关键词: L-精氨酸, 变异链球菌, 戈登链球菌, gtfB基因, SMU.150基因, nlmD基因

Abstract: Objective    To study the effect of L-arginine on Streptococcus mutans（S.mutans） and Streptococcus gordonii（S.gordonii）in vitro. Methods    The study was conducted from June 2022 to November 2023 at the Public Laboratory Platform，Department of Medicine，Jianghan University. Bacteria were categorized into S.mutans group，S.gordonii group，and S.mutans & S.gordonii group based on individual or mixed cultures. After treatment with different mass fractions（2.00%，1.00%，0.10%）of L-arginine，the optical density values at wavelength 620 nm（OD620）after 24 h，48 h and 96 h of bacterial culture in S.mutans and S.gordonii groups，as well as the relative expression levels of bacteria and S.mutant related genes（gtfB，SMU.150，nlmD）in S.mutans & S.gordonii group were detected，and compared with the blank control（no L-arginine treatment）with the same culture time. Scanning electron microscopy was used to observe the effects of different mass fractions（2.00%，1.00%，0.10%）of L-arginine on the process of plaque biofilm formation and the formed plaque biofilm of S.mutans group，S.gordonii group and S.mutans & S.gordonii group. Results    In S.mutans and S.gordonii groups，the OD620 values of the 2.00% and 1.00% L-arginine-treated bacterial fluids decreased significantly after 24 h of culture compared with those of the blank control fluids at the same culture time，and the differences were statistically significant（all P < 0.05），whereas the OD620 values of the bacterial fluids treated with 0.10% L-arginine after 24 h，48 h and 96 h of culture were compared with the blank control bacterial fluids at the same culture time，and the differences were not statistically significant（all P > 0.05）. In S.mutans & S.gordonii group，the relative expression of S.mutans and S.gordonii was significantly reduced after 24 h of culture after being treated with 2.00% and 1.00% L-arginine，and the relative expression of S.mutant was significantly reduced while that of S.gordonii was significantly increased at 24 h after being treated with 0.10% L-arginine. The relative expression of gtfB，nlmD and SMU.150 was significantly reduced after 24 h of L-arginine treatment for all mass fractions，and the differences were all statistically significant（all P < 0.05）. Scanning electron microscopy showed that the plaque biofilms of S.mutans，S.gordonii and S.mutans & S.gordonii groups became loose after 24 h of culture after being treated with 2.00% and 1.00% L-arginine，while after treatment with 0.10% L-arginine，the plaque biofilms of S.gordonii and S.mutans & S.gordonii groups showed no significant change，but the growth of plaque biofilms of the S.mutans group was inhibited. Conclusion    The 2.00% L-arginine and 1.00% L-arginine have inhibitory effects on both S.mutans and S.gordonii；0.10% L-arginine can inhibit the growth of S.mutant plaque biofilm and increase the relative content of S.gordonii in mixed plaque biofilm. L-arginine can help to construct a healthy oral plaque microecology，which provides a new direction for the prevention of caries.

Key words: L-arginine, Streptococcus mutans, Streptococcus gordonii, gtfB gene, SMU.150 gene, nlmD gene