Mycology Practice Questions

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: 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*.

Q: Which of the following fungi is difficult to isolate in culture?

Malassezia furfur. ***Malassezia furfur*** - *Malassezia furfur* is a **lipophilic fungus**, meaning it requires lipids (fatty acids) for growth, making it difficult to isolate on standard culture media. - Its requirement for **exogenous fatty acids** is a key reason for its fastidious nature in laboratory culture. *Candida* - **Candida species** are relatively easy to grow on standard mycological media like Sabouraud dextrose agar (SDA) and blood agar. - They are **opportunistic yeasts** that form creamy, smooth colonies, readily identifiable in routine clinical microbiology. *Cryptococcus* - **Cryptococcus neoformans** and *gatti* can be cultured using standard mycological media (e.g., SDA) and selective media like birdseed (Niger seed) agar, which helps in its identification due to melanin production. - They are known for their **capsule production**, a key virulence factor, and can be easily visualized in clinical specimens with India ink stain. *Dermatophytes* - **Dermatophytes** (e.g., *Trichophyton*, *Microsporum*, *Epidermophyton*) grow well on Sabouraud dextrose agar, often with the addition of antibiotics to inhibit bacterial growth. - Their ability to **colonize keratinized tissues** (skin, hair, nails) is characteristic, and they are not considered fastidious in culture.

Q: A farmer presents you with a cauliflower-shaped mass on foot, which developed after a minor injury. Microscopy shows copper penny bodies. What is the most likely diagnosis?

Chromoblastomycosis. **Chromoblastomycosis** - The characteristic "cauliflower-shaped" lesion on the foot following a minor injury, especially in a farmer (indicating outdoor exposure), is highly suggestive of chromoblastomycosis. - The presence of **copper penny bodies** (also known as **sclerotic** or **muriform cells**) on microscopy is **pathognomonic** for chromoblastomycosis. *Blastomycosis* - Blastomycosis typically presents with **granulomatous lesions** that can ulcerate but are rarely described as cauliflower-shaped. - Microscopic examination would reveal **broad-based budding yeast cells**, not copper penny bodies. *Sporotrichosis* - Sporotrichosis usually presents as **subcutaneous nodules** that can ulcerate and spread lymphatically, forming a chain of lesions. - Microscopy shows **cigar-shaped budding yeasts** within macrophages or neutrophils, which are distinct from copper penny bodies. *Phaeohyphomycosis* - Phaeohyphomycosis encompasses a broad group of infections by dematiaceous fungi that produce **dark-walled hyphae** or yeast-like cells in tissue. - While it can cause subcutaneous nodules or cysts, the presence of distinct copper penny bodies points away from phaeohyphomycosis as the primary diagnosis.

Q: Fungal infection which is acquired by traumatic inoculation is?

Sporothrix. ***Sporothrix*** - **Sporotrichosis** is characteristically acquired through **traumatic inoculation** of the fungus, often from contact with soil, thorns, or decaying vegetation. - The organism causes **cutaneous lymphatic disease**, presenting as nodular lesions along lymphatic drainage paths. *Blastomyces* - **Blastomycosis** is typically acquired by inhaling airborne fungal spores, usually from **soil rich in organic matter** or decaying wood. - It primarily affects the **lungs** and can disseminate to the skin, bones, and other organs, but is not primarily associated with traumatic inoculation. *Coccidioides* - **Coccidioidomycosis** (Valley Fever) is acquired by inhaling **arthroconidia** present in dust or soil in endemic areas. - It is a **pulmonary infection** that can disseminate to other body sites, and its entry is almost exclusively respiratory, not traumatic. *Paracoccidioides* - **Paracoccidioidomycosis** is acquired by inhaling airborne fungal propagules, typically found in **soil in Latin America**. - It primarily causes **chronic pulmonary disease** and can spread to mucous membranes, skin, and lymph nodes, with no known association with traumatic inoculation.

Q: Which fungus is most commonly associated with orbital cellulitis in patients with diabetic ketoacidosis?

Rhizopus. ***Rhizopus*** - *Rhizopus* is the most common cause of **mucormycosis** (also called zygomycosis), an aggressive fungal infection that frequently affects immunocompromised patients, especially those with **diabetic ketoacidosis (DKA)**. - *Rhizopus arrhizus* (formerly *R. oryzae*) accounts for approximately **70% of all mucormycosis cases**, making it the single most common causative organism. - In DKA, the acidic environment and high glucose levels favor the growth of **Mucorales fungi**, leading to rapid progression from the sinuses to the orbit and brain (rhinoorbital-cerebral mucormycosis). *Candida* - While *Candida* is a common cause of fungal infections, it typically manifests as **candidemia**, **esophagitis**, or **vulvovaginitis**, and is rarely associated with orbital cellulitis in DKA. - *Candida* infections are more likely in patients with indwelling catheters or those on broad-spectrum antibiotics, rather than specifically linked to DKA-induced orbital cellulitis. *Mucor* - The genus *Mucor* is part of the **Mucorales order** and can cause **mucormycosis** with identical clinical presentations to *Rhizopus*. - However, *Mucor* species account for only **10-20% of mucormycosis cases**, making *Rhizopus* the **most commonly** associated genus as asked in the question. - While both are clinically grouped under "mucormycosis," *Rhizopus* is the more specific and statistically correct answer when identifying the most common causative fungus. *Aspergillus* - *Aspergillus* species are common environmental fungi that can cause invasive infections, particularly in immunocompromised patients, leading to conditions like **aspergilloma** or **invasive aspergillosis**. - While *Aspergillus* can cause sinus and orbital infections, it is less commonly associated with the rapid, aggressive form of orbital cellulitis seen in DKA compared to mucormycosis caused by *Rhizopus*.

