Question

Peptidoglycan is a complex polymer of sugars and amino acids; the substance from which bacterial cell walls are made. Bacteria are divided into Gram positve and Gram negative on the basis of cell wall of the bacteria and Gram's staining. Choose set of correct statements below with respect to Gram nagative bacteria
(A). Gram negative bacteria contain thick layer of peptidoglycan and therefore they stain pink in colour.
(B). Antibiotic penicillin is less effective on Gram negative bacteria
(C). All the genera of the family Enterobacteriaceae consist of Gram negative bacteria
(D). Gram negative bacteria have less peptidoglycan and therefore they stain pink in colour.
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (B), (C) and (D) only.
• D. (A), (C) and (D) only.

Hint:

Remember:
- Gram-positive \(\rightarrow\) Peptidoglycan Plenty (Thick) \(\rightarrow\) Purple.
- Gram-negative \(\rightarrow\) Peptidoglycan Less (Thin) \(\rightarrow\) Pink.
This basic phonetic association helps avoid confusion during exams.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question focuses on bacteriology, specifically evaluating the structural, clinical, and taxonomic characteristics of Gram-negative bacteria relative to their cell wall composition.

Step 2: Detailed Explanation:
Let us evaluate each of the given statements with respect to Gram-negative bacteria:
- Statement (A): "Gram negative bacteria contain thick layer of peptidoglycan and therefore they stain pink in colour."
This statement is false. Gram-negative bacteria have a very thin layer of peptidoglycan (about \( 2 \text{ to } 7\text{ nm} \) thick, comprising only \( 10% \) of their cell wall), surrounded by an outer lipopolysaccharide membrane.
Gram-positive bacteria are the ones that possess a thick peptidoglycan layer (\( 20 \text{ to } 80\text{ nm} \)).
- Statement (B): "Antibiotic penicillin is less effective on Gram negative bacteria"
This statement is true. Penicillin targets the transpeptidase enzyme involved in cell wall peptidoglycan synthesis.
Because Gram-negative bacteria have an outer lipid membrane that acts as a physical barrier, hydrophobic penicillin G cannot easily access the peptidoglycan layer.
This makes them intrinsically more resistant (less susceptible) to penicillin than Gram-positive bacteria.
- Statement (C): "All the genera of the family Enterobacteriaceae consist of Gram negative bacteria"
This statement is true. The family Enterobacteriaceae (which includes medically important genera like Escherichia, Salmonella, Shigella, and Klebsiella) is a taxonomic group comprised entirely of Gram-negative, rod-shaped bacteria.
- Statement (D): "Gram negative bacteria have less peptidoglycan and therefore they stain pink in colour."
This statement is true. Because Gram-negative bacteria have a thin peptidoglycan layer, the crystal violet-iodine complexes are easily washed out by alcohol during the decolorization step.
Consequently, they take up the safranin counterstain and appear pink under the microscope.
Therefore, statements (B), (C), and (D) are correct, while statement (A) is incorrect.

Step 3: Final Answer:
The correct set of statements is (B), (C), and (D) only.
Therefore, the correct choice is Option (C).