Fungal Infections — MCQs
A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?
Wood's Lamp is used in the diagnosis of:
A 27-year-old intravenous drug user presents with difficulty swallowing. Examination of the oropharynx reveals white plaques along the tongue and the oral mucosa. Which of the following best describes the microscopic appearance of the microorganism responsible for this patient's illness?
Histoplasma capsulatum, a dimorphic fungus found in soil heavily contaminated with bird droppings, is identified in tissue biopsies by which of the following characteristics?
Regarding fungal cell wall, all are true except:
A biopsy of a lung nodule from a patient with a history of bird exposure reveals yeast cells with thick capsules. What is the most likely pathogen?
An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?
Amphotericin B toxicity can be lowered by:
Which of the following classifications correctly describes fungi?
An 34-year-old male HIV patient on c-A presents with seizures and a unilateral facial nerve palsy. The CT scan shows a ring-enhancing lesion. What is the best treatment?
Fungal Infections Indian Medical PG Practice Questions and MCQs
Question 1: A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?
- A. Candida albicans
- B. Cryptococcus neoformans (Correct Answer)
- C. Histoplasma capsulatum
- D. Coccidioides immitis
Explanation: ***Cryptococcus neoformans*** - This fungus is a common cause of **meningitis in AIDS patients** and characteristically appears as **encapsulated yeasts** on India ink staining of CSF. - The capsule excludes the ink, creating a distinct **halo** around the yeast cell, which is diagnostic. *Candida albicans* - While *Candida* can cause systemic infections, including meningitis, it typically presents as **pseudohyphae** or budding yeast without an obvious capsule on India ink stain. - *Candida meningitis* is less common in AIDS patients compared to *Cryptococcus*. *Histoplasma capsulatum* - This is a dimorphic fungus that causes **histoplasmosis**, often disseminated in AIDS patients, but typically manifests as **pulmonary disease** or hepatosplenomegaly. - It appears as small, **intracellular yeasts** within macrophages and would not show an encapsulated form on India ink stain in CSF. *Coccidioides immitis* - This dimorphic fungus causes **coccidioidomycosis**, which can lead to meningitis, particularly in immunocompromised individuals. - In CSF, it is seen as **spherules containing endospores**, not encapsulated yeasts, which is a distinct morphological feature.
Question 2: Wood's Lamp is used in the diagnosis of:
- A. Pityriasis versicolor (Correct Answer)
- B. Tinea pedis
- C. Sporotrichosis
- D. All of the options
Explanation: ***Pityriasis versicolor*** - A Wood's lamp is used to diagnose **Pityriasis versicolor** as the affected areas fluoresce a characteristic **golden yellow** (sometimes yellow-green) color due to the presence of porphyrins produced by the Malassezia fungus. - This diagnostic tool helps in visualizing subtle lesions and confirming the diagnosis of this superficial fungal infection. *Tinea pedis* - **Tinea pedis**, or athlete's foot, is typically diagnosed clinically based on symptoms like **itching, scaling, and redness**, or through **potassium hydroxide (KOH) microscopy** of skin scrapings to visualize hyphae. - A Wood's lamp is generally **not useful** for Tinea pedis, as the causative dermatophytes usually do not fluoresce. *Sporotrichosis* - **Sporotrichosis** is a subcutaneous fungal infection usually diagnosed by **fungal culture** from lesional tissue or aspiration, and sometimes by **histopathology**. - A Wood's lamp is **not used** in the diagnosis of sporotrichosis as the Sporothrix schenckii fungus does not exhibit fluorescence under UV light. *All of the options* - This option is incorrect because a Wood's lamp is only reliably used for **Pityriasis versicolor** among the given choices, due to the characteristic fluorescence of the causative organism. - It does not aid in the diagnosis of **Tinea pedis** or **Sporotrichosis**.
Question 3: A 27-year-old intravenous drug user presents with difficulty swallowing. Examination of the oropharynx reveals white plaques along the tongue and the oral mucosa. Which of the following best describes the microscopic appearance of the microorganism responsible for this patient's illness?
