Original: His best-known achievements are the discovery of the enzyme lysozyme in 1923 and the antibiotic substance penicillin from the fungus Penicillium notatum in 1928, for which he shared the Nobel Prize in Physiology or Medicine in 1945 with Howard Walter Florey and Ernst Boris Chain.
Simplified: He shared a Nobel Prize in Physiology or Medicine in 1945 for this discovery with Howard Walter Florey and Ernst Boris Chain.