A fungal infection of the mitral valve shows silver/Gomori stain positivity. Which organism is most likely to… - INI-CET EXAM -2025

INI-CET EXAM -2025

Applied Microbiology & Infection control

Hard

Appeared in: INI-CET EXAM -2025

Explanation

Aspergillus fumigatus is a common cause of invasive fungal infections, including infective endocarditis, particularly in immunocompromised individuals.
It is a mold known for forming large vegetations on heart valves, which can lead to significant valve damage and systemic emboli.
The Gomori methenamine silver (GMS) stain is a key diagnostic tool in histopathology for identifying Aspergillus.
On GMS staining, Aspergillus exhibits characteristic septate hyphae that branch at acute angles (around 40 degrees), a classic finding that helps differentiate it from other fungi.

Option A: Mucor species cause mucormycosis. While they can cause endocarditis, they are morphologically distinct from Aspergillus. Mucor has broad, non-septate hyphae with wide-angle (often 90-degree) branching.
Option B: Histoplasma capsulatum is a dimorphic fungus that causes histoplasmosis. In tissues, it exists as small, oval yeast cells, often within macrophages. Endocarditis due to Histoplasma is very rare compared to Aspergillus or Candida.
Option D: Candida albicans is the single most common cause of fungal endocarditis. It appears as budding yeasts and pseudohyphae. While it stains with GMS, the question implicitly points to the classic morphology of a mold like Aspergillus, which is a very common cause after Candida.

Visual 1: Micrograph - A Gomori methenamine silver (GMS) stain of tissue infected with Aspergillus fumigatus, clearly showing the black-staining, septate hyphae branching at acute angles.
Visual 2: Diagram - A comparative chart illustrating the microscopic morphologies of Aspergillus, Mucor, and Candida as they would appear on a GMS stain, highlighting the differences in septation and branching angles.

Clinical Relevance

Nursing practice connection: Knowing Identification of the causative agent of fungal endocarditis based on histopathological staining characteristics helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Fungal endocarditis has a very high mortality rate (often greater than 50%) even with treatment, making rapid diagnosis and aggressive management crucial.
Diagnosis often requires a high index of suspicion, especially in at-risk patients (immunocompromised, prosthetic valves, IV drug users), and is confirmed by blood cultures (which can be negative) and echocardiography.
Treatment almost always involves a combination of prolonged systemic antifungal therapy and surgical intervention to remove the infected valve and vegetation.

How to Approach the Question

First, identify the core clinical scenario: a fungal infection of a heart valve (endocarditis).
Next, note the key diagnostic clue provided: positivity with 'silver/Gomori stain'. Recognize this as a special stain for fungi.
Recall or deduce that while GMS stains most fungi, the specific microscopic morphology it reveals is used for differentiation.
Evaluate the options based on their likelihood of causing endocarditis and their classic appearance on stain. Aspergillus is a major cause and has a textbook appearance (acute-angle branching septate hyphae) on GMS stain.
Compare this with the morphology of the other options: Mucor (wide-angle, non-septate), Histoplasma (intracellular yeast), and Candida (yeast and pseudohyphae).
Conclude that the description best fits the classic histopathological presentation of invasive aspergillosis.

Concept Tested & Keywords

Concept Tested: Identification of the causative agent of fungal endocarditis based on histopathological staining characteristics.
Stem keywords: fungal infection, mitral valve, silver/Gomori stain
Lead-in keywords: most likely

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