typically causes **leukopenia** (low white blood cell count), sometimes with relative lymphocytosis. - While it affects various blood cell lines, it does not characteristically lead to **eosinophilia**; rather, it's more associated with low platelet and white cell counts. *Candidiasis (Yeast infection)* - **Candidiasis** is a common fungal infection, but it almost never causes **eosinophilia** [1]. - Systemic candidiasis is more likely to cause **neutrophilia**, rather than an increase in eosinophils [1]. *Staphylococcal infection* - **Staphylococcal infections** are bacterial and typically cause **neutrophilia** as the primary response.

Q: Which of the following fungi is classified as lipophilic?

Malassezia furfur. ***Malassezia furfur*** - **Malassezia furfur** is a genus of fungi that is **lipophilic**, meaning it requires **lipids for growth** and must be cultured on **media supplemented with olive oil or long-chain fatty acids**. - It causes conditions like **pityriasis versicolor** and **seborrheic dermatitis**, thriving in oily skin areas. - This is the classic example of a lipid-dependent fungus in medical microbiology. *Candida* - **Candida** is a genus of yeast that is **not lipophilic**; it grows well on various sugar-containing media like Sabouraud dextrose agar. - It is a common cause of **mucocutaneous infections** like thrush and candidiasis, and opportunistic systemic infections. *Cryptococcus* - **Cryptococcus** is a yeast known for causing **meningitis** and pulmonary infections, especially in immunocompromised individuals. - It is **not lipophilic** and typically grows on media designed for general fungal growth. *Histoplasma* - **Histoplasma capsulatum** is a dimorphic fungus that causes **histoplasmosis**, primarily affecting the lungs. - It is **not lipophilic** and grows in soil enriched with bird or bat droppings.

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.

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: What is the primary component that dermatophytes infect?

Keratin. ***Correct: Keratin*** - **Dermatophytes** are a specific type of fungi that have the unique ability to metabolize and survive on **keratin**, a fibrous structural protein found in skin, hair, and nails. - This **keratinolytic ability** allows them to infect and thrive in the outermost layer of the skin and its appendages. - Dermatophytes produce **keratinase enzymes** that break down keratin, making it their defining characteristic and primary nutritional source. *Incorrect: Epidermis* - While dermatophytes infect the **epidermis**, it is specifically the **keratinized cells** within the epidermis (stratum corneum) that they target, not the entire epidermal layer. - The epidermis itself is a complex structure with various cell types, but the primary nutritional source for dermatophytes within it is keratin. *Incorrect: Hair* - **Hair** is an appendage rich in keratin and can indeed be infected by dermatophytes, leading to conditions like **tinea capitis** (ringworm of the scalp). - However, keratin is the fundamental component in hair that dermatophytes utilize, making "keratin" a more encompassing and primary answer. *Incorrect: Nails* - **Nails** are also composed primarily of keratin and are a common site for dermatophyte infections, resulting in **onychomycosis**. - Similar to hair, while nails are a site of infection, the specific substance within them that dermatophytes target and rely upon is keratin.

Q: Black piedra is caused by ?

Piedraia hortae. ***Piedraia hortae*** - **Black piedra** is a superficial fungal infection of the hair shaft, characterized by the formation of hard, dark brown to black nodules, and it is specifically caused by the ascomycetous fungus **_Piedraia hortae_**. - This fungus produces **ascospores** within the hair nodule, a key diagnostic feature. *Trichosporon asahii* - **_Trichosporon asahii_** is primarily associated with **white piedra** and systemic infections, particularly in immunocompromised individuals. - Unlike **black piedra**, white piedra manifests as soft, white to light brown nodules on the hair shaft. *Trichosporon ovoides* - **_Trichosporon ovoides_** is another species associated with **white piedra**, especially affecting scalp hair. - While it causes hair shaft infections, the characteristic nodules are soft and lighter in color, not the hard, dark nodules of black piedra. *Trichosporon inkin* - **_Trichosporon inkin_** is a species of **_Trichosporon_** known to cause **white piedra**, often affecting pubic hair. - It also causes systemic infections, but it is not the causative agent of **black piedra**.

Q: Which of the following statements about Cryptococcus is false?

Urease negative. ***Urease negative*** - *Cryptococcus neoformans* is **urease positive**, not urease negative, meaning it produces the enzyme urease, which breaks down urea into ammonia and carbon dioxide. - The urease test is a **key biochemical test** used for laboratory identification of *Cryptococcus*. - This statement is **false** and therefore the correct answer to the question. *Urease positive* - *Cryptococcus neoformans* is indeed **urease positive**, a characteristic often used in its laboratory identification. - This is a **true statement** about *Cryptococcus*. *Encapsulated yeast* - *Cryptococcus neoformans* possesses a **thick polysaccharide capsule** that is its major virulence factor. - The capsule can be demonstrated using **India ink stain**, which shows a clear halo around the yeast cell. - This is a **true statement** about *Cryptococcus*. *Primarily infects lung* - *Cryptococcus neoformans* infection typically begins with **inhalation of spores** (basidiospores), leading to primary pulmonary infection. - While it can disseminate to the central nervous system (causing meningitis), the **lung is the primary site of infection**. - This is a **true statement** about *Cryptococcus*.

Question 1

Chest x-ray is showing reticulonodular pattern. The causative agent is?

Accepted Answer

Pneumocystis jirovecii

Answer

Staph aureus

Answer

Pneumococcus

Answer

Pseudomonas

Question 2

Non-parasitic eosinophilia is caused by infection with -

Accepted Answer

Coccidioidomycosis (Valley Fever)

Answer

Ehrlichiosis

Answer

Candidiasis (Yeast infection)

Answer

Staphylococcal infection

Question 3

What is the primary method for diagnosing Pneumocystis jirovecii pneumonia?

Accepted Answer

Bronchoalveolar lavage (BAL)

Answer

Sputum microscopy

Answer

Chest X-ray findings

Answer

Serum beta-D-glucan assay

Question 4

Which of the following fungi is classified as lipophilic?

Accepted Answer

Malassezia furfur

Answer

Candida

Answer

Cryptococcus

Answer

Histoplasma

Question 5

Which fungus is primarily responsible for causing Ectothrix infections?

Accepted Answer

Microsporum canis

Answer

Trichophyton tonsurans

Answer

Trichophyton violaceum

Answer

Trichophyton mentagrophytes

Question 6

Chlamydospore is formed by ?

Accepted Answer

Candida albicans

Answer

Candida tropicalis

Answer

Histoplasma

Answer

Cryptococcus

Question 7

What is the primary component that dermatophytes infect?

Accepted Answer

Keratin

Answer

Epidermis

Answer

Hair

Answer

Nails

Question 8

Black piedra is caused by ?

Accepted Answer

Piedraia hortae

Answer

Trichosporon ovoides

Answer

Trichosporon inkin

Answer

Trichosporon asahii

Question 9

Which of the following statements about Pneumocystis jirovecii is correct?

Accepted Answer

Usually diagnosed by examining respiratory secretions.

Answer

Can be associated with CMV infection in some cases.

Answer

Can lead to Pneumatocele in some cases.

Answer

Primarily infects immunocompromised individuals.

Question 10

Which of the following statements about Cryptococcus is false?

Accepted Answer

Urease negative

Answer

Urease positive

Answer

Primarily infects lung

Answer

Encapsulated yeast

Mycology — MCQs

Mycology — MCQs

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