A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of the following organisms is the most likely causative agent?

1. A

   A. Aspergillus fumigatus

2. B

   B. Pneumocystis jirovecii

3. C

   C. Histoplasma capsulatum

4. D

   D. Cryptococcus neoformans

Appeared in: INI-CET EXAM -2026

Explanation

• Cryptococcus neoformans is a well-known encapsulated yeast that is a leading cause of fungal meningitis, particularly in individuals with compromised immune systems.
• The Nigrosin stain is a form of negative staining. It colors the background, leaving the thick polysaccharide capsule of Cryptococcus unstained, which appears as a distinct, clear halo around the yeast cell.
• This microscopic appearance of a budding yeast with a surrounding halo in the CSF of a patient with meningitis symptoms is the classic diagnostic sign for cryptococcal meningitis.

Why Other Options Were Wrong

• Option A: Aspergillus fumigatus is a mold, not a yeast. It grows as filamentous, septate hyphae and does not form encapsulated budding cells.
• Option B: Pneumocystis jirovecii is a fungus that primarily causes pneumonia (PCP), not meningitis. Its characteristic form seen in lung tissue or bronchoalveolar lavage is a cyst, which appears cup-shaped on silver stain, not an encapsulated yeast.
• Option C: Histoplasma capsulatum is a dimorphic fungus that appears as a small, intracellular yeast in tissue but crucially lacks the large polysaccharide capsule seen in Cryptococcus.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Microscopic identification of fungal pathogens in cerebrospinal fluid (CSF) to guide bedside assessment, documentation, and the next nursing action.
• Rapid identification of Cryptococcus neoformans in CSF is critical for initiating prompt antifungal therapy (e.g., amphotericin B and flucytosine), which can be life-saving, especially in immunocompromised patients such as those with HIV/AIDS.
• The presence of cryptococcal meningitis is an AIDS-defining illness. Nurses should be aware of this association and ensure appropriate infection control and patient support.
• What if? If the stain showed small, oval yeasts inside macrophages without a capsule, the most likely agent would be Histoplasma capsulatum, particularly if the patient had a relevant travel or exposure history (e.g., Ohio/Mississippi River Valleys).

How to Approach the Question

• First, analyze the patient's clinical presentation: fever, headache, and neck stiffness are classic signs of meningitis.
• Next, focus on the key laboratory finding from the CSF analysis: 'encapsulated budding yeast cells' visualized with a Nigrosin stain.
• Recognize that Nigrosin is a negative stain designed to make capsules visible as clear halos against a dark background.
• Systematically evaluate each fungal option based on its known morphology (yeast, mold, hyphae, capsule) and typical disease presentation.
• Correlate the finding of an 'encapsulated budding yeast' with the known characteristics of Cryptococcus neoformans, which is the only option that perfectly matches this description and is a common cause of meningitis.

Concept Tested & Keywords

• Concept Tested: Microscopic identification of fungal pathogens in cerebrospinal fluid (CSF)
• Stem keywords: meningitis, CSF examination, Nigrosin stain, encapsulated budding yeast
• Lead-in keywords: most likely causative agent
• Clinical cues: Patient presents with fever, headache, and neck stiffness, classic signs of meningitis.
• Clinical cues: The key diagnostic finding is 'encapsulated budding yeast cells' in the CSF.

Question ID

Q6r4e7YqbJ8EhWi5zyLVIK

Copy ID

Reference Book

E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 393-395

E6 Nursing Brunner Adult Health 3SA Vol 2 Part 2 p. 124-126

E6 Medicine Davidson Principles Practice 24e p. 322-324