Detection Of Mutation In The Acid-resistant Gene Fhs Of The Fluoride-resistant Strain Of Streptococcus Mutans

Caries is dentine disease infected by bacteria. Streptococcus mutans is recognized main cariogenic bacteria.Fluoride is extensively used for caries prevention. Its effect on cariogenic bacteria is one of important mechanisms for the caries prevention by fluoride. But long-term topical applications of high-concentration fluoride may lead to growth of F-resistant strains. F-resistant strains depress the effect of topical applications of fluoride and are more difficult to be restrained than the parent strains. The appearance of F-resistant strains bring the new issue for caries prevention by fluoride. Studying the F-resistant strains can make us know the changes of cariogenicity of S. mutans after fluoride - resistant mutation beforehand, afford experimental evidence for using fluoride rationally and finding new medication.Streptococcus mutans is recognized as cariogenic bacterium whose cariogenicity is related with acidogenic ability and acid resistance. It is reported that the acidogenic ability and acid resistance of S. mutans increased after S. mutans fluoride - resistant mutated. Acid resistance is that bacteria can continue producing acid and performing its function under low pH value,which includes constitutive acid tolerance and acid tolerance response. Its acid resistance is decided by many genetic factors. Some acid-resistant genes of S. mutans have been separated and cloned now. In this report we study the gene: fhsThe gene encodes formyl-tetrahydrofolate synthetase (Fhs) from both prokaryotic and eukaryotic sources. In many bacteria, Fhs catalyzes the formation of 10-formyl-tetrahydrofolate, which is used directly in purine biosynthesis and formylation of Met-tRNA and indirectly in the biosynthesis of methionine, serine, glycine, and thymine. For ATP is the substrate of H+-ATPase affection,we predicted that themutation induced the abnormal of acid resistance which because the purine synthesis abnormal cause ATP synthesis abnormal,which induced H+-ATPase remove H+ abnormal.It is repored that The genotypes of F-resitant strains of S. mutans have been changed and may comprise several gene mutations,but idiographic part of gene mutation is not known. In this study, we designed the primers according to fhs's sequence of S. mutans from GenBank database to do PCR. So we got the fhs's partial sequence of the F-resitant strains. We made the acquired sequences connected with PGEM-T vector and sequenced them. We compared the sequence with it from GenBank database by blastn and found that fhs's sequence has 6 bases to be changed. The results were submitted to American GenBank, and the accession number is EF405868. Fhs's mutation is point mutation and the substitution cause two changes in the amino acid sequence of the protein. These changes are Arg→Gln and Val→Ile. We can guess that the mutations of acid-resistant gene ffh relate to the advance of the acid-resistant characteristic of the fluoride-resistant strain of streptococcus mutans.As is extensively used for preventing caries,fluoride is challenged by F-resistant strains.So we have to find new medicine for caries preventive,fluoride and we should use fluoride in right way.The mechanism of fluorid to prevent caries is that it can effect both teeth and bacteria.It is reported vaccine for streptococcus mutans can prevent caries.With the development of the technology of molecular organism,we have got great achievement on vaccine. DNA vaccine is the great progress in human preventive medicine. It's theory is making exogenous gene imported into host cell, inducing host immune system to carry out immune reaction. The study on acid-resistant gene fhs prefers new direction for DNA vaccine and has important significance.