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The mold Penicillium chrysogenum (also known as Penicillium notatum) secretes the antibiotic Penicillin into the space outside its cells. The goal is to kill ordinary bacteria around the mold, because they compete with the mold for food and water. This can be seen as a clear space when Penicillium is grown in a culture dish. This was first noticed by Alexander Fleming in 1928. To read about the story in detail, go to http://botit.botany.wisc.edu/toms_fungi/nov2003.html. The antibiotic was named because it came from the mold Penicillium. Structurally they are completely different.
If you have questions about Pencillin or Penicillium allergies, ask your doctor.