FIGURE 3.

Characterization of S. suis D282-sadP and S. suis D282-srtA knock-out strains. A, the phenotype of the S. suis D282-sadP knock-out strain, after the insertion of the suicide vector into the sadP (supplemental Fig. 3) was confirmed, was tested in a 96-well microtiter plate hemagglutination assay. 5 × 10⁹ cfu/ml of bacteria were 2-fold diluted in microtiter wells and were then mixed with sialidase-treated erythrocytes (2.5% (v/v) final concentration). Wild-type S. suis D282 strain caused a positive reaction up to a concentration of 3 × 10⁸ cfu/ml whereas the D282-sadP knock-out strain was negative even in the lowest dilution. Strain D282-981782 is an insertional knock-out mutant of the 35-kDa pigeon ovomucoid-binding protein (*3 in Fig. 1). Strain D282-Δdpr is a full deletion mutant, and D282-33 is an insertional mutant of S. suis dpr, which encodes for a bacterial ferritin-like protein Dpr required for H₂O₂ resistance of catalase-negative S. suis (30, 36), previously identified as a pigeon ovomucoid-binding protein (35). B, wild-type S. suis D282 strain caused a positive reaction up to a concentration of 3 × 10⁸ cfu/ml whereas the sortase A-negative D282-srtA knock-out strain was negative.