Bacterial Resistance via Impaired Antibiotic Entry

Steps:

• Tetracycline inhibits protein synthesis by binding the 30S ribosomal subunit inside bacterial cells.
• Mutations can confer resistance by altering drug uptake, target binding, or efflux.
• Resistance requires blocking the antibiotic's access to its intracellular target (ribosomes).
• Evaluate choices: only impaired entry prevents the drug from reaching ribosomes.

Why B is correct:

• Tetracycline acts intracellularly on ribosomes; preventing entry blocks access to the target site, per antibiotic pharmacodynamics.

Why the others are wrong:

• A: Tetracycline targets ribosomes, not the cell wall, so binding there is irrelevant.
• C: Tetracycline inhibits translation (protein synthesis), not transcription (RNA synthesis).
• D: Ribosomes synthesize proteins, not antibiotics like tetracycline; this misrepresents the mechanism.

Final answer: B