Question

Bacterial flagella are stained by

• A. Crystal violet
• B. Basic dye
• C. Carbol fuchsin
• D. Leifson stain

Answer 1

Answer: (D)

Leifson stain

Bacterial flagella are very thin structures that cannot be seen with light microscope and hence, are coated with mordents (tannic acid and potassium alum), which increase their thickness, followed by their staining with pararosaniline; the method is called as Leifson method. Option D is correct. Crystal violet is used in Gram-staining method to identify the Gram positive and Gram negative bacteria by differential staining of peptidoglycan layer. Option A is incorrect. A positive/basic dye carries positively charged chromophores and stains acidic substances carrying negative charge. Presence of acidic substances in large quantity with negatively charged surfaces on the bacterial cell wall allow their staining with basic dyes like crystal violet, safranine, methylene blue etc. Option B is incorrect. Carbol fuchsin is the component of Ziehl–Neelsen stain and is a mixture of phenol and basic fuchsin. It has affinity for acid fast organisms (Mycobacteria , Nocardia) and is used detection of their presence by staining procedure. Option C is incorrect. Thus, the correct answer is option D.