Why Did Alexander Fleming Invent Penicillin?

Alexander Fleming was born in the year 1881 in Lochfield, Scotland. He was of Scottish origin and is known for the discovery of Penicillin. He was a biologist and pharmacologist by origin and got a Nobel Prize in Medicine in the year 1945.

His invention or discovery of Penicillin was just an accident. He was making investigations about properties of staphylococci. He was a good researcher but he could not keep his lab in order. He came back after vacations. He saw many of his dishes were having fungus so he threw them into a disinfectant. 

He observed that some of the dishes were such that they did not get any fungus.  He later identified it from Pencillium Genus so he named it as Penicillin.