Fleming continued his research at St. Mary's Hospital after the war, focusing on improving methods for penicillin production and exploring the potential of other antibiotics. He also travelled extensively, giving lectures and accepting honorary degrees from universities around the world.

Fleming was appointed Professor of Bacteriology at the University of London. This was a well-deserved recognition of his contributions to the field of bacteriology and his impact on medicine.

Fleming became increasingly concerned about the potential for bacteria to develop resistance to penicillin and other antibiotics. He warned about the dangers of overuse and misuse of these drugs, and he advocated for their responsible use to preserve their effectiveness. His early warnings about antibiotic resistance are now recognized as prescient.

Sir Alexander Fleming died in London at the age of 73 after suffering a heart attack. He was buried in St. Paul's Cathedral.

Fleming's discovery of penicillin revolutionized medicine and saved countless lives. His work laid the foundation for the development of numerous other antibiotics, transforming the treatment of bacterial infections. He is remembered as one of the greatest scientists of the 20th century, and his legacy continues to inspire researchers to develop new ways to combat infectious diseases.