Wide-spectrum antibiotic activity of bovine granulocyte polypeptides

The antibiotic activity of a polypeptide fraction purified from bovine granulocyte granules was tested against Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Bacillus subtilis, Bacillus stearothermophilus, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus faecalis, Streptococcus pyogenes, and clinical isolates of Staphylococcus and Enterobacter spp. All of these bacterial species were susceptible to the antibiotic polypeptide(s), with MICs ranging from 3 to 100 micrograms of protein per ml. The antimicrobial activity was resistant to boiling and abolished by proteinase treatment. Saccharomyces cerevisiae and human fibroblasts grew normally in the presence of 100 and 50 micrograms of antibiotic polypeptide(s) per ml, respectively. [3H]thymidine incorporation into bacterial, but not fibroblast, DNA was efficiently and promptly inhibited by the antimicrobial polypeptide preparation. This suggests that its main target is a component of the system, which catalyzes and regulates the biosynthesis of bacterial DNA.