Detection by physico-chemical techniques of an amphiphilic surface component on Streptococcus mitis strains involved...

Indications for the presence of an amphiphilic molecule in Streptococcus mitis strains cultured on TY-agar were obtained from infrared absorption spectra, especially from the shape of the CH2/CH3 absorption bands around 2900 cm-1, which were absent when strains were grown on blood agar. It was the aim of this study to determine for S. mitis strains grown on different growth media whether the amphiphile is located intracellularly or on the cell surface by measuring zeta potentials, elemental surface compositions and adhesion to hexadecane of differently grown cells. There was no significant effect of the presence of the amphiphile on the zeta potentials of the S. mitis strains, but adhesion to hexadecane was increased by the presence of the amphiphile when the pH of the suspension was such that electrostatic interactions between the organisms and the hexadecane could be neglected. Furthermore, lower N/C surface concentration ratios were found for organisms possessing the amphiphilic molecule. Consequently, it was concluded that the amphiphilic molecule is located on the cell surface, and that it is involved in the non-electrostatic binding of S. mitis cells to surfaces.