Cell surface proteins (biofilm matrix and cell wall fractions) isolated from S. aureus MR23 biofilms were separated by one-dimensional (1D) SDS-PAGE. The major protein bands with apparent molecular masses of 60 kDa and 15 kDa were identified by N-terminal amino acid sequence analyses as described previously (20). Topdown proteomic analysis was also performed to identify proteins that are degraded by Esp (details are described in the supplemental material)