| Purpose：Dental caries induced by streptococcus mutans was one of the most prevalentchronic infectious diseases. Among all the physiological traits, three played crucialroles in S.mutans＇pathogenicity. They were adhension，acidogenesis and aciduricity.Fluoride could combine directly with H+-ATPase of streptococcus mutans to inhibitit,s activity，to reduce the proton permeability of cell membrane，to improve theaciduricity, so fluoride was widely used in clinic. But with the local application of ahigh concentration and frequency of fluoride, fluoride resistant strains were selected.To explore the mechanism of fluoride resistant strains became a new researchdirection. Similarly, the pathogenicity of fluoride-resistant strain of S.mutants reliedon adhension，acidogenesis and aciduricity. In the S.mutants，glnR and brpA weretranscription factors.The study showed that the expression of glnR involved in theregulation of streptococcus mutans,nitrogen metabolism and acid repression, theexpression of brpA involved in the cell division and the formation of bacterialbiofilm, which were closely related with the regulation of aciduricity. In this study,Using molecular biology techniques, we detected the real-time expression of glnRand brpA in the fluoride-resistant strain and their parental strain of S.mutants tocompare their differences. This study revealed a deeper acid mechanism ofstreptococcus mutans， but also provided a new theoretical guidance for theprevention and treatment of dental caries.Methods：1. The induction and identification of the fluoride-resistant strain of S.mutans． S.mutans administered in50ug/ml NaF additive until1000ug/ml NaFfluoride resistant strains obtained from the BHI solid medium, detecting by gramstain and16S rRNA identification.2. The determination of growth curved in the fluoride resistant strain and theirparental strain of S.mutants. To culture them in BHI liquid medium for48hours，measuring OD600intervals of8hours and drawing two bacteria growth curve.3. Detecting gene expression of glnR and brpA in the fluoride resistant strain andtheir parental strain of S.mutants by real-time quantitative PCR. To extractrespectively24hour and48hour of S.mutans and fluoride resistant strains of totalRNA, using the real-time fluorescent quantitative PCR to test the expression ofgenes，then to analyse the results with spss17.0.Results：1. UA159-FR grew well in the BHI solid medium and microscopic observationof colonial morphology was short hammer in Gram staining，so morphologyconformed to the description of streptococcus mutans; UA159-FR was similar withstreptococcus mutans in99%by using16S rRNA identification technology.2. In S.mutans and fluoride resistant strains，the gene expression of glnR andbrpA in48hour was difference in the gene expression in24hour，and the geneexpression of48hour was more than24hour.3. In S.mutans and fluoride resistant strains，the gene expression of glnR hadobvious differences in24hour, and the former was superior to the latter; they alsowere differentially in48hour, and the latter was superior to the former.4. In S.mutans and fluoride resistant strains，the gene expression of brpA had nodifference in24hour; but they were differences in48hour, and the latter wassuperior to the former.Conclusion：1. UA159-FR was induced successfully in vitro, it,s still streptococcus mutansidentified by the analysis of morphology and gene.2. In S.mutans and fluoride resistant strains，24hour was their logarithmic phase;48hour was their stationary phase.3. In the stationary phase，the gene expression of glnR and brpA in fluorideresistant strains was higher than that of streptococcus mutans, showing glnR andbrpA genes associated with the enhancement of aciduricity in fluoride resistantstrains. |
