Updated project metadata. The goal of the present study is to understand mechanisms by which SE can infect the bovine host and persist in the mammary gland. For this purpose we determined the whole genome and four plasmid sequences of the SE strain PM221 originating from spontaneous persistent bovine IMI. We compared the genomic data with those of ATCC12228 and RP62A to screen for conserved and acquired gene pools. To confirm and complement these findings two-dimensional difference gel electrophoresis (2D DIGE) involving each three strains, surfome shaving and experimental infections in a bovine model was applied to indicate potential differences.