A new antibiotic irreversibly inhibits transpeptidase enzymes that crosslink peptidoglycan and cannot cross intact lipid membranes efficiently. For which bacteria would you predict the drug to be most effective and why?

• A. Gram-negative bacteria, because their outer membrane provides numerous lipid access routes allowing the drug to reach periplasmic transpeptidases more readily.
• B. Both Gram-positive and Gram-negative equally, because transpeptidases are identical in all bacteria and the membrane permeability does not influence access to periplasmic enzymes.
• C. Neither Gram-positive nor Gram-negative; the drug will only affect intracellular parasites because transpeptidases are located exclusively inside the cytoplasm in all bacteria.
• D. Gram-positive bacteria, because their exposed thick peptidoglycan is accessible without crossing an outer membrane.

Answer: (D)