Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A : Many bacteria are inherently insensitive to penicillin-G
Reason R : In such bacteria, the target enzymes and PBPs are located deeper under lipoprotein barrier where penicillin-G is unable to penetrate or have low affinity for penicillin-G
In light of the above statements, choose the correct answer from the options given below:

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

To remember this concept: Gram-positive bacteria lack an outer membrane, making them highly susceptible to Penicillin-G. Gram-negative bacteria possess a protective outer lipid membrane barrier, making them naturally resistant.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bacterial resistance to antibiotics can be inherent (natural) or acquired.
Inherent resistance is due to the natural structural and physiological characteristics of the bacterial cell, which prevent the antibiotic from reaching or binding to its target site.
Penicillin-G is a natural, hydrophilic $\beta$-lactam antibiotic that targets penicillin-binding proteins (PBPs) involved in cell wall synthesis.

Step 2: Detailed Explanation:
Let us analyze the statements:
1. Assertion A: Many bacteria are inherently insensitive to penicillin-G
This statement is correct.
Many bacterial species, particularly Gram-negative bacteria (such as Pseudomonas aeruginosa and Escherichia coli), are naturally insensitive to clinically relevant concentrations of Penicillin-G.
Unlike Gram-positive bacteria, they are not easily inhibited by this natural penicillin.
Therefore, Assertion A is true.
2. Reason R: In such bacteria, the target enzymes and PBPs are located deeper under lipoprotein barrier where penicillin-G is unable to penetrate or have low affinity for penicillin-G
This statement is correct.
Gram-negative bacteria possess a complex outer cell membrane composed of lipopolysaccharides, lipoproteins, and phospholipids.
This outer membrane acts as a highly effective hydrophobic physical barrier.
Because Penicillin-G is a large, hydrophilic molecule, it cannot easily penetrate this outer membrane to reach the peptidoglycan layer and PBPs located in the periplasmic space.
Furthermore, some bacteria possess PBPs that naturally have a low binding affinity for Penicillin-G.
This structural barrier and binding profile explain why these bacteria are inherently insensitive to the drug.
Since this physical barrier directly explains the natural insensitivity, Reason R is the correct explanation of Assertion A.

Step 3: Final Answer:
Both Assertion A and Reason R are true, and Reason R provides the exact physiological explanation for Assertion A.
Therefore, the correct option is (A).