Question

Which one of the following is NOT correct about antibiotic resistance mechanism in microbes?

• A. Mycoplasma is naturally resistant to penicillins due to presence of R plasmid.
• B. Gram-negative bacteria are impermeable to penicillin G.
• C. $\beta$-lactamases of bacteria can cleave penicillins.
• D. Selective microbes can efflux penicillins entering the cell and develop resistance.

Hint:

Mycoplasma is resistant to penicillin due to {absence of a cell wall}, not due to R plasmid. Always check the biological basis before assuming plasmid-mediated resistance.

Answer 1

The Correct Option is A

Step 1: Analyze each option.
- (A) Incorrect: Mycoplasma lacks a cell wall, so it is naturally resistant to penicillin. This resistance is due to the absence of peptidoglycan target, not because of R plasmid. Hence this statement is NOT correct.
- (B) Correct: Gram-negative bacteria possess an outer membrane that restricts entry of penicillin G, making them relatively impermeable.
- (C) Correct: Many bacteria secrete $\beta$-lactamases which enzymatically cleave the $\beta$-lactam ring of penicillins, inactivating them.
- (D) Correct: Active efflux pumps can extrude penicillin molecules, contributing to antibiotic resistance.
Therefore, the statement that is NOT correct is (A).