Final answer:
Antimicrobial drugs often target the unique cell wall components like chitin and peptidoglycan in fungal and bacterial cells, as well as ergosterols in fungal cell membranes, which are not found in human cells.
Step-by-step explanation:
An essential cellular feature targeted by antimicrobial drugs, which is found in both bacteria and fungi but not in human cells, is the presence of different cell wall components and membrane sterols. In fungi, the cell walls contain chitin, while bacterial cell walls have peptidoglycan. Human cells lack cell walls, and the sterols in their membranes are different from those in fungi.
Thus, antimicrobial drugs often target the synthesis of chitin or peptidoglycan, as well as the sterols in fungal membranes, namely ergosterols, without harming human cells due to these distinct structural differences. Fungi, on the other hand, have cell walls made of chitin, and this difference can be exploited as a target for antifungal drugs. Human cells do not have cell walls, making them unaffected by these drugs.