(A) Scanning electron microscopy pictures of cells adhering to Thermanox. The cells of the femAB null mutant AS145 are highly enlarged, while the femAB+ backcross BB1305 and the wild type BB903 show cells of the same size and appearance. The white bar corresponds to 1 μm. (B) Muropeptide pattern. The corresponding cell walls were digested with muramidase and subjected to reversed-phase HPLC. Major muropeptide components are numbered according to de Jonge . Strains BB903 and BB1305 show a muropeptide profile characteristic of wild type S. aureus strains, with the highest peak in the dimeric fraction (peaks 11 and 12) and a high degree of crosslinking (peaks 15 and higher), while AS145 has the highest peak in the monomeric fraction (peaks 1 to 5) and a reduced amount of oligomeric muropeptides .