An antimicrobial compound that targets a pathway or structure that is present in a pathogen but not in the host exhibits

selective toxicity

Explanation:

Selective toxicity is one of the desired features of a successful chemotherapeutic agent and refers to the ability of the drug to kill or inhibit the pathogen only while not damaging the host organisms or presenting the minimum damage to the host. A drug with selective toxicity normally targets the cellular processes or structures that are pathogen-specific and are not present in the host organisms. For instance, penicillin inhibits the synthesis of peptidoglycan but does not affect the host cell since the animal cells lack cell walls.

a physical change is being made.