Mycology Practice Questions

Q: What is the most common cause of persistent vaginal candidiasis despite appropriate antifungal therapy?

Non-albicans Candida species. ***Non-albicans Candida species*** - While *Candida albicans* is the most common cause of initial candidiasis, persistent or recurrent infections despite appropriate fluconazole therapy are often due to **non-albicans Candida species** like *C. glabrata* or *C. krusei*. - These species are inherently less susceptible or resistant to fluconazole, necessitating different antifungal treatments. *Azole-resistant C. albicans* - Although possible, **azole resistance in *C. albicans*** is less common than infection by intrinsically resistant non-albicans species as a cause of persistent symptoms after initial standard therapy. - Reduced susceptibility due to prior azole exposure or host factors can contribute, but it's not the primary mechanism behind most refractory cases. *Underlying diabetes mellitus* - **Diabetes mellitus** can predispose individuals to candidiasis and recurrence due to elevated glycogen content in vaginal epithelial cells and impaired immune response. However, it's a risk factor for *developing* candidiasis, not the direct cause of persistent infection despite *appropriate antifungal treatment*. - While diabetes can make infections harder to clear, the persistence after treatment usually points to an issue with the pathogen itself, or the treatment strategy. *Concomitant bacterial vaginosis* - **Bacterial vaginosis (BV)** can coexist with candidiasis, but it's a separate infection caused by an imbalance of vaginal bacteria and would typically not cause persistent candidiasis symptoms *despite antifungal treatment*. - BV symptoms (e.g., "fishy" odor, thin discharge) are distinct from candidiasis (e.g., itching, thick cottage cheese discharge), and treating BV alone would not resolve a fungal infection.

Q: A patient in the ICU with a central venous catheter (CVC) develops an infection. Microscopy reveals ovoid budding yeast cells. What is the most likely organism?

Candida. ***Candida*** - **Gram-positive ovoid budding organisms** are characteristic findings for yeast, with **Candida** species being the most common cause of CVC-related fungal infections in ICU patients. - Patients with CVCs are at high risk for candidemia due to compromised skin barriers and often receiving broad-spectrum antibiotics, which can disrupt the normal flora. *Staphylococcus epidermidis* - This is a **Gram-positive coccus** that grows in clusters and is a common cause of CVC-related **bacterial infections**, developing **biofilms** on catheters. - It does not present as an ovoid budding organism on microscopy. *Escherichia coli* - This is a **Gram-negative rod**, typically associated with **urinary tract infections** and sepsis from an abdominal source. - It would not appear as a Gram-positive ovoid budding organism and is not a common cause of primary CVC-related bloodstream infections unless there's an associated abdominal source. *Staphylococcus aureus* - This is a **Gram-positive coccus** that grows in grape-like clusters and can cause severe CVC-related bloodstream infections, often leading to **endocarditis** or widespread dissemination. - Like *S. epidermidis*, it is a bacterium and does not exhibit ovoid budding.

Q: Broad-based budding yeasts are seen in:

Blastomycosis. ***Blastomycosis*** - This fungal infection is classically characterized by **broad-based budding yeasts** seen on microscopic examination. - The yeast cells are typically large and have a characteristic wide connection between the mother and daughter cells during budding. *Histoplasmosis* - Characterized by **small, intracellular yeasts** often seen within macrophages. - These yeasts do **not exhibit broad-based budding**. *Candidiasis* - Primarily presents as **pseudohyphae** (elongated yeast cells resembling hyphae) and budding yeasts (blastoconidia) with **narrow bases**. - **True hyphae** may also be present depending on the species and growth conditions. *Coccidioidomycosis* - In tissue, it is characterized by **spherules** containing **endospores**, not budding yeasts. - The mycelial form is found in culture or environmental samples.

Q: Desert rheumatism is caused by:

Coccidioides immitis. ***Coccidioides immitis*** - This fungus is the causative agent of **coccidioidomycosis**, also known as **Valley fever** or **desert rheumatism**, due to its prevalence in arid regions. - Infection most commonly occurs through inhalation of **arthroconidia** from disturbed soil in endemic areas. *Paracoccidioides brasiliensis* - This fungus causes **paracoccidioidomycosis** (South American blastomycosis), which is endemic to Latin America. - It typically manifests as chronic granulomatous disease affecting the lungs, skin, mucous membranes, lymph nodes, and internal organs. *Candida albicans* - This is a common opportunistic yeast responsible for various infections, from **superficial mucocutaneous candidiasis** (e.g., thrush, vaginal yeast infections) to severe invasive candidemia. - It is not associated with "desert rheumatism." *Cryptococcus neoformans* - This encapsulated yeast is a major cause of **cryptococcosis**, particularly in immunocompromised individuals. - It commonly causes **meningoencephalitis** and pulmonary disease, and is associated with bird droppings, but not "desert rheumatism."

