Which scientist is credited with discovering penicillin, the first antibiotic?

• A. Louis Pasteur
• B. Robert Koch
• C. Alexander Fleming
• D. Gregor Mendel

Answer: (C)

Penicillin was discovered when Alexander Fleming noticed that a mold contaminant, later identified as Penicillium notatum, inhibited the growth of Staphylococcus on one of his petri dishes. The mold created a clear zone where bacteria didn’t grow, signaling that a substance—penicillin—was killing the bacteria. This observation identified penicillin as the first true antibiotic, capable of treating bacterial infections and transforming medicine. Fleming’s finding laid the groundwork, while Howard Florey and Ernst Boris Chain later purified and developed penicillin into a usable drug for mass production. The other scientists contributed essential ideas in biology—Pasteur advanced germ theory and vaccines, Koch identified disease-causing bacteria and postulates, Mendel established the basics of genetics—but none discovered penicillin. The core takeaway is that Fleming’s observation of the mold’s antibacterial effect led to penicillin, the first antibiotic.