Which of the following is a mechanism by which bacteria can resist antibiotics?

• A. Pumping the antibiotic out of the cell
• B. Modifying the target so that it no longer binds the antibiotic
• C. Destroying the antibiotic before it gets into the cell
• D. Adding modifying groups that inactivate the antibiotic

Answer: (B)

Changing the drug’s target so the antibiotic can’t bind is a direct and effective way bacteria resist treatment. When a target like an enzyme or the ribosome is altered—by mutations or chemical modifications—the drug’s binding site changes shape or charge, reducing or eliminating binding. That means the antibiotic can no longer inhibit the target, so the bacteria can keep functioning even in the drug’s presence. This mechanism is broadly applicable because many antibiotics act by binding a specific site, so altering that site can confer resistance across multiple drugs that share the same target.

The other strategies shown—pumping the drug out of the cell, destroying the drug, or adding groups that chemically modify and inactivate the drug—also confer resistance, but they act on the drug itself or its intracellular concentration rather than at the target. Target modification directly blocks the drug’s action at its site, which is why it’s a fundamental and widely encountered resistance mechanism.