Mycology Practice Questions

Q: Identify the correct 'organism-drug to which it is intrinsically resistant' pair.

Candida krusei - Fluconazole. ***Candida krusei - Fluconazole*** - **Candida krusei** is intrinsically resistant to **fluconazole** due to reduced affinity of its target enzyme, **lanosterol 14-alpha demethylase**, for the drug. - This resistance is a natural characteristic of the species, meaning it is inherent and not acquired through exposure. *Aspergillus fumigatus - Micafungin* - **Aspergillus fumigatus** is generally susceptible to **micafungin**, an **echinocandin drug** that targets fungal cell wall synthesis. - While resistance can develop, it is not an intrinsic characteristic of *A. fumigatus* to micafungin. *Candida albicans - Amphotericin B* - **Candida albicans** is typically susceptible to **amphotericin B**, a polyene antifungal that binds to ergosterol in the fungal cell membrane. - Intrinsic resistance to amphotericin B in *C. albicans* is rare, though acquired resistance can occur. *Aspergillus niger - Voriconazole* - **Aspergillus niger** is usually susceptible to **voriconazole**, a broad-spectrum triazole antifungal. - There is no known intrinsic resistance of *A. niger* to voriconazole.

Q: A fungal culture shows 'rising sun' pattern. Which microscopic finding would confirm Microsporum canis?

Banana-shaped macroconidia. ***Banana-shaped macroconidia*** - The 'rising sun' colonial pattern on fungal culture is characteristic of *Microsporum canis*, and the key microscopic feature confirming this diagnosis is the presence of **spindle-shaped** or **banana-shaped macroconidia** with rough, thick walls. - These macroconidia typically have 6-15 cells and are observed upon microscopic examination of the fungal culture. *Spiral hyphae* - **Spiral hyphae** are a characteristic microscopic feature seen in *Trichophyton mentagrophytes*, not typically in *Microsporum canis*. - They are coiled or corkscrew-like hyphal structures. *Racquet hyphae* - **Racquet hyphae** are microscopic structures with a swollen, club-shaped end resembling a tennis racquet, often found in various dermatophytes but not specifically diagnostic for *Microsporum canis*. - They are considered a less specific morphological feature. *Chlamydospores* - **Chlamydospores** are thick-walled, asexual spores that are resistant to adverse conditions and are commonly seen in other fungi, such as *Candida albicans* (especially terminal chlamydospores), but not a distinguishing feature for *Microsporum canis*. - They are a survival form of the fungus.

Q: A fungal culture shows 'slide culture' with 'match stick' appearance. Which microscopic finding would confirm Sporothrix schenckii?

Rosette of conidia. ***Rosette of conidia*** - The distinctive "rosette of conidia" or **"flowerette"** arrangement of conidia around the conidiophores is a classic microscopic feature of *Sporothrix schenckii* in culture. - This morphology, combined with the "matchstick" appearance on slide culture, is highly characteristic for identifying this dimorphic fungus. *Flower vase arrangement* - While *Sporothrix schenckii* can have conidia arranged in a flower-like pattern, the specific term "flower vase arrangement" is not the standard or most precise descriptor for its characteristic morphology. - The more accurate and commonly used term describing the conidia arrangement is **"rosette"** or "flowerette" of conidia. *Palisading hyphae* - **Palisading hyphae** refer to hyphae arranged in a fence-like or parallel alignment, which is not a characteristic microscopic feature of *Sporothrix schenckii*. - This morphology might be seen in other fungal species but does not help in identifying *Sporothrix schenckii*. *Ship-in-bottle appearance* - The "ship-in-bottle" appearance is a microscopic characteristic associated with **Exophiala species**, particularly *Exophiala jeanselmei*. - This morphology involves conidia forming along the sides of hyphae, resembling small cells within a vessel, and is not seen in *Sporothrix schenckii*.

Q: A fungal culture shows powdery colonies with radial grooves on Sabouraud's agar. Which microscopic finding would most specifically confirm dermatophyte infection?

Spiral hyphae. ***Spiral hyphae*** - **Spiral hyphae** are a specific and characteristic microscopic finding in dermatophytes, particularly *Trichophyton mentagrophytes* - These coiled/spiral structures are diagnostic features that help differentiate dermatophytes from other fungal infections - Along with macroconidia and microconidia arrangement, spiral hyphae are key identifying features in dermatophyte culture *Microconidia in grape-like clusters* - While microconidia are present in dermatophytes, the grape-like cluster arrangement (**en grappe**) is seen in various dermatophyte species but is less specific than spiral hyphae - *Microsporum* species show microconidia in different arrangements, but this finding alone is not as diagnostically specific *Broader angle branching* - **Broader angle branching** (usually >45 degrees, often 90 degrees) with ribbon-like, non-septate hyphae is characteristic of **Mucorales** (e.g., *Rhizopus*, *Mucor*) - These are opportunistic molds causing mucormycosis in immunocompromised patients, not dermatophyte infections - Structurally and clinically distinct from dermatophytes *Yeast with pseudohyphae* - **Yeast with pseudohyphae** is the classic microscopic finding for **Candida species** - *Candida* causes superficial candidiasis, not dermatophyte infections (dermatophytosis/tinea) - Dermatophytes are filamentous fungi, not yeasts

Q: A fungal culture shows 'flower vase' arrangement of macroconidia. Which microscopic feature would confirm Fusarium species?

