| Streptococcus suis capsular type 2 is an important etiological agent of swine meningitis and it has been highlighted as a cause of occupational disease leading to meningitis and fulminant sepsis in humans. S. suis is a well-encapsulated bacterium and recent studies using isogenic mutants defective in capsule production suggested the antiphagocytic properties of the capsular polysaccharide (CPS). To further elucidate the role of CPS in S. suis interactions with phagocytes and in bacterial mechanisms of dissemination, we evaluated quantitatively the uptake and intracellular survival of S. suis type 2 in murine macrophages. The role of the capsule was also evaluated using a previously obtained unencapsulated isogenic mutant. The encapsulated S. suis wild type strain was practically not phagocytosed, whereas the unencapsulated mutant was easily ingested and killed by macrophages. These results further suggest that S. suis is able to resist uptake by phagocytes, and thus may use other mechanisms for bloodstream dissemination.; One possible mechanism is that bacteria interact with phagocytes and remain extracellularly bound to the cell surface. Indeed, by using an enzyme-linked immunosorbent assay technique, we demonstrated high levels of S. suis adhesion to murine macrophages. Inhibition studies showed that the sialic acid moiety of the S. suis capsule was, at least in part, responsible for bacterial recognition by macrophages. Serum pre-opsonization of bacteria increased adhesion levels, and complement would be partially involved in the serum-enhanced binding of S. suis to cells. High bacterial concentrations of some isolates were cytotoxic for cells, and these cytotoxic effects correlated with production of suilysin, the only cytolysin described to date for S. suis.; To further investigate the consequences of S. suis interactions with phagocytes in the inflammatory reaction, we evaluated the capacity of S. suis to induce the up-regulation pro-inflammatory cytokines tumor necrosis factor alpha (TNF) and interleukin-6 (IL-6) by murine macrophages. Results showed that S. suis stimulated both cytokines in a cytochalasin-insensitive fashion confirming previous results. (Abstract shortened by UMI.)... |
