When you take an aspirin, a decongestant, or a muscle relaxant, the drug you’re taking was probably made by a chemist combining a specific mixture of chemicals. Microscopic Fungi And Bacteria Antibiotics, on the other hand, are chemicals produced by microscopic fungi or bacteria as part of their normal biological processes. Pharmaceutical companies grow the microorganisms, collect the chemicals they produce, and sell the chemicals as antibiotics. To see how antibiotics work in nature, it may help to look at the discovery of the first antibiotic. In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria when one of the bacterial cultures became infected with a fungus called “penicillium.” Penicillium is a fairly common fungus and is one of the fungi responsible for moldy bread. Fleming noticed that the penicillium prevented the Staphylococcus bacteria from growing and reasoned that the fungus must be releasing a chemical that was toxic to the bacteria.