In the mid-20th century "microbiology" emerged as a discipline that linked bacteriology with the newer sciences of virology, immunology and infectious diseases. At Penn's School of Medicine, the Bacteriology Department officially changed its name in 1959 to the Department of Microbiology. At HUP, clinical microbiology continued to evolve within the William Pepper Laboratory, although important technological advances impacting the ability to diagnose infections rapidly would not develop until the late 20th century. Antibiotic resistance and nosocomial infections became important issues in the care of hospitalized patients. The recognition of emerging infectious diseases centered on Philadelphia in 1976 with the outbreak of Legionnaires' disease at the Bellevue Stratford Hotel. In addition to a resurgence of sexually transmitted diseases, other new diseases were identified during this period including toxic shock syndrome, Ebola hemorrhagic fever and Lyme disease. Years of applied research in the Pepper Laboratory, closely related to work in Penn's Department of Microbiology, led to several noteworthy developments.

Mid 20th-century microbiologists at Penn