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 .