Final answer:
Antimicrobials that target the bacterial cell wall have a high therapeutic index because they selectively kill bacterial cells without harming human cells.
Step-by-step explanation:
Antimicrobials that target the bacterial cell wall usually have a very high therapeutic index because they exhibit selective toxicity. Selective toxicity means that these drugs selectively kill or inhibit the growth of bacterial cells while causing minimal or no harm to the host cells. The reason why they have a high therapeutic index is because human cells do not have a cell wall composed of peptidoglycan like bacterial cells do. Therefore, these antimicrobials can specifically target and kill bacterial cells without affecting human cells.