Phagocytosis of serum-resistant and serum-sensitive coliform bacteria (Klebsiella) by bovine neutrophils from blood and mastitic milk.

Phagocytic activity of neutrophil leukocytes from bovine blood and mastitic milk was determined for 2 strains of Klebsiella, 1 resistant and the other sensitive to serum bactericidal activity. Both strains were easily phagocytized in the presence of an opsonic agent, but milk neutrophils seemed to be less efficient than blood neutrophils in this respect. Phagocytosis was maximal after incubation for 60 minutes at 37 C and decreased markedly with reduction in incubation temperature. The opsonic activity of mastitic milk was considerably higher than that of normal milk and approached that of fresh bovine serum. Precolostral calf serum was deficient in opsonic activity and anti-bovine leukocyte serum was antiphagocytic.