Abstract/Summary

Milk from dairy cows never known to have had an intramammary infection with Streptococcus uberis can inhibit growth of Str. uberis for up to 7 h. This inhibition is abolished if milk is heated to 80 degrees C. Inhibition appears not to be related to immune defences as it occurs in skimmed milk (cell free), is unrelated to the concentration of immunoglobulin and survives heating to 56 degrees C. The effect is partly overcome by addition of selected amino acids and vitamins. It is suggested that the inhibition is caused by a restriction in the supply of essential nutrients part of which may require the conversion of plasminogen to plasmin.