Fleming qualified with distinction from St Mary’s in 1906 with an MBBS degree.
He entered St Mary’s Hospital Medical School in Paddington in 1903, after first working in a London shipping office. His elder brother Tom, already a doctor, encouraged him to pursue medicine. The MBBS—Bachelor of Medicine, Bachelor of Surgery—was his initial medical qualification.
Fleming then joined Sir Almroth Wright’s research department at St Mary’s, helped partly by his success as a rifleman on the medical school’s team. In 1908 he gained a BSc with a gold medal in bacteriology, a separate qualification that is sometimes confused with the 1906 MBBS.
His medical training led into wartime bacteriology, research on antiseptics and, later, the discovery of penicillin. Fleming became a lecturer at St Mary’s and eventually Professor of Bacteriology at the University of London in 1928.