Influence of saliva on aggregation and adherence of Streptococcus gordonii HG 222

The influence of saliva on the aggregation and adherence of Streptococcus gordonii HG 222 was studied. The aggregation was measured spectrophotometrically, and the adherence of S. gordonii to microtiter plate wells was measured in an enzyme-linked immunosorbent assay system. The aggregation of HG 222 was induced primarily by mucous saliva, whereas the adherence of HG 222 to microtiter plates was mediated by both mucous and serous saliva. Fractions of submandibular saliva, obtained by gel filtration and containing low-molecular-weight mucins (MG-2), induced both bacterial aggregation and adherence. Purified MG-2 induced aggregation and promoted adherence, whereas high-molecular-weight mucins (MG-1) did not. After incubating clarified human whole saliva with HG 222, only MG-2, and not MG-1, was bound by the bacteria. Proline-rich proteins (PRPs) and proline-rich glycoprotein (PRG) promoted the adherence of HG 222. These proteins in solution bound to HG 222 but did not induce aggregation of the bacterial cells. PRPs and PRG in solution were not able to inhibit adherence to microtiter plate wells coated with the same components. Purified alpha-amylase hardly promoted adherence to microtiter plates but, in the soluble state, readily bound to HG 222. In conclusion, these results indicate that the aggregation of S. gordonii HG 222 is mediated primarily by MG-2. These mucins also promote adherence. Several other salivary components, such as PRPs and PRG, are also involved in the adherence of HG 222.