Question

Basic dyes are used in microbiological staining. Which of the following statement is wrong about mechanism of staining?

• A. The positive ions on the surface of bacteria form a coloured complex with the dye
• B. Ionic exchange between the negative charge on the bacteria and positive charge of dye takes place
• C. Ionic exchange between the positive charge on the bacteria and negative charge of dye takes place
• D. The neutral charge on the surface of bacteria forms a coloured complex with the basic dye

Answer 1

The Correct Option is D

To solve the question regarding the mechanism of staining with basic dyes in microbiology, let's explore the basic principles involved in bacterial staining:

1. Understanding Basic Dyes: Basic dyes are cationic, meaning they have a positive charge. Common examples include crystal violet and methylene blue. These dyes are used primarily in staining techniques like Gram staining.
2. Mechanism of Staining: The surface of bacterial cells typically carries a negative charge due to the presence of molecules like peptidoglycans. When using basic dyes, the positively charged dye ions interact with the negatively charged bacterial cells.
3. Option Analysis:
   • The positive ions on the surface of bacteria form a coloured complex with the dye: This statement is incorrect as it contradicts the basic principle of ionic interaction where the bacteria surface is negatively charged.
   • Ionic exchange between the negative charge on the bacteria and positive charge of dye takes place: This is accurate. The positive dye ions are attracted to the negatively charged bacterial surfaces, leading to binding and staining.
   • Ionic exchange between the positive charge on the bacteria and negative charge of dye takes place: This is incorrect because the bacterial surface is negatively charged, not positive.
   • The neutral charge on the surface of bacteria forms a coloured complex with the basic dye: This is incorrect as the bacterial surface is not neutral. The main interaction is between positively charged dyes and negatively charged bacterial surfaces.
4. Conclusion: The incorrect statement is: "The neutral charge on the surface of bacteria forms a coloured complex with the basic dye". This contradicts the known mechanism of interaction between basic dyes and bacterial cells.