Read the following passage about the discovery of penicillin.
Fill the gaps in the summary below using words from the passage.
Alexander Fleming discovered penicillin by ______ on September 28, 1928. He found that the growth of bacteria on a petri dish was ______ by a blue-green mould that had contaminated the culture. He realised that the mould was producing a substance that was responsible for ______ bacterial growth.