[Effect of Lipoteichoic Acid Synthesis-Related Gene dltD on Acid Tolerance of Highly Cariogenic Strains of Streptococcus mutans].

Objective: To study the role and possible mechanism of dltD in the acid tolerance of Streptococcus mutans 593 (SM593), and to provide a theoretical basis for the ecological prevention and control of dental caries by constructing the dltD gene deletion strain of SM593 (SM593-ΔdltD). Methods: 1) SM593-Δ dltD was constructed by homologous recombination. 2) The growth curve of SM593 dltD and SM593-Δ dltD under different pH culture conditions was drawn by the automatic growth curve analyzer to compare their acid tolerance. Colony forming unit (CFU) at different time points was used to calculate the survival rate and to compare the acid tolerance response (ATR) of SM593 and SM593-Δ dltD. 3) Under different pH conditions, glycolysis experiments, proton permeability test and H +-ATPase activity test were conducted to make preliminary exploration into the mechanisms of how dltD gene deletion may affect acid tolerance. Results: 1) PCR and sequencing results showed that the SM593-Δ dltD was constructed successfully. 2) With decreasing pH value of the culture medium, the growth of SM593-Δ dltD slowed down. When the pH value of the culture medium was 5.0, SM593-Δ dltD was not allowed to grow, and its acid tolerance was lower than that of SM593. Compared with SM593, the ATR capability of SM593-Δ dltD was decreased. 3) SM593 dltD and SM593-Δ dltD did not show obvious difference in their glycolysis ability under different pH conditions. Compared with SM593 dltD, the proton permeability of SM593-Δ dltD under different pH conditions was increased significantly (P<0.05), and H +-ATPase activity decreased significantly (P<0.05). Conclusion: Compared with SM593 dltD, SM593-Δ dltD showed obvious decrease in acid tolerance, which may be caused by the significant increase in proton permeability and significant decrease in the H +-ATPase activity induced by the deletion of the dltD gene, hence reducing its ability to maintain intracellular pH homeostasis.

[Evaluation of the in vitro cariogenic potential of Streptococcus mutans (serotype C) strains isolated from caries-free and -active people: the ability of acidogenicity].

OBJECTIVE: To investigate the ability of acidogenicity of S. mutans (serotype C) strains isolated from the people with different caries experience. METHODS: Same density solutions of all isolated S. mutans were made and cultured in different pH TPPE liquid for the same period of time. Terminal pH of the solutions was measured. The values of delta pH were compared. RESULTS: Significant difference of acidogenicity was observed between the strains of different genotypes isolated from the same person. The ratio of high acidogenicity isolates harbored in caries-active people was greater than that of caries-free people; a significant difference was noted (P<0.05). CONCLUSION: The high cariogenicity of isolated S. mutans strains of caries-active people shows a close relationship with the high acidogenicity of the isolated S. mutans (serotype C) strains.

[Effect of the self-etching adhesives system on human pulp fibroblast].

OBJECTIVE: To compare and evaluate the biocompatibility of three kinds of dentin bonding agents Xeno III (XO), Adper Prompt (AP), Single bond2 (SB) through cell culture in vitro. METHODS: Three kinds of dentin bonding agents (XO, AP, SB) were applied on the surface of the dental slices which were 5.0 mm in diameter and 0.5 mm in depth. By immersing the slices into the DMEM culture medium, the maceration extracts were obtained. Normal dental pulps of teenagers were collected and human pulp fibroblast was cultured using tissue explant method. The fifth generation pulp cells were exposed to culture medium containing different concentrations of maceration extracts (100.0%, 50.0%, 25.0%, 12.5%) for 24, 72, 120 h. At last, MTT method was used to evaluate the cytotoxicity of the dentin bonding agents on human pulp fibroblast. RESULTS: The results showed that all three kinds of dentin bonding systems had cytotoxicity to human pulp fibroblast in different degree in vitro. The cytotoxicity of XO and AP was less than SB. The difference was statistically significant (P<0.05). CONCLUSION: The results of cell culture in vitro indicated that total-etching adhesives system has more irritation to pulp than self-etching adhesives system.