Q: Pneumocystis jirovecii, typically seen in immunocompromised patients, is a:

Fungus. ***Fungus*** - *Pneumocystis jirovecii* is a **yeast-like fungus** that causes severe lung infections, particularly in individuals with **compromised immune systems**, such as those with HIV/AIDS. - Its classification has evolved, but it is now firmly established as a fungus based on its **genetic makeup** and cell wall structure. *Bacteria* - Bacteria are single-celled microorganisms that belong to the kingdom **Prokaryotae**, lacking a true nucleus and membrane-bound organelles. - While bacteria can cause pneumonia in immunocompromised patients, *Pneumocystis jirovecii* has a distinct **eukaryotic cell structure** and genetic characteristics of fungi. *Virus* - Viruses are **acellular infectious agents** that replicate only inside the living cells of other organisms. - Viruses cause a wide range of infections, but *Pneumocystis jirovecii* possesses its own **cellular machinery** and metabolic pathways, classifying it outside the viral domain. *Parasite* - Parasites are organisms that live on or in a host organism and obtain their food at the expense of their host. - Although *Pneumocystis jirovecii* was historically misclassified as a protozoan parasite due to its morphology, molecular studies have since confirmed its **fungal lineage**.

Q: Which of the following statements about Penicillium marneffei is incorrect?

Forms black colonies. ***Forms black colonies*** - *Penicillium marneffei* typically forms colonies that are often **reddish-beige** or **pigmented red-diffusible**, not black. - The production of a characteristic **red-to-burgundy pigment** is a key identifying feature of this fungus, especially in culture. *Is a dimorphic fungus* - This statement is correct. *Penicillium marneffei* is a **thermally dimorphic fungus**, meaning it grows as a mould at 25°C (room temperature) and as yeast-like cells at 37°C (body temperature). - This dimorphism is crucial for its pathogenesis and identification. *Amphotericin B is used for treatment* - This statement is correct. **Amphotericin B** is a commonly used antifungal agent for the treatment of severe *Penicillium marneffei* infections, particularly in immunocompromised patients. - It is often followed by a maintenance regimen with an azole antifungal like itraconazole. *Causes severe infections in immunocompromised patients* - This statement is correct. *Penicillium marneffei* is an **opportunistic pathogen** that primarily causes severe, disseminated infections in individuals with compromised immune systems, especially those with HIV/AIDS. - Endemic regions include Southeast Asia, where it is a leading cause of systemic mycosis in HIV-positive patients.

Question 1

What is the primary component that dermatophytes infect?

Accepted Answer

Keratin

Answer

Epidermis

Answer

Hair

Answer

Nails

Question 2

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 3

Which of the following statements about Cryptococcus is false?

Accepted Answer

Urease negative

Answer

Urease positive

Answer

Primarily infects lung

Answer

Encapsulated yeast

Question 4

Which of the following fungi is difficult to isolate in culture?

Accepted Answer

Malassezia furfur

Answer

Candida

Answer

Cryptococcus

Answer

Dermatophytes

Question 5

A farmer presents you with a cauliflower-shaped mass on foot, which developed after a minor injury. Microscopy shows copper penny bodies. What is the most likely diagnosis?

Accepted Answer

Chromoblastomycosis

Answer

Sporotrichosis

Answer

Blastomycosis

Answer

Phaeohyphomycosis

Question 6

Fungal infection which is acquired by traumatic inoculation is?

Accepted Answer

Sporothrix

Answer

Coccidioides

Answer

Paracoccidioides

Answer

Blastomyces

Question 7

Which fungus is most commonly associated with orbital cellulitis in patients with diabetic ketoacidosis?

Accepted Answer

Rhizopus

Answer

Candida

Answer

Mucor

Answer

Aspergillus

Question 8

Pneumocystis jirovecii, typically seen in immunocompromised patients, is a:

Accepted Answer

Fungus

Answer

Parasite

Answer

Virus

Answer

Bacteria

Question 9

Which of the following statements about Penicillium marneffei is incorrect?

Accepted Answer

Forms black colonies

Answer

Is a dimorphic fungus

Answer

Amphotericin B is used for treatment

Answer

Causes severe infections in immunocompromised patients

Question 10

Which of the following statements is true regarding dimorphic fungi?

Accepted Answer

Transforms between yeast and mold forms at different temperatures

Answer

Exists in two distinct morphological forms

Answer

All dimorphic fungi are highly pathogenic to immunocompetent hosts

Answer

Primarily found in tropical and subtropical regions

Mycology — MCQs

Mycology — MCQs

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