Function of gene 0267 of Streptococcus suis type 2 98HAH33

Abstract

Objective To study the function of gene 0267 of Streptococcus suis type 2 98HAH33. Methods Growth rates of the wild type strain Streptococcus suis type 2 98HAH33, the mutant stain Δ0267 and the complemented strain CΔ0267 at different stages were compared. Bacterial adhesion, whole blood killing and macrophage phagocytosis assays were used to compare the adhesion and anti-phagocytosis of these strains to host cells. A piglet model was used to evaluate their differences in virulence. Results The growth rates of the wild type strain, the mutant strain and the complemented strain were the same. The adhesion rates of the wild type strain and the complemented strain to A549 cells, Hep2 cells and human brain microvascular endothelial cells (HBMEC) were 2.59, 4.87 and 3.08 times, and 2.65, 4.65 and 2.86 times higher than those of the mutant strain, respectively. The survival rates at 1 h, 2 h and 3 h of the wild type strain, the mutant strain and the complemented strain in whole blood were 36.91%, 28.12% and 41.61%, 58.44%, 44.06% and 58.26%, and 93.02%, 70.08% and 95.85%, respectively. Results of the phagocytosis assay showed that the bacterial loads of the wild type strain, the mutant strain and the complemented strain in murine RAW264.7 macrophages were 2 767, 5 322 and 2 567, respectively. The competitive infection experiment using piglets showed that gene 0267 was associated with the virulence of Streptococcus suis type 2 98HAH33. Conclusions Streptococcus suis type 2 98HAH33 gene 0267 is associated with bacterial adhesion and anti-phagocytosis, suggesting that it is a new virulence factor. Key words: Streptococcus suis type 2; Bacterial adhesion; Whole blood killing; Phagocytosis; Virulence factor