PHAGOCYTOSIS OF STREPTOCOCCUS-UBERIS BY BOVINE MAMMARY MACROPHAGES - OPSONIZING EFFECT OF BOVINE ANTISERUM

Five encapsulated and five non-encapsulated strains of Streptococcus u beris were tested for their ability to resist phagocytosis and intrace llular killing by bovine mammary macrophages obtained during the non-l actating period. The percentage of phagocytosis and intracellular kill ing of encapsulated strains ranged from 43 to 51 and from 25 to 40, re spectively. By contrast, the percentage of phagocytosis and intracellu lar killing of non-encapsulated strains ranged from 66 to 74 and from 65 to 75, respectively. Two encapsulated and two non-encapsulated stra ins were opsonized with homologous and heterologous pre-immune and imm une bovine sera. Phagocytosis and intracellular killing of encapsulate d strains increased significantly when opsonized with serum of cows va ccinated with a homologous and heterologous encapsulated strain. By co ntrast, no significant differences were observed when serum from cows vaccinated with a non-encapsulated strain was used. These results sugg est that resistance to phagocytosis is a common feature among encapsul ated strains of S. uberis, and that cross-reactivity exists between en capsulated strains.