Figure 6

Oxidative burst of granulocytes (A) and survival factors (B) of S. suis strains in porcine blood. Bactericidal assays were conducted in parallel with oxidative burst experiments in blood of 9-week-old piglets (n = 6). After adding 1 × 10⁶ CFU of S. suis to 300 µL of heparinized blood, the samples were divided into two immediately. For determination of oxidative burst, one sample of each pair was incubated for 20 min at 37 ℃ and for a further 10 min after the addition of DHR 123 (5 μg/mL). As DHR 123 reacts to Rho 123 in the presence of reactive oxygen species, the oxidative burst is shown as a percentage of Rho123 positive granulocytes. Following erythrocyte lysis, the samples were directly measured by flow cytometry (A). SFs (B) were determined in the other sample of each pair after 2 h of infection (150 μL of heparinized blood infected with 5 × 10.⁵ CFU of the indicated S. suis strain). For statistical analysis, Friedman followed by Dunn’s multiple comparisons test was performed both in oxidative burst experiment and bactericidal assays among 9 S. suis strains including 8 wt strains and 1 unencapsulated isogenic mutant 10cpsΔEF. Differences that are not indicated are not significant. Significant differences are indicated (*p < 0.05, **p < 0.01, and ***p < 0.001). Spearman correlations between S. suis induced oxidative burst rates with the respective streptococcal SF (C).