After teaching a group of nursing students about the action of penicillins, the instructor determines that the teaching was effective when the students identify natural penicillins as exerting which type of effect on microorganisms?

I believe the answer is Bactericidal.

Bactericidal refers to the type of substance that kills bacteria. (penicillin is effective to kill staphylococci, streptococci, and meningococci)

Because of this characteristic, natural penicillin is widely used in clinical practices as antibiotics.