Objective: To investigate the difference in the expression ability of fructosyltransferase（FTF） in vitro in a non-stressful environment between a high temperature requirement serine proteinase A（HtrA） gene-deficient Streptococcus mutans strain and a HtrA high-virulent S. mutans strain with high cariogenicity. Methods: A high-virulent S. mutans strain obtained in our previous study

an HtrA gene-deficient strain constructed based on it

and an international standard strain

S. mutans UA159

were selected and cultured in brain-heart infusion（BHI）broth for 16 h. The real-time quantitative PCR detection system was used to determine the amplification of FTF gene in the three strains. The relative quantitative analysis—2-△△Ctmethod was used to calculate and compare the relative expression of FTF gene in the three strains. Results: The FTF gene expression in the HtrA high-virulent strain was23.588 times that in the HtrA gene-deficient strain

while that in the UA159 standard strain was 10.556 times that in the HtrA gene-deficient strain. Conclusion: The expression of FTF in cariogenic S. mutans is regulated by HtrA.