Which of the following is NOT considered a bacteriostatic agent?

Penicillin is primarily classified as a bactericidal agent, meaning it kills bacteria rather than merely inhibiting their growth. Unlike bacteriostatic agents, which slow down bacterial reproduction and rely on the host's immune system to eliminate the pathogens, penicillin works by interfering with the synthesis of the bacterial cell wall. This leads to cell lysis and ultimately the death of the bacteria.

In contrast, tetracyclines, sulfonamides, and macrolides function as bacteriostatic agents. Tetracyclines inhibit protein synthesis by binding to the bacterial ribosome, sulfonamides interfere with folic acid synthesis, and macrolides also inhibit protein synthesis but through a different mechanism. Because these agents rely on inhibiting bacterial growth rather than killing the bacteria outright, they are categorized as bacteriostatic, whereas penicillin’s mechanism of action classifies it as bactericidal.