A CRITICAL-APPRAISAL OF POSITIVE COOPERATIVITY IN ORAL STREPTOCOCCAL ADHESION - SCATCHARD ANALYSES OF ADHESION DATA VERSUS ANALYSES OF THE SPATIAL ARRANGEMENT OF ADHERING BACTERIA

Positive cooperativity is a mechanism proposed to account for the adhe sion of bacteria to surfaces. In this paper, two methods that both cla im to assess experimentally cooperative phenomena, viz. Scatchard anal ysis of adhesion data (using adhesion to vials) and analysis of the sp atial arrangement of adhering cells (using a flow chamber), were compa red and critically evaluated. Three oral strains were used and the sub strata involved were glass (hydrophilic) and silicone-coated glass (hy drophobic) employed with or without a salivary coating. Scatchard anal ysis and near-neighbour analysis of adhering cells yield similar concl usions with regard to the mechanism of adhesion of the cells, provided that adhering cells are sufficiently immobilized under the experiment al conditions. In the case of incomplete immobilization, near-neighbou r collection results from sliding of adhering cells rather than from c ooperative phenomena. Also, the agreement between the conclusions from both methods seems to be better, the more reversibly the cells adhere . Positive cooperativity can be absent or present on saliva-coated sub strata with a distinct effect of the substratum hydrophobicity, despit e the presence of an adsorbed film. This suggests that a different pel licle develops on a hydrophobic substratum than on a hydrophilic subst ratum. This is confirmed by our observation that the amino acid compos ition of salivary films is different on both types of substratum.