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Deposition of the oral bacterium Streptococcus sobrinus HG977 onto glass (water contact angle 0 degrees) and onto FEP-Teflon (fluoroethylenepropylene; water contact angle 110 degrees)was studied in a parallel-plate flow chamber in the presence and absence of polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) adsorbed onto the cells. The zeta potentials of the bacteria ranged from -7.1 to -8.5 mV at pH 6.8 and were not affected by the presence of pAb or mAbs. Hydrophobicity (by water contact angles) increased from 30 degrees (no antibodies) to 88 degrees in the presence of pAb adsorbed onto the bacterial cell surface. The untreated S. sobrinus had a greater tendency to adhere to glass (44.5 x 10(6) cm(-2)) than to FEP-Teflon (18.3 x 10(6) cm(-2)), in accordance with thermodynamic modelling. After preincubation of S. sobrinus with pAb, its clear preference for adhesion to glass disappeared as expected from its increased hydrophobicity. Although for S. sobrinus preincubated with OMVU10 no difference was found in hydrophobicity in comparison to the untreated bacteria, the number of bacteria adhering to glass decreased to 10.2 x 10(6) cm(-2) Formation of bacterial aggregates was found when S. sobrinus, preincubated with pAb or OMVU10, adhered to glass and FEP. This was also observed when untreated bacteria adhered to glass coated with OMVU10, or to FEP coated with OMVU10 or pAb. Adhesion in these experiments is therefore thought to occur via near-neighbour collection induced by the presence of pAb or mAbs. Low numbers of bacteria were removed from glass after draining the flow cell, whereas high numbers of untreated bacteria and bacteria preincubated with OMVU10 were removed from FEP. S. sobrinus cells preincubated with pAb were not removed but piled up. It was concluded that the adhesion of untreated S. sobrinus and S. sobrinus preincubated with pAb is in accordance with thermodynamic modelling, based on the overall wettability of the cell surfaces, whereas the adhesion of S. sobrinus preincubated with OMVU10 may be through localized interactions, not expressed in overall surface properties.