How were antibiotics discovered?

It is unlikely that anyone alive today can remember what life was like before antibiotics. It was a pivotal point in the history of medicine and probably the whole of mankind. If it weren't for the ingenious speculation of men like Alexander Fleming that not all bacteria live in harmony with other bacteria, we may never have discovered penicillin, the first antibiotic to treat bacterial disease in humans. The Penicillium fungus, a type of mold often seen growing on bread, exudes a chemical that causes the cell wall of certain bacteria to rupture and die. Since then, researchers have studied the various ways bacteria are antagonized to develop new antibiotics.