Sucrose Metabolism in Resting-Cell Suspensions of Caries-Associated and Non-Caries-Associated Dental Plaque

ABSTRACT

Small specimens of cariogenic plaque (CP) and non-cariogenic plaque (NCP) from the same tooth were individually dispersed in buffer, divided equally, and incubated for 45 min with [¹⁴C]sucrose uniformly labeled either in the glucosyl moiety or the fructