13. The Discovery of Penicillin (1928)
In 1928, Scottish bacteriologist Alexander Fleming returned from vacation to find a Petri dish of Staphylococcus bacteria contaminated with mold. Observing that bacteria surrounding the mold were destroyed, he identified the mold as *Penicillium* and named the antibacterial substance it produced “penicillin.” This serendipitous discovery revolutionized medicine, leading to the development of antibiotics that have saved countless lives (pmc.ncbi.nlm.nih.gov).
