Variation in the expression of cell wall proteins of Staphylococcus aureus grown on solid and liquid media

Abstract

To evaluate the variation in the expression of cell wall antigens between Staphylococcus aureus grown in liquid medium and solid support, bacteria were harvested from liquid chemically defined medium and chemically defined medium in a 1% agar base. Cell wall proteins were then extracted by lysostaphin in a protoplast-stabilizing medium (30% raffinose). After separation of the cell wall antigens by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots, they were probed with chicken antiserum to an S. aureus strain grown on a solid support. For each of the 15 clinical strains analyzed, high-molecular-size bands (molecular size range, 120 to 220 kilodaltons) were either enhanced or distinctly present when compared with those from the cell wall extract of the same strain grown in liquid medium. Results of enzymatic treatment of whole staphylococci grown on solid medium suggested the proteinaceous nature and the surface location of these antigens. Limited passage studies demonstrated the ability of the staphylococci to alter these surface proteins when passaged alternately on liquid and solid media. These observations suggested the importance of the microenvironment to the expression of cell wall proteins in S. aureus. Correlations with observations in vivo may help identify the determinants of microbial pathogenicity in S. aureus.