Match the following choices to the culture descriptions in questions 3 through 6:
a. Chlamydia
b. Coccidioides
c. Histoplasma
d. Mycobacterium
e. Mycoplasma
Microscopic examination of a lung biopsy shows ovoid cells in alveolar macrophages. You suspect these are the cause of the patient’s signs and symptoms, but your culture grows a filamentous organism.

검증된 단계별 안내

Step 1: Identify the key observations from the problem: microscopic examination shows ovoid cells inside alveolar macrophages, and the culture grows a filamentous organism.

Step 2: Recall that ovoid cells inside alveolar macrophages are characteristic of Histoplasma capsulatum, a dimorphic fungus that appears as small yeast cells (ovoid) within macrophages in tissue.

Step 3: Understand that Histoplasma grows as a filamentous mold (mycelial form) in culture at environmental temperatures, which explains the filamentous organism observed in culture.

Step 4: Compare the other options: Chlamydia is an obligate intracellular bacterium, Coccidioides forms spherules in tissue, Mycobacterium is an acid-fast bacterium, and Mycoplasma lacks a cell wall and does not form filaments or ovoid cells in macrophages.

Step 5: Conclude that the description matches Histoplasma (option c) because of the ovoid yeast cells in macrophages and filamentous growth in culture.

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주요 개념

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Intracellular Pathogens and Their Morphology

Some pathogens, like Histoplasma, exist as ovoid yeast cells inside alveolar macrophages, indicating an intracellular lifestyle. Recognizing the typical microscopic appearance of these organisms helps differentiate them from others and guides diagnosis.

Dimorphic Fungi and Filamentous Growth

Dimorphic fungi, such as Histoplasma and Coccidioides, can grow as yeast in tissue and as filamentous molds in culture. This morphological switch is key for identification, as the filamentous form often appears in laboratory cultures despite yeast forms in the host.

Correlation Between Microscopic Findings and Culture Results

Discrepancies between microscopic examination and culture morphology require understanding that some pathogens change form depending on environment. For example, seeing ovoid cells in tissue but filamentous growth in culture suggests a dimorphic fungus rather than bacteria or other microbes.