Who is credited with discovering penicillin?

• A. Alexander Fleming
• B. Louis Pasteur
• C. Robert Koch
• D. Paul Ehrlich

Answer: (A)

The main idea is recognizing the person who first identified penicillin and how that change happened. Alexander Fleming observed that a mold had contaminated one of his petri dishes containing Staphylococcus bacteria, and around the mold there was a clear ring where the bacteria did not grow. He realized the mold released a substance that inhibited bacterial growth, which he named penicillin. This accidental observation led to the first true antibiotic and transformed how infections are treated, saving countless lives and spurring the development of modern antimicrobial therapy.

While Louis Pasteur, Robert Koch, and Paul Ehrlich each made landmark contributions to microbiology and medicine, they did not discover penicillin itself. Pasteur helped establish germ theory and vaccines, Koch identified the bacteria responsible for specific diseases, and Ehrlich pioneered targeted chemotherapy concepts, but Fleming is the one credited with the initial discovery of penicillin.