Figure 1.

Streptococcus suis epidemic strain 05ZYH33 is more virulent than the non-epidemic strain 1940. (A) CD1 female mice were intraperitoneally injected with 10⁸ CFUs of living S. suis 05ZYH33 and 1940 in 0.1 ml sterile saline. The mortality of mice was recorded at 4-h intervals for 32 h. Cumulative results from three independent experiments, each with 10 animals per group, are shown. (B) Bacteria in the blood (n=5, per group) were counted at 5 h post-infection. (C) The necrosis of PMNs in mice infected by different bacterial strains was assayed using fluorescein isothiocyanate (FITC)-conjugated anti-mouse anti-Ly-6G and propidium iodide (PI) staining. Data represent the values obtained in four independent experiments. THB, Todd-Hewitt broth. (D) S. suis 05ZYH33 or 1940 (10⁸ CFUs) were incubated with human umbilical vein endothelial cells (MOI =100) for 4 h. Cytotoxicity was determined by the lactate dehydrogenase release assay. The data represent the mean ± standard deviation from three independent experiments. (E) Pre-opsonised S. suis 05ZYH33 or 1940 (10⁷ CFUs) were incubated with purified human polymorphonuclear neutrophils (MOI =1) in the presence or absence of recombinant sly protein for 15 min. The number of bacteria phagocytized by the PMNs was counted.