SPECIAL STAINS. PART 5 Flashcards
Gomori's Methenamine Silver (GMS)
What does gomori’s methenamine silver stain
Fungi
Mention the forms that fungi represents in tissues
- Hyphae
- Endosporulating spores
- Budding yeasts
How are fungal infections recognized on a tissue
Are diagnosed relatively easily on H&E-stained
sections when their classic features are seen
Why is it not advisable to rely solely on H&E staining for diagnosing fungal infections?
- Some fungi may be easily overlooked in H&E-stained sections, especially if they are not naturally pigmented or present in low numbers.
- Poorly stained fungi can be difficult to differentiate from tissue components.
- Classic features of fungi may be absent or altered due to factors like fungal therapy.
What other organisms are stained with gomori’s methenamine silver
- Pneumocystis spp
- Microsporidian organisms
- Some bacterial organisms(Klebsiella pneumoniae and
Streptococcus pneumoniae) - Microsporidian organisms
Explain the principle of gomori methenamine silver
The initial step of the GMS stain is similar to that of the Periodic acid-Schiff stain (PAS, covered later in the book) in that it uses chromic acid as an oxidizing agent.
During this step, chromic acid oxidation forms aldehydes from fungal cell wall mucopolysaccharide components.
The tissue is then treated with methenamine silver nitrate solution. During this step, the aldehyde groups react with the silver nitrate, reducing it to metallic silver, which appears black.
periodic acid and will oxidize some of the aldehyde groups further. This produces a substance that cannot react with silver ions. The collagenous background in tissues,
therefore, does not stain. When a counterstain of light green solution is used, the fungal elements stain black with sharp margins and a cleared center against a light green tissue background
What does the presence of fungi in tissues indicate
Invasive infection
