USC study of fruit flies finds no cause-and-effect link between increased bacterial load and aging Bacteria – you can live without ‘em, but it won’t do you any good, according to a study of fruit flies by University of Southern California biologists. Flies scrubbed clean of bacteria did not outlive their grubby siblings, the researchers report in the August 8 issue of Cell Metabolism. The finding challenges the conventional wisdom that even harmless bacteria – and the immune response they provoke – suck up the energy of the host organism and hasten its death.