Abstract: PURPOSE: To evaluate the effect of S.mutans luxS gene on mixed-species biofilms communities. METHODS: Biofilms were formed by S. mutans (wild type strain, its luxS overexpression strain and luxS knockout strain) and Lactobacillus acidophilus (ATCC4356) with a ratio of 1:1 at 37℃ for 4 h, 14 h and 24 h. MTT assay was used to detect the quantification of the biofilms formed. The structures of biofilms were observed under confocal laser scanning microscopy after 24 h, and expression of biofilm-related genes (ftf, smu630, brpA, gbpB, gtfB, vicR, comDE and relA) was investigated by real-time PCR. Statistical analysis was performed with SPSS17.0 software package. RESULTS: The results showed that biofilm formed by S. mutans(wild type strain, its luxS overexpression strain and luxS knockout strain) and L.acidophilus after 14 h were 0.481±0.024, 0.591±0.023 and 0.279±0.019, respectively. The same findings were present after 24 h, the biofilm formed by S.mutans overexpression strain with L.acidophilus was higher than wild type strain, and the biofilm formed by knockout strain significantly decreased; but there was no significant difference at 4 h time points. CLSM images revealed that both S.mutans overexpression strain and its wild type strain tended to aggregate into distinct clusters and dense structures, whereas the luxS knockout strain appeared relatively sparse. Compared with wild type strain, all of the genes examined were upregulated in the biofilms formed by the overexpression strain, and were downregulated in the biofilms formed by the luxS mutant strain in mixed-species biofilm. CONCLUSIONS: S.mutans luxS gene can affect mixed-species biofilm formation with L.acidophilus, which provides evidences for further study.

Key words: Streptococcus mutans, Biofilm, luxS gene, Lactobacillus acidophilus