Describe three common mechanisms by which bacteria acquire antibiotic resistance.

• A. Enzymatic inactivation, target modification, efflux pumps, and reduced permeability.
• B. Random mutation that increases susceptibility.
• C. Increased nutrient uptake to dilute drug.
• D. Overproduction of antibiotic.

Answer: (A)

Bacteria resist antibiotics by four broad strategies that keep the drug from doing its job. Enzymatic inactivation means the bacterium makes enzymes that chemically alter or destroy the antibiotic, such as beta-lactamases breaking open the beta-lactam ring. Target modification changes the drug’s binding site so the drug can no longer interact effectively with its target, for example altering penicillin‑binding proteins or methylating ribosomal RNA to prevent drug binding. Efflux pumps actively remove the antibiotic from the cell, lowering the amount that reaches the target. Reduced permeability reduces the drug’s ability to enter the cell, often through changes or loss of porin channels that would normally allow entry.

These mechanisms explain why antibiotics fail: they either neutralize the drug, prevent it from binding, keep it out of the cell, or push it back out once it enters. The listed options reflect these key categories, covering enzymatic inactivation, target modification, efflux, and decreased permeability as common routes to resistance.