Which statement best distinguishes polypeptide antibiotics from beta-lactam antibiotics in structure and primary mechanism of action?

• A. Polypeptide antibiotics are structurally identical to beta-lactams but are modified to be more hydrophobic so they can cross the outer membrane of gram-negative bacteria and inhibit transpeptidation by acting as competitive inhibitors of D-Ala-D-Ala binding at PBPs.
• B. Polypeptide antibiotics are cyclic carbohydrate-based molecules that inhibit the final cleavage of pentaglycine cross-bridges in peptidoglycan, while beta-lactams are protein-based enzymes secreted by microbes that disrupt host cell wall synthesis by binding teichoic acids.
• C. Polypeptide antibiotics are large, lipid-soluble molecules that penetrate bacterial membranes and cleave peptidoglycan backbone directly by chemical hydrolysis of glycan strands, unlike beta-lactams that selectively inhibit RNA synthesis by binding ribosomal subunits and also contain a beta-lactam ring structure which is central to their action.
• D. Polypeptides are peptide-based molecules that disrupt earlier steps of peptidoglycan synthesis (e.g., carrier recycling or D-Ala-D-Ala binding) and lack a beta-lactam ring, whereas beta-lactams are small molecules containing a beta-lactam ring that inhibit transpeptidation by binding PBPs.

Answer: (D)