IN-VITRO PHAGOCYTOSIS AND SURVIVAL OF STREPTOCOCCUS-SUIS CAPSULAR TYPE-2 INSIDE MURINE MACROPHAGES

In this study, data on phagocytosis of Streptococcus suis and its surv ival inside macrophages are presented. Mouse peritoneal macrophages we re incubated in the presence of one of five different strains of S. su is capsular type 2: a virulent wild-type strain (1591), a non-capsulat ed non-virulent mutant strain (MZ), a poorly capsulated non-virulent m utant strain (M42), a non-virulent capsulated strain (1330), and the w ild-type reference (virulent) strain S735. Opsonized or non-opsonized bacteria were incubated with macrophages in vitro and samples were obt ained after 1 and 3 h incubation. Phagocytosis as well as live and dea d intracellular organisms were determined by acridine orange and cryst al violet staining. After 1 h incubation, non-opsonized virulent and n on-virulent capsulated bacteria were poorly phagocytosed (by less than 7% of the macrophages), whereas the non-capsulated non-virulent mutan t strain was highly phagocytosed (by more than 68% of the macrophages) . The M42 mutant strain was more phagocytosed than the capsulated stra ins but less than the non-capsulated M2 mutant strain (35%). In contra st, a higher percentage of live bacteria was observed inside macrophag es for the capsulated strains (1591 and S735) than for the non- or poo rly capsulated mutant strains (M2 and M42). Opsonization of bacteria w ith rabbit serum or heat-inactivated rabbit serum significantly increa sed phagocytosis. For every opsonized strain, after 3 h incubation, th e percentage of live bacteria within macrophages was considerably lowe r than the corresponding non-opsonized strains. In conclusion, the cap sule of S. suis type 2 appears to act as an important anti-phagocytic factor. However, virulent capsulated non-opsonized strains can be phag ocytosed by mouse peritoneal macrophages within which they appear to s urvive for at least 3 h. Serum factors other than complement increase not only phagocytosis but also intracellular killing of S. suis of bot h capsulated and non-capsulated strains.