Banana-shaped macroconidia. ***Banana-shaped macroconidia*** - The presence of **canoe- or banana-shaped macroconidia** found in a "flower vase" arrangement (sporodochium) is a definitive microscopic characteristic of *Fusarium species*. - These distinctive macroconidia distinguish *Fusarium* from other filamentous fungi. *Chlamydospores* - **Chlamydospores** are thick-walled, asexual spores that can be found in various fungi, including *Candida albicans* and some *Fusarium* species. - However, they are not the primary or most distinctive feature for confirming *Fusarium* species, especially compared to the morphology of its macroconidia. *Racquet hyphae* - **Racquet hyphae** are hyphae with swollen, club-shaped cells at their ends, resembling a tennis racquet. - These are characteristic of dermatophytes, such as *Trichophyton rubrum*, and are not typically seen as a defining feature of *Fusarium*. *Ship-in-bottle appearance* - The "ship-in-bottle" appearance refers to the characteristic morphology of **arthroconidia** in *Coccidioides immitis*, seen in tissue or culture. - This feature is specific to *Coccidioides* and is not associated with *Fusarium species*.

Q: A sputum culture shows colonies with 'corn flakes' appearance and distinctive musty earth odor. Which microscopic finding would confirm Aspergillus fumigatus?

Septate hyphae with 45-degree branching. ***Septate hyphae with 45-degree branching*** - The distinctive **'corn flakes' appearance** and **musty earth odor** in sputum culture are classic macroscopic findings for *Aspergillus fumigatus*. - Microscopically, *Aspergillus* species are characterized by **septate hyphae** that exhibit a characteristic **45-degree (acute-angle) branching** pattern. *Broad aseptate hyphae* - This morphology is characteristic of **Zygomycetes** (e.g., *Rhizopus*, *Mucor*), which cause mucormycosis. - These fungi typically show **non-septate** or sparsely septate hyphae with **irregular, wide-angle branching**. *Dematiaceous hyphae* - This term refers to **pigmented (dark-walled) hyphae** and is characteristic of various fungi that cause phaeohyphomycosis. - *Aspergillus* species are generally considered **hyaline (clear-walled)** fungi. *Pseudohyphae with blastoconidia* - This microscopic appearance is typical of **yeasts like *Candida albicans***, which form **pseudohyphae** (elongated yeast cells that resemble hyphae) and **blastoconidia** (yeast buds). - *Aspergillus* is a mold that forms true hyphae, not pseudohyphae.

Q: A skin scraping from a patient with hypopigmented patches shows fungal elements on KOH mount. Which microscopic finding would confirm Malassezia furfur infection?

Short hyphae with narrow-based budding yeast cells. ***Short hyphae with narrow-based budding yeast cells*** - The classic "**spaghetti and meatballs**" appearance on KOH mount for *Malassezia furfur* primarily consists of **short, stubby hyphae** and clustered **budding yeast cells**, specifically with a narrow base. - This morphology is pathognomonic for **pityriasis versicolor** and related *Malassezia* infections. *Septate hyphae* - While many dermatophytes and other fungi exhibit **septate hyphae**, this term alone is too general and does not specifically identify *Malassezia furfur*. - It would not differentiate *Malassezia* from other fungal infections that also present with septate hyphae. *Short, stout hyphae with arthroconidia* - This description is more typical of **dermatophytes** like *Trichophyton* or *Epidermophyton*, which cause tinea infections. - **Arthroconidia** are characteristic asexual spores of dermatophytes, not *Malassezia furfur*. *Curved hyphae with banana-shaped macroconidia* - This morphology is characteristic of **dermatophytes** in the genus *Microsporum*, particularly *Microsporum canis*. - This finding would indicate a **tinea corporis** or **tinea capitis** infection, not a *Malassezia* infection.

