The present invention relates to a composition comprising obligate lytic bacteriophages generated by a method comprising subjecting normally in vivo lysogenic, pseudolysogenic or temperate bacteriophages to genetic modifications in vitro, which alters the biological activity of one or more of the individual gene products for establishing, maintaining, controlling or regulating the lysogenic life cycle of the bacteriophages, thereby converting them to obligate lytic bacteriophages, wherein the genetic modification includes modification of a single gene in the operon containing a gene resulting in a gene product for establishing, maintaining, controlling or regulating the lysogenic life cycle of the bacteriophages.
