Urea in the oral cavity is hydrolyzed mainly by bacterial ureases to ammonia, which in turn, raises pH of the oral environment, maintaining oral pH homeostasis, thereby inhibiting dental caries. Streptococcus salivarius has been shown to be a major contribution to oral ureolysis. Synthesis of urease by S. salivarius appears to be constitutive, but can be greatly enhanced in the acidic environment. It has been presumed that ureolytic activity of S. salivarius strains isolated from caries-active site is greater than that of strains from caries-free site. However, no in vivo study has supported the presumption. The present study was performed to observe the ureolytic activity of S. salivarius strains isolated from different environments in the same individual, finding out whether the ureolytic activity is related to dental caries. For the purpose, S. salivarius strains were isolated from caries-active site (>C2), a caries-free site of the tooth, and the dorsum of the tongue of each of 50 patients having decayed teeth. The strains isolated from the patients who harbored S. salivarius in more than two sites were selected and then their ureolytic activities were measured. In order to examine clonal diversity of the strains , their ureC genes were amplified by polymerase chain reaction (PCR) and then restricted with EcoRV, and the protein profiles of the strains were compared by SDS-PAGE. The results were as follows :
1.Of 50 patients, 13 patients harbored S. salivarius in more than two sites; a total of 61 S. salivarius strain were isolated from the patients and selected for the study.
2.Of 17 isolates from the caries-active site of 9 patients harboring S. salivarius in more than two sites including carious lesion, 10 (58.8%) showed a high ureolytic activity (> 200㎛ol/min/mg). While, 19 out of 44 isolates (43.2% ) from the caries-free site of the teeth and the dorsum of the tongues of 13 patients were the strains with a high ureolytic activity.
3.Of 9 patients harboring S. salivarius in more than two sites including caries-active site, 6 patients were found to have the strains in the caries-active site showing a lower ureolytic activity than the strains in the other sites.
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