Which of the following is a bactericidal agent?

Penicillin is classified as a bactericidal agent because it works by inhibiting the synthesis of the bacterial cell wall. This disruption ultimately leads to cell lysis and death of the bacteria. Penicillin targets the penicillin-binding proteins (PBPs) that are essential for cell wall construction, making it effective against actively growing bacteria.

In contrast, other options like clindamycin, macrolides, and tetracycline are generally considered bacteriostatic agents. They inhibit bacterial growth and reproduction rather than outright killing the bacteria. Clindamycin and macrolides (such as erythromycin) work by interfering with protein synthesis, while tetracyclines also inhibit protein synthesis by binding to the 30S ribosomal subunit. These mechanisms effectively stop the bacteria from growing but do not necessarily kill them directly, which distinguishes them from bactericidal agents like penicillin.