- A. Budding yeast and pseudohyphae (Correct Answer)
- B. Encapsulated yeast
- C. Mold with nonseptate hyphae
- D. Mold with septate hyphae
Explanation: ***Budding yeast and pseudohyphae*** - The clinical presentation of **white plaques** in the oropharynx of an **IV drug user** strongly suggests **oral candidiasis** (thrush), caused by *Candida albicans*. - Microscopically, *Candida albicans* is characterized by **budding yeast** forms and the formation of **pseudohyphae** when invading tissues. *Encapsulated yeast* - This description typically refers to *Cryptococcus neoformans*, which is known for its **thick polysaccharide capsule**. - While *Cryptococcus* can cause infections in immunocompromised individuals, it typically presents with **meningitis** or **pulmonary disease**, not oral thrush. *Mold with nonseptate hyphae* - This morphology is characteristic of organisms causing **zygomycosis** (e.g., *Rhizopus*, *Mucor*). - These infections usually present as **rhinocerebral** or **pulmonary involvement** and are not associated with superficial oral plaques like those seen in this patient. *Mold with septate hyphae* - This describes many common molds, including *Aspergillus* species, which typically cause **invasive pulmonary disease**, **sinusitis**, or **allergic bronchopulmonary aspergillosis**. - These organisms are **not typically associated** with oral thrush and produce true hyphae with septations, unlike the pseudohyphae of *Candida*.
Question 4: Histoplasma capsulatum, a dimorphic fungus found in soil heavily contaminated with bird droppings, is identified in tissue biopsies by which of the following characteristics?
- A. Yeasts with broad-based buds
- B. Single-cell yeasts with pseudohyphae
- C. Arthrospores
- D. Oval budding yeasts within macrophages (Correct Answer)
Explanation: ***Oval budding yeasts within macrophages*** - In tissue biopsies, **Histoplasma capsulatum** characteristically appears as small, **oval-shaped budding yeasts** that are predominantly found **intracellularly within macrophages**. - This intracellular location is a key diagnostic feature, as the organism can survive and multiply inside these phagocytic cells. *Yeasts with broad-based buds* - This description is characteristic of **Blastomyces dermatitidis**, another dimorphic fungus, which displays large yeasts with a single broad-based bud in tissue. - Unlike *Histoplasma*, **Blastomyces** yeasts are typically much larger and not necessarily intracellular. *Single-cell yeasts with pseudohyphae* - This morphology is characteristic of **Candida albicans**, particularly in its pathogenic forms within tissues. - **Candida** forms true hyphae and pseudohyphae, and its yeasts do not typically reside within macrophages in the same manner as *Histoplasma*. *Arthrospores* - **Arthrospores** (also called arthroconidia) are characteristic of fungi like **Coccidioides immitis**, which appear as barrel-shaped structures in laboratory cultures, but *spherules containing endospores* are seen in tissue. - **Histoplasma** does not form arthrospores in human tissue; it forms yeasts.
Question 5: Regarding fungal cell wall, all are true except:
- A. Contains chitin
- B. Prevent osmotic damage
- C. Does not contain peptidoglycan
- D. Azoles act on them (Correct Answer)
Explanation: ***Azoles act on them*** - **Azole antifungals** primarily target the **ergosterol synthesis** pathway, specifically inhibiting the **lanosterol 14-alpha-demethylase** enzyme, which is located in the fungal cell membrane, not the cell wall. - While the cell wall is crucial for fungal viability, agents targeting it (e.g., **echinocandins**) are distinct from azoles. *Contains chitin* - The fungal cell wall is indeed a complex structure composed of various carbohydrates, with **chitin** being a major structural polysaccharide that provides rigidity. - Chitin is a **beta-(1,4)-linked polymer of N-acetylglucosamine** and is a unique component distinguishing fungal cells from animal cells. *Prevent osmotic damage* - The rigid fungal cell wall provides structural support and protects the cell from **environmental stresses**, particularly **osmotic lysis** in hypotonic environments. - It maintains the cell's integrity against internal **turgor pressure**, which is essential for fungal growth and survival. *Does not contain peptidoglycan* - Fungal cell walls are distinct from bacterial cell walls in their composition; they **do not contain peptidoglycan**. - **Peptidoglycan** is a characteristic component of bacterial cell walls, which is targeted by antibiotics like penicillins.
