Several previous studies of phage therapy in animal models of infection found that delaying intervention for more than a few hours after infection mitigated or eliminated entirely any positive treatment effects . In these models, which generally employ a lethality end point, phage intervention must be timed to interrupt the exponential expansion of the infecting bacterial population before the host succumbs. In contrast, in our nonlethal infection model, we found that phages administered well after infection was established were effective in producing positive treatment effects