In vitro incorporation of serine into the staphylococcal cell wall

A variant of Staphylococcus aureus 44A HJD was isolated by serial growth in Trypticase soy broth to which 2 M serine had been added (wt/vol). Amino acid analysis of hydrolysates of purified mucopeptides from the variant showed that they contained 1.266 serine and 2.156 glycine residues per glutamic acid residue, compared with 0.174 serine and 3.144 glycine residues per glutamic acid residue in the mucopeptide of the parent strain. In addition to this alteration in the chemical composition of the mucopeptide, the variant lost many of the biochemical and cultural characteristics of the parent organism. The variant was not sensitive to the lytic action of lysostaphin and was non-phage-typable. Moreover, in vitro tests indicated that the organism was coagulase negative, did not produce gelatinase or deoxyribonuclease, and did not hemolyze sheep erythrocytes. Apparently due to the change in the serine content in the cell wall of the parent S. aureus strain, the organism had become "epidermidis-like" in its properties.