Correct Option: D

Sulfonamides were the first drugs acting selectively on bacteria which could be used systemically. Today they are infrequently used, in part due to widespread resistance. The target of sulfonamides, and the basis for their selectivity, is the enzyme dihydropteroate synthase (DHPS) in the folic acid pathway. Quinolones are molecules structurally derived from the heterocyclic aromatic compound quinoline, the name of which originated from the oily substance obtained after the alkaline distillation of quinine. They have antimicrobial activity because of their action against the topoisomerase enzyme. Erythromycin is a macrolide antibiotic used to treat bacterial infections. By binding to the 50s subunit of the bacterial 70s rRNA complex, protein synthesis and subsequent structure and function processes critical for life or replication are inhibited. They prevent peptidoglycan synthesis. Cephalosporins are medicines that kill bacteria or prevent their growth. Cephalosporins disrupt the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity. The final transpeptidation step in the synthesis of the peptidoglycan is facilitated by transpeptidases known as penicillin-binding proteins (PBPs). PBPs bind to the D-Ala-D-Ala at the end of muropeptides (peptidoglycan precursors) to crosslink the peptidoglycan. Beta-lactam antibiotics mimic the D-Ala-D-Ala site, thereby competitively inhibiting PBP crosslinking of peptidoglycan.