Question 6: A biopsy of a lung nodule from a patient with a history of bird exposure reveals yeast cells with thick capsules. What is the most likely pathogen?
- A. Aspergillus fumigatus
- B. Blastomyces dermatitidis
- C. Histoplasma capsulatum
- D. Cryptococcus neoformans (Correct Answer)
Explanation: ***Cryptococcus neoformans*** - The presence of **yeast cells with thick capsules** is a classic histological finding for *Cryptococcus neoformans*. - While *Cryptococcus* commonly affects immunocompromised individuals, it can also be found in **bird droppings**, particularly from pigeons, making the history of bird exposure relevant. *Aspergillus fumigatus* - *Aspergillus fumigatus* typically presents as **hyphae**, not yeast cells, and would not have a thick capsule. - Infections often manifest as **aspergillomas** (fungus balls) in lung cavities or invasive disease in immunocompromised patients. *Blastomyces dermatitidis* - *Blastomyces dermatitidis* appears as **large, broad-based budding yeast cells** but does not possess a thick capsule. - It is typically found in the **soil**, especially in moist areas, and its association with bird exposure is not as strong as with *Cryptococcus*. *Histoplasma capsulatum* - *Histoplasma capsulatum* is characterized by **small intracellular yeast forms** within macrophages and does not have a thick capsule. - It is strongly associated with **bird and bat droppings** but its microscopic appearance is distinct from that described.
Question 7: An 8-year-old male presents with multiple patches of alopecia and severe pruritus. A bright blue-green fluorescence is seen on examination of the scalp with a Wood's lamp. Pathogen most likely responsible is?
- A. Microsporum canis (Correct Answer)
- B. Epidermophyton floccosum
- C. Candida albicans
- D. Trichophyton tonsurans
Explanation: ***Microsporum canis*** - This dermatophyte species is a common cause of **tinea capitis** in children, characterized by **patches of alopecia** and **pruritus**. - **Microsporum** species are known to exhibit **bright blue-green fluorescence** under a Wood's lamp due to the production of pteridine, which aids in diagnosis. *Epidermophyton floccosum* - This fungus primarily causes **tinea pedis**, **tinea cruris**, and **tinea corporis**, but rarely **tinea capitis**. - Infections caused by *Epidermophyton floccosum* typically do **not fluoresce** under a Wood's lamp. *Candida albicans* - *Candida albicans* is a yeast that causes superficial infections like **oral thrush**, **diaper rash**, and **vaginitis**, but it is **not a common cause of tinea capitis**. - *Candida* infections do **not show fluorescence** with a Wood's lamp. *Trichophyton tonsurans* - This is a common cause of **tinea capitis** (especially in the US), often presenting as **"black dot" tinea capitis** due to hair shaft breakage at the scalp surface. - Infections by *Trichophyton tonsurans* typically do **not fluoresce** under a Wood's lamp, differentiating it from *Microsporum* infections.
