Abstract: The invention includes antibiotic pharmaceutical compositions comprising eukaryotic histone H1 protein and methods of using eukaryotic histone H1 protein to kill or to inhibit the growth of microorganisms, including, but not limited to, human pathogenic bacteria. The invention further includes a eukaryotic histone H1-containing animal feed and methods of improving growth of an animal by supplying the feed to the animal. The invention still further includes a kit comprising a eukaryotic histone H1-containing antibiotic pharmaceutical composition and an instructional material which describes the use of the composition. In addition, the invention includes a vaccine comprising a eukaryotic histone H1 protein and a method of vaccinating an animal using the vaccine.