Described herein are methods of inhibiting the growth of or killing a bacterium in an animal subject, preventing or delaying onset of an infection with a bacterium in an animal subject, preventing or delaying onset of a pathogen mediated disease or disorder in an animal subject, or reducing bacterial load in an animal subject, comprising administering an effective amount of a derivatized chitosan to the animal. Also described herein are preparations comprising a chitosan derivative for administration to an animal.