Q: Microsporum involves:

Skin and hair. ***Skin and hair*** - *Microsporum* species are **dermatophytes** that commonly cause superficial fungal infections - They have a particular predilection for keratinized tissues like **skin and hair**, leading to conditions such as **tinea capitis** (scalp ringworm) and **tinea corporis** (body ringworm) - This is the characteristic pattern for *Microsporum* species including *M. canis*, *M. audouinii*, and *M. gypseum* *Skin and nails* - While *Microsporum* can affect the skin, its involvement with **nails (onychomycosis)** is extremely rare - Nail infections are typically associated with **Trichophyton rubrum** or **T. mentagrophytes**, not *Microsporum* *Hair and nails* - **Nail involvement** is not a characteristic of *Microsporum* infections - The main sites of infection are hair and smooth skin, not nails *Skin, hair and nails* - Including **nails** as a site for *Microsporum* is inaccurate; its primary targets are skin and hair only - While some dermatophytes (like *Trichophyton*) can affect all three tissues, *Microsporum* has specific tropism for skin and hair

Q: Otomycosis is most commonly caused by:

Aspergillus fumigatus. ***Aspergillus fumigatus*** - **Aspergillus species**, particularly *A. fumigatus* and *A. niger*, are the most frequent causes of **otomycosis**, accounting for 80-90% of cases. - They thrive in damp, warm environments, making the external auditory canal an ideal site for their growth, often presenting with a **black or grayish fungal debris**. *Mucor* - **Mucor** is a less common cause of otomycosis and is more often associated with **rhinocerebral mucormycosis** in immunocompromised individuals. - While it can cause opportunistic infections, its prevalence in otomycosis is significantly lower compared to Aspergillus. *Actinomycetes* - **Actinomycetes** are **filamentous bacteria**, not fungi, and are typically associated with **actinomycosis**, a chronic suppurative infection. - They are known to cause infections in the head and neck, but not typically otomycosis, which is a fungal infection of the ear. *Candida albicans* - **Candida albicans** is the second most common cause of otomycosis, but it is less prevalent than Aspergillus species. - Infections by Candida tend to be more common in individuals with a history of **antibiotic use** or in **immunocompromised patients**, and often present with a *creamy white discharge*.

Question 1

Identify the correct 'organism-drug to which it is intrinsically resistant' pair.

Accepted Answer

Candida krusei - Fluconazole

Answer

Candida albicans - Amphotericin B

Answer

Aspergillus fumigatus - Micafungin

Answer

Aspergillus niger - Voriconazole

Question 2

A 34-year-old woman presents with multiple round, scaly patches on her chest and back. The lesions are hypopigmented and slightly pruritic. KOH preparation of skin scrapings shows short, angular hyphae. Which of the following best describes the causative organism's morphology in culture?

Accepted Answer

Branching, septate hyphae with characteristic 'spaghetti and meatballs' appearance

Answer

Non-septate hyphae with sporangiospores

Answer

Branching, septate hyphae with tear-drop microconidia

Answer

Pseudohyphae with blastoconidia

Question 3

A fungal culture shows 'rising sun' pattern. Which microscopic finding would confirm Microsporum canis?

Accepted Answer

Banana-shaped macroconidia

Answer

Spiral hyphae

Answer

Racquet hyphae

Answer

Chlamydospores

Question 4

A fungal culture shows 'slide culture' with 'match stick' appearance. Which microscopic finding would confirm Sporothrix schenckii?

Accepted Answer

Rosette of conidia

Answer

Flower vase arrangement

Answer

Palisading hyphae

Answer

Ship-in-bottle appearance

Question 5

A fungal culture shows powdery colonies with radial grooves on Sabouraud's agar. Which microscopic finding would most specifically confirm dermatophyte infection?

Accepted Answer

Spiral hyphae

Answer

Microconidia in grape-like clusters

Answer

Broader angle branching

Answer

Yeast with pseudohyphae

Question 6

A fungal culture shows 'flower vase' arrangement of macroconidia. Which microscopic feature would confirm Fusarium species?

Accepted Answer

Banana-shaped macroconidia

Answer

Chlamydospores

Answer

Racquet hyphae

Answer

Ship-in-bottle appearance

Question 7

A sputum culture shows colonies with 'corn flakes' appearance and distinctive musty earth odor. Which microscopic finding would confirm Aspergillus fumigatus?

Accepted Answer

Septate hyphae with 45-degree branching

Answer

Broad aseptate hyphae

Answer

Dematiaceous hyphae

Answer

Pseudohyphae with blastoconidia

Question 8

A skin scraping from a patient with hypopigmented patches shows fungal elements on KOH mount. Which microscopic finding would confirm Malassezia furfur infection?

Accepted Answer

Short hyphae with narrow-based budding yeast cells

Answer

Septate hyphae

Answer

Short, stout hyphae with arthroconidia

Answer

Curved hyphae with banana-shaped macroconidia

Question 9

Microsporum involves:

Accepted Answer

Skin and hair

Answer

Skin and nails

Answer

Hair and nails

Answer

Skin, hair and nails

Question 10

Otomycosis is most commonly caused by:

Accepted Answer

Aspergillus fumigatus

Answer

Mucor

Answer

Actinomycetes

Answer

Candida albicans

Mycology — MCQs

Mycology — MCQs

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