Non-oxidative antibacterial activity of bovine neutrophil granule proteins towards mastitis pathogens

Acid extracts of bovine neutrophil granules displayed potent antibacterial activity towards a number of mastitis pathogens in vitro. Killing of pathogens by acid extractable granule protein was dependent on incubation time, protein concentration, bacterial cell load, pH and ionic strength. Gram-negative and Gram-positive organisms showed variable sensitivity to granule extract. Strains of Staphylococcus aureus were the most resistant of tested organisms to granule extract. Gram-negative organisms were neither consistently more nor less sensitive than Gram-positive organisms. Maximal killing of Gram-positive pathogens, after 30 minutes exposure to granule extract at 37 degrees C, occurred between pH 7.0 and 8.0. The Gram-negative organism Escherichia coli B117 was more sensitive to neutrophil granule extract at pH 5.0.