EFFECT OF POLYCLONAL AND MONOCLONAL-ANTIBODIES ON SURFACE-PROPERTIES OF STREPTOCOCCUS-SOBRINUS

In this study, the effect of antibody adsorption on physicochemical pr operties of Streptococcus sobrinus was studied. Bacteria were preincub ated with polyclonal antibodies or with OMVU10, a monoclonal antibody (MAb) reactive with S. sobrinus. The zeta potentials and the hydrophob icity as determined by microbial adhesion to hydrocarbons were measure d in potassium phosphate buffer with a pH ranging from 2 to 9, S. sobr inus preincubated with polyclonal antibodies was positively charged at pH 2, 3, and 4 and had an isoelectric point at pH 4.8. Untreated S. s obrinus cells or cells preincubated with MAbs were negatively charged over the whole pH range. X-ray photoelectron spectroscopy showed a dec rease in O/C and P/C ratios for bacteria preincubated with polyclonal antibodies. A combination of the pH-dependent zeta potential and the X -ray photoelectron spectroscopy data of the overall chemical compositi on of the cell surface suggests that polyclonal antibody adsorption oc curs through blocking of surface phosphate. The measurement of hydroph obicity by microbial adhesion to hydrocarbons revealed that S. sobrinu s preincubated with polyclonal antibodies was hydrophobic (90% of the bacteria bound to hexadecane), whereas the controls were relatively hy drophilic. S. sobrinus preincubated with OMVU10 was found to be more h ydrophobic than the controls at pH 5 and 7. Hydrophobicity as measured by water contact angles shelved an increase in hydrophohicity when S. sobrinus was preincubated with polyclonal antibodies. The epitopes to which the antibodies are directed were visualized by immunogold label ing and electron microscopy. The results suggested that OMVU10 is reac tive with only a few epitopes of the cell surface, whereas polyclonal antibodies were found to be reactive with many epitopes. In conclusion , adsorption of polyclonal antibodies was found to influence the overa ll physicochemical surface properties of the organism, probably by for ming a coating over the whole cell surface. Adsorption of MAbs was mor e localized, which could explain their lesser influence on these surfa ce properties.