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Chapter 31 : Role of Sucrose Metabolism in the Cariogenicity of the Mutans Streptococci
Dental caries constitutes the most common, and very likely the most expensive, of human diseases. Two members of the mutans streptococci (MS), Streptococcus mutans and S. sobrinus, are the most common human cariogenic pathogens. Several enzymes or enzyme systems in the MS are associated with the metabolism of sucrose, and most may be involved in the virulence of these oral pathogens. All MS have glucosyltransferases (GTFs) responsible for the synthesis of extracellular homopolymers of glucose which may be water soluble or insoluble, depending on the proportion of α-1,3 linkages present. The amino acid sequences of the proteins predicted by the respective scrA genes shared only 45% identity, whereas the corresponding sucrose phosphate hydrolase (SPH) proteins predicted by the scrB genes shared ~ 70% amino acid identity. An extremely useful feature of recombinant DNA technology is the ability to manipulate cloned genetic determinants from a particular organism, to replace the wild-type determinant with the altered one, and then to test the effects of such manipulation on the phenotype associated with that determinant. Such a process requires an ability to introduce DNA into the organism under study. Finally, the availability of gene transfer systems and appropriate vector molecules will permit comparative analyses of the regulation of sucrose metabolism in the MS.