Lysostaphin expression in mammary glands confers protection against staphylococcal infection in transgenic mice

Infection of the mammary gland, in addition to causing animal distress, is a major economic burden of the dairy industry. Staphylococcus aureus is the major contagious mastitis pathogen, accounting for approximately 15-30% of infections, and has proved difficult to control using standard management practices. As a first step toward enhancing mastitis resistance of dairy an imals, we report the generation of transgenic mice that secrete a potent an ti-staphylococcal protein into milk. The protein, lysostaphin, is a peptido glycan hydrolase normally produced by Staphylococcus simulans. When the nat ive form is secreted by transfected eukaryotic cells it becomes glycosylate d and inactive. However, removal of two glycosylation motifs through engine ering asparagine to glutamine codon substitutions enables secretion of Gln( 125,232)-lysostaphin, a bioactive variant. Three lines of transgenic mice, in which the 5'-flanking region of the ovine beta -lactoglobulin gene direc ted the secretion of Gln(125,232)-lysostaphin into milk, exhibit substantia l resistance to an intramammary challenge of 10(4) colony-forming units (c. f.u.) of S. aureus, with the highest expressing line being completely resis tant. Milk protein content and profiles of transgenic and nontransgenic mic e are similar. These results clearly demonstrate the potential of genetic e ngineering to combat the most prevalent disease of dairy cattle.