any of various antibiotics obtained from Penicillium molds (or produced synthetically) and used in the treatment of various infections and diseases
"The doctor prescribed penicillin to treat my strep throat infection."
Any of a group of narrow-spectrum antibiotics obtained from Penicillium molds or synthesized, that have a beta-lactam structure and are active against gram-positive bacteria and used in the treatment of various infections and diseases.
"After her strep throat diagnosis, the doctor prescribed penicillin to effectively kill the gram-positive bacteria causing the infection."