Question 8: Amphotericin B toxicity can be lowered by:
- A. Using Liposomal delivery systems (Correct Answer)
- B. Reducing the dose
- C. Combining with flucytosine
- D. Administering with saline hydration
Explanation: ***Using Liposomal delivery systems*** - **Liposomal amphotericin B** significantly reduces toxicity by encapsulating the drug, thereby decreasing its direct contact with human cells, particularly kidney cells. - This delivery system allows for higher doses of amphotericin B to be administered with fewer side effects, especially **nephrotoxicity** and **infusion-related reactions**. - This is the **primary and most effective method** to lower amphotericin B toxicity while maintaining therapeutic efficacy. *Administering with saline hydration* - Hydration with **normal saline (0.9% NaCl)** is a general supportive measure during amphotericin B infusion to help mitigate **nephrotoxicity** by maintaining adequate renal perfusion. - While important for kidney protection and a standard adjunct to therapy, it does not directly alter drug-host cell interaction or intrinsic drug toxicity. - This is a supportive measure, not a primary method for lowering the systemic toxicity profile of the drug itself. *Reducing the dose* - While reducing the dose would lower toxicity, it would also likely compromise the **therapeutic efficacy** against severe fungal infections, which is often unacceptable given the life-threatening nature of these diseases. - This approach is generally reserved for situations where toxicity outweighs clinical benefit, necessitating a change in treatment strategy rather than a primary method for safe administration. *Combining with flucytosine* - Combining amphotericin B with **flucytosine** is a strategy to achieve a synergistic fungicidal effect and reduce the individual doses required, but flucytosine itself can have **bone marrow suppression** and other toxicities. - This combination enhances antifungal efficacy and can allow for *lower doses of amphotericin B*, indirectly reducing its toxicity, but it introduces the toxicity profile of flucytosine and is not a direct method to *lower amphotericin B's intrinsic toxicity*.
Question 9: Which of the following classifications correctly describes fungi?
- A. Prokaryotic organisms
- B. Eukaryotic organisms (Correct Answer)
- C. Multicellular organisms
- D. Unicellular organisms
Explanation: ***Eukaryotic organisms*** - Fungi possess a **true nucleus** enclosed within a nuclear membrane and **membrane-bound organelles** like mitochondria and endoplasmic reticulum. - Their cells have a complex internal structure, distinguishing them from prokaryotes. *Prokaryotic organisms* - **Prokaryotes** lack a true nucleus and membrane-bound organelles; their genetic material is free in the cytoplasm. - Examples of prokaryotes include **bacteria** and archaea, not fungi. *Multicellular organisms* - While many fungi are **multicellular** (e.g., mushrooms), some are **unicellular** (e.g., yeasts), so this classification is not universally descriptive. - Thus, classifying all fungi solely as multicellular would be inaccurate. *Unicellular organisms* - While some fungi, such as **yeasts**, are unicellular, many others, like **molds** and mushrooms, are multicellular. - Therefore, classifying all fungi as unicellular is an **incomplete** description.
Question 10: An 34-year-old male HIV patient on c-A presents with seizures and a unilateral facial nerve palsy. The CT scan shows a ring-enhancing lesion. What is the best treatment?
- A. Albendazole with dexamethasone
- B. Amphotericin B
- C. ATT with steroids
- D. Sulphadiazine, pyrimethamine and Leucovorin (Correct Answer)
Explanation: ***Sulphadiazine, pyrimethamine and Leucovorin*** - This combination is the standard **first-line treatment for cerebral toxoplasmosis**, which is strongly suggested by the clinical presentation (HIV patient, seizures, facial nerve palsy) and the imaging findings of **multiple ring-enhancing lesions**. - **Leucovorin** is added to prevent bone marrow suppression caused by pyrimethamine. *Albendazole with dexamethasone* - **Albendazole** is primarily used for **neurocysticercosis**, which typically presents with cystic lesions, not necessarily ring-enhancing, and the patient's HIV status makes toxoplasmosis more likely. - While **dexamethasone** may be used to reduce brain edema, it's adjunctive and not the primary antimicrobial treatment for toxoplasmosis. *Amphotericin B* - **Amphotericin B** is the mainstay treatment for **cryptococcal meningitis** and other severe fungal infections, which usually present with symptoms of meningitis and different imaging findings (e.g., hydrocephalus, gelatinous pseudocysts). - It is not effective against **Toxoplasma gondii**. *ATT with steroids* - **ATT (Anti-Tubercular Therapy)** with steroids is the treatment for **CNS tuberculosis**, which can present with ring-enhancing lesions. - However, the typical presentation for CNS tuberculosis in HIV patients often includes basilar meningitis, multiple tuberculomas, or abscesses, and toxoplasmosis is a far more common cause of ring-enhancing lesions in HIV patients with CD4 counts < 100 cells/µL.
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