Five strains of were grown in continuous culture with either a limited supply or an excess of glucose. Proteins secreted into the extracellular fluid by strains C67-1, 3209 and K1 rapidly catalysed the synthesis of insoluble glucan from sucrose (mutansucrase activity). The culture fluid from strains Ingbritt or C67-25 catalysed the synthesis of soluble glucan (dextransucrase activity) and fructan, but little or no mutansucrase activity was detected. The strains which secreted active mutansucrase readily colonized a smooth hard surface during growth in batch culture and were more cariogenic in pathogen-free rats than those which secreted little mutansucrase activity. There was no similar correlation between fructosyltransferase, dextransucrase or total glucosyltransferase activity and either adherence or cariogenicity. We conclude that the ability to catalyse insoluble glucan synthesis is a major determinant of the cariogenicity of strains.


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