In Vitro Bactericidal Reactions of Serums and Milks Obtained from Cows Inoculated with Selected Serum-Resistant and Serum-Sensitive Coliform Bacteria

SUMMARY In vitro bactericidal reactions of serums and milks obtained from cows at various times before and after inoculation of the udder with selected coliform organisms are described. Serum-resistant (sr) organisms generally grew in the preinoculation milks, whereas serum-sensitive (ss) organisms either did not grow or were killed. The sr organisms had previously been demonstrated to be mastitogenic, whereas ss organisms were not. The development of mastitis in inoculated glands presaged the appearance of bactericides in the milk that are always lethal for ss organisms, but usually not for sr organisms. Since both organisms grew in normal milk in vitro, it is maintained that failure of ss organisms to grow and induce mastitis in normal quarters in vivo is due to their sensitivity to the bactericidal system in the milk, and growth and induction of mastitis in normal quarters in vivo by sr organisms is due to their ability to resist killing by this system.