Felix d'Herelle. Portrait of the French-Canadian bacteriologist Felix d'Herelle (1873-1949). He is generally credited for the discovery of bacteriophages, viruses which infect bacteria, in 1917. D'Herelle isolated the bacteriophage viruses whilst working for the Mexican government at the Louis Pasteur Institute, France. He successfully used the viruses to treat dysentery. Two years earlier a British scientist, F.W. Twort, had discovered bacteriophages, but his work was ignored.