How does penicillin work and who discovered it?

• A. Inhibits bacterial cell wall synthesis; discovered by Alexander Fleming
• B. Inhibits bacterial protein synthesis; discovered by Alexander Fleming
• C. Inhibits viral replication; discovered by Alexander Fleming
• D. Degrades bacterial DNA; discovered by Alexander Fleming

Answer: (A)

Penicillin works by inhibiting the enzymes that cross-link the bacterial cell wall, specifically the transpeptidases (PBPs) that build peptidoglycan. Without a proper cell wall, growing bacteria burst under osmotic pressure, so this drug is bactericidal. This mechanism is distinct from agents that stop protein synthesis, degrade DNA, or act on viruses. The discovery came from Alexander Fleming, who noticed a mold contamination on a Staphylococcus plate that inhibited bacterial growth and identified the substance as penicillin. While Fleming first demonstrated its antimicrobial effect, later work purified and developed penicillin into a usable antibiotic, but Fleming is credited with the initial discovery.