FIG 4.

Characterization of the cellular pathways involved in the internalization process of S. delphini. (A) Role of soluble fibronectin in invasion of S. delphini. The invasion assay was performed in the presence of 10% FBS (control condition), in the presence of 10% fibronectin-depleted FBS, and in the absence of FBS. Invasion is expressed as a percentage of that observed in the presence of 10% FBS. The horizontal bars indicate the mean derived from three independent experiments performed in quadruplicate. Statistical significance was determined by one-way ANOVA followed by Dunnett’s multiple-comparison test using 10% FBS as a control with an α risk of 0.05 (***, P ≤ 0.0001). (B) Evaluation of the involvement of the β₁ integrin in the S. delphini internalization process using murine osteoblast cell lines (OB-β₁^fl/fl and OB-β₁^−/−) with functional and nonfunctional β₁ subunits, respectively. The internalization capacity of S. aureus 8325-4 (positive control), DU5883 S. aureus ΔfnbA/B (negative control), and the reference strain S. delphini DSM 20771^T in OB-β₁^fl/fl and OB-β₁^−/− osteoblasts was measured 3 hours postinfection from three experiments performed in triplicate. The two-tailed Student’s t test was used to compare the data obtained for the OB-β₁^fl/fl and OB-β₁^−/− osteoblasts with an α risk of 0.05 (***, P < 0.0001).