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.