Q: A hair perforation test was performed on a yeast isolate, and the result was positive. Which of the following organisms is associated with a positive hair perforation test?

Candida albicans. ***Candida albicans*** - The **hair perforation test** is a classic diagnostic test specifically used to identify *Candida albicans*, which characteristically produces **conical projections** when incubated with sterilized blonde hair in water at room temperature. - This test has historically been used as a simple, rapid method for **presumptive identification** of *C. albicans* from other Candida species, indicating the organism's ability to produce **keratinolytic enzymes**. *Candida tropicalis* - *Candida tropicalis* gives a **negative hair perforation test** and does not produce the characteristic hair perforations seen with *C. albicans*. - While it can form **pseudohyphae** and true hyphae, it can be differentiated from *C. albicans* using this test among others. *Candida glabrata* - *Candida glabrata* does **NOT** produce a positive hair perforation test and typically remains in **yeast form**. - It is distinguished from other Candida species by its **smaller cell size** and inability to form germ tubes or hair perforations. *Candida parapsilosis* - *Candida parapsilosis* also gives a **negative hair perforation test** and does not produce hair perforations. - This species can form **pseudohyphae** but the hair perforation test helps distinguish it from *C. albicans*.

Q: A man has undergone renal transplant and is taking immunosuppressant drug. On biopsy there was presence of budding cells with pseudohyphae. Identify the organism?

Invasive candidiasis. ***Invasive candidiasis*** - The presence of **budding cells** and **pseudohyphae** on biopsy is a classic histological finding for *Candida* species. - Individuals who have undergone **renal transplant** and are on **immunosuppressant drugs** are at high risk for opportunistic fungal infections, including invasive candidiasis. *Pneumocystis* - *Pneumocystis jirovecii* typically causes pneumonia and is characterized by cysts or trophic forms in lung tissue, not budding cells and pseudohyphae. - While common in immunocompromised patients, its microscopic morphology is distinctly different from *Candida*. *Invasive aspergillosis* - *Aspergillus* species are characterized by **septate hyphae with acute angle branching** (typically 45-degree angles) on microscopy. - They do not form budding cells or pseudohyphae, which are characteristic of *Candida*. *Histoplasmosis* - *Histoplasma capsulatum* appears as **small, oval-shaped yeast cells** (2-4 µm) often found within macrophages. - It does not form pseudohyphae or large budding cells as described in the question.

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.

Question 1

What is the most common cause of persistent vaginal candidiasis despite appropriate antifungal therapy?

Accepted Answer

Non-albicans Candida species

Answer

Azole-resistant C. albicans

Answer

Underlying diabetes mellitus

Answer

Concomitant bacterial vaginosis

Question 2

A patient in the ICU with a central venous catheter (CVC) develops an infection. Microscopy reveals ovoid budding yeast cells. What is the most likely organism?

Accepted Answer

Candida

Answer

Staphylococcus epidermidis

Answer

Escherichia coli

Answer

Staphylococcus aureus

Question 3

Broad-based budding yeasts are seen in:

Accepted Answer

Blastomycosis

Answer

Histoplasmosis

Answer

Candidiasis

Answer

Coccidioidomycosis

Question 4

Desert rheumatism is caused by:

Accepted Answer

Coccidioides immitis

Answer

Paracoccidioides brasiliensis

Answer

Candida albicans

Answer

Cryptococcus neoformans

Question 5

A hair perforation test was performed on a yeast isolate, and the result was positive. Which of the following organisms is associated with a positive hair perforation test?

Accepted Answer

Candida albicans

Answer

Candida tropicalis

Answer

Candida glabrata

Answer

Candida parapsilosis

Question 6

A forest worker developed skin lesions over the forearm, which initially started as macules but then became nodules. Histology of the nodule shows the following findings. Which of the following is true regarding this condition?

Accepted Answer

It is a dematiaceous fungus

Answer

Angioinvasion is common especially in people with hemolytic anemia

Answer

These bodies are formed by engulfment of the dead fungi by the macrophages

Answer

Infection commonly spreads to involve tendon, muscle and bone

Question 7

A man has undergone renal transplant and is taking immunosuppressant drug. On biopsy there was presence of budding cells with pseudohyphae. Identify the organism?

Accepted Answer

Invasive candidiasis

Answer

Pneumocystis

Answer

Invasive aspergillosis

Answer

Histoplasmosis

Question 8

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 9

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 10

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

Mycology — MCQs

Mycology — MCQs

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