Question

Read the following statements on Gram staining:
A. Gram negative cells retain primary stain crystal violet because of thick peptidoglycan layer.
B. Iodine is used as mordant in Gram stain to retain CV-I complexes formed.
C. Safranin is the counter stain used.
D. Gram negative cells allow crystal violet stain to wash out, on addition of ethanol due to thin peptidoglycan layer.
E. Crystal violet is the counter stain used whereas safranin is the primary stain used in Gram staining.
Choose the correct answer from the options given below:

• A. A, B, C and E only
• B. C, D and E only
• C. B, C and D only
• D. A, B and C only

Hint:

Remember: Gram positive = purple (crystal violet), Gram negative = pink/red (safranin).

Answer 1

The Correct Option is C

Step 1: Recall principle of Gram staining.
Gram staining differentiates bacteria into Gram positive and Gram negative based on cell wall structure.
- Gram positive: Thick peptidoglycan → retains crystal violet.
- Gram negative: Thin peptidoglycan + lipid → loses crystal violet when ethanol is applied, takes counterstain.
Step 2: Evaluate statements.
- (A) Incorrect: It is Gram positive, not Gram negative, that retains crystal violet due to thick peptidoglycan.
- (B) Correct: Iodine acts as a mordant, forming CV-I complexes.
- (C) Correct: Safranin is the counterstain.
- (D) Correct: Gram negative bacteria lose crystal violet after alcohol treatment.
- (E) Incorrect: Primary stain is crystal violet, counterstain is safranin.
Step 3: Correct grouping.
B, C, D are correct statements.
Step 4: Conclusion.
The correct answer is (C) B, C and D only.