Frederick William Twort (1877-1950) is an English bacteriologist and person who discovered the original Bacteriophage (the virus that infects bacteria). He worked at St Thomas Hospital in London and was the manager of the Brown Institute for Animals, a pathology research center. Twort was a professor of bacteriology at the University of London. He conducted research on paratuberculosis and discovered that vitamin K is needed for the growth of leprosy bacteria.