To determine if SsTroA is expressed in S. suis 2, total cellular proteins from S. suis 2 cells, purified SsTroA, and negative control protein (Ss1661 protein from S. suis 2) were separated by SDS-PAGE, transferred to a nitrocellulose membrane (GE Healthcare), and probed with anti-SsTroA serum. A 34-kDa protein band was detected in the S. suis 2 cell lysate (Fig. S1B) , indicated that SsTroA is expressed in the bacteria.