Antimicrobial activity of bovine psoriasin

Human psoriasin (S100A7) has originally been described as a member of the family of S100 calcium-binding proteins which is overexpressed in patients suffering from psoriasis. The bovine homolog was first identified as a cow-derived respiratory allergen. As Escherichia coli mastitis is a common problem in dairy cattle, and human psoriasin was found to exhibit antimicrobial activity preferentially against E. coli, we examined whether the bovine mRNA is expressed in the mammary gland. To demonstrate the antimicrobial activity of bovine psoriasin, we isolated cDNA from the udder, cloned the bovine psoriasin gene in a bacterial expression vector, and the recombinant protein was expressed in BL21 cells. The in vitro antibacterial activity was tested by performing microdilution susceptibility tests and radial diffusion assays with eight different bacterial strains, thereof three different E. coli strains, and one yeast. The antimicrobial activity of the recombinant bovine psoriasin is comparable with human psoriasin and also limited to E. coli. Psoriasin appears to be a part of the local host defense mechanism in the udder, is a putative candidate for a cow-specific factor influencing mastitis susceptibility, and a possible alternative to conventional antibiotics.