Is Saliva-Induced Aggregation Of Amylase-Binding Oral Bacteria Modulated By α-Amylase? J.E. Bergmann* And H.-J. Gülzow (Department of Preventive Dentistry, Dental School, University of Hamburg) The binding of salivary α-amylase to certain oral viridans streptococci has been implicated as a nutritional advantage for the bacteria, and in the cariogenicity of starch, and to some extend in the adhesion to hydroxyapatite, but not in the aggregation of bacteria. The aim of this study was to detect a possible inhibitory effect, e.g. by competitive binding to an aggregation-relevant bacterial protein or through sterical hindrance, by salivary amylase of saliva-induced aggregation of selected bacteria which bind the enzyme.   Cleared human whole saliva (HWS) was depleted of its α-amylase (HWS-α-d) by immuno-affinity chromatography on immobilized anti--amylase antibody. HWS-α-d, and mixtures of HWS-α-d with various amounts of purified salivary -amylase, were used in aggregation incubations with Strep. mitis SK138, Strep. gordonii SK186, and mixtures of these two strains which both bind salivary α-amylase. Aggregation was monitored by eye and photometrically.   Saliva-induced aggregation was stronger and faster for Strep. mitis SK138 than for Strep. gordonii SK186. Amylase had no detectable effect on the aggregation process either in incubations with one of the strains or in incubations with a mixture of both. This indicated that amylase-binding and aggregation involved different bacterial binding sites which do not sterically hinder each other and which are most probably located on two different molecules.   In conclusion, these bacteria, by binding salivary amylase, cannot escape aggregation and therefore do not seem to gain a survival advantage with regards to clearance from the mouth.