What is the primary mechanism of penicillin resistance in some microorganisms?

• A. Alteration of cell membrane transport mechanisms
• B. Enzymatic methylation of ribosomal RNA
• C. Production of beta-lactamase
• D. Efflux pumps

Answer: (C)

Penicillin resistance most often comes from bacteria producing beta-lactamase enzymes that rapidly hydrolyze the beta-lactam ring of penicillin, inactivating the drug before it can reach its target. With the beta-lactam ring destroyed, penicillin can no longer bind to penicillin-binding proteins to block cell wall synthesis, so the bacterium continues to grow. This enzymatic inactivation is a common and powerful mechanism, often carried on resistance genes that can spread between bacteria, which is why beta-lactamase inhibitors are used in combination therapies to restore activity in some strains. While other resistance strategies exist—such as changes in penicillin-binding proteins or reduced drug entry—the ability to enzymatically destroy penicillin is the primary driver of resistance in many microorganisms.