Convenient culture kit to estimate individual S.mutans and S.sobrinus levels

Objectives: The information regarding oral levels of mutans streptococci (MS) is important to evaluate susceptibility and activity of dental caries. The aim of this study is to construct a convenient culture kit which can estimate S.mutans and S.sobrinus levels without stereomicroscope, using two selective media (MSBG for MS and MSBGA for S.sobrinus). Methods: Brushing plaque samples from 40 young adults were prepared by the method of Neta et al. Selectivity test of the media was examined by spiral culture system using improved MSB medium and colony counting with a stereomicroscope. Three types of culture kits were prepared using 2 segmented plate, slide glass and small test tube, and those usefulness was examined as follows. The plaque samples were diluted, and inoculated on the MSBG and MSBGA media in kits with small cotton swab. After culture for 48-72 h, colonies formed were roughly counted with naked eye or loupe. S.mutans and S.sobrinus were evaluated as the difference between colony numbers on the both media and the colony numbers on MSBGA medium, respectively. Finally, both bacterial levels were classified into four grade of 0 to 3. Results: The selectivity of MSBG medium was almost same as that of the improved MSB medium (Detection ratios of non-MS were 0.82% and 0.67%, respectively), and the selectivity of MSBGA medium was excellent (Detection ratio of non-MS was 0.03%). The test-tube culture kit was superior to the segmented plate and slide glass culture kits in regard to operation and preservation. The estimation levels of S.mutans and S.sobrinus obtained by the test-tube culture kit showed good correlation with the bacterial counts obtained by the spiral culture method (Correlation efficiency: 0.89 and 0.93, respectively). Conclusion: Results suggest that the developed test-tube culture kit will be a good tool for caries risk assessment for clinical use.