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Why did bacteria fail to grow near the Penicillium mold on Fleming's culture plate?
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In 1928, Alexander Fleming observed that Staphylococcus aureus bacteria failed to grow near the Penicillium notatum mold on his culture plate because the mold produced an antibiotic substance known as penicillin.12
This substance prevents bacterial growth by inhibiting the enzymes responsible for cell wall synthesis in replicating microorganisms. Additionally, penicillin activates other enzymes that break down the protective cell wall of the bacteria. Because human cells lack these cell walls, they are not harmed by this process, making penicillin a selectively toxic and effective treatment for various bacterial infections.2