This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Histo Pathology, Subject name: Pathology
The stain used to detect amyloid is? 
Select and explain. 
A. Grams stain, B. Congo red, C. Oil red O, D. Reticulin stain
B: Congo red
Answer: B: Congo red 
Explanation: Ans. (b) Congo redRef: Robbin's pathology 9th ed. 1257* In biochemistry and histology, Congo red is used to stain microscopic preparations especially as a cytoplasm and erythrocyte stain.* Apple-green birefringence of Congo red stained preparations under polarized light is indicative for the presence of amyloid fibrils.* Additionally, Congo Red is used in microbiological epidemiology to rapidly identify the presence of virulent serotype 2A ShigellaFlexneri, where the dye binds the bacterium's unique lipopolysaccharide (LPS) structure