Cell surface analysis and adhesion of chemically modified streptococci

In this paper, streptococcal cell surfaces are chemically modified, and the effects of the modification on cell surface hydrophobicity and charge, tog ether with adhesion to hexadecane are determined. Acetic and succinic anhyd rides, neutralizing or converting ammonium groups into negatively charged g roups, respectively, had little influence on the water contact angle of the Streptococcus salivarius HB, but acetic anhydride modification reduced the water contact angle of the slightly more hydrophobic Streptococcus oralis 34 from 74 to 58 degrees. This reduction in water contact angle was accompa nied by a more negatively charged cell surface, as inferred from particulat e microelectrophoresis and a decrease in the amount of nitrogen-rich surfac e groups, detected by X-ray photoelectron spectroscopy. Carbodiimide follow ed by ethanolamine or ethylenediamine, compensating negatively charged carb oxylate groups, slightly increased the water contact angles on the hydropho bic S. oralis 34, but strongly increased the water contact angle on S. sali varius HB by 32 degrees on average. Simultaneously, both strains became pos itively charged over the pH range from 2 to 9 and more nitrogen-rich groups were detected on the cell surfaces at the expense of oxygen-rich groups. A dhesion to hexadecane of the streptococcal strains was hardly affected by a nhydride modifications, but both strains adhered better to hexadecane after ethanolamine or ethylenediamine modifications, especially at elevated pH v alues due to electrostatic attraction between the negatively charged hexade cane and the positively charged cell surfaces. This study shows that physic o-chemical cell surface properties of streptococci can be chemically modifi ed to stimulate their adhesion to surfaces. (C) 2001 Academic Press.