Abstract: A lytic virus specific for a target strain of a microorganism and substantially free of undesirable genes may be utilized in processes including control of populations of microorganisms. The virus may include a host-range mutant, or “h-mutant.” A method for generating virus includes growing virus-resistant variants of a target strain of a microorganism in the presence of viruses that are specific for the target strain. Only h-mutant viruses will proliferate. Wild-type virus-resistant and virus-resistant variants of a microorganism are also disclosed, as are methods generating such variants. Methods for controlling target strain microorganisms include introducing virus into a treatment site where control of a population of a target strain microorganism is desired or introducing virus-resistant variants of a microorganism into treatment sites where the presence of the microorganism is desired.

Abstract: Methods for disinfecting external layers from animals include applying phage to the external layers. Phage may be applied before an external layer is removed from a remainder of an animal's body, during the removal process, or following removal of the external layer from the remainder of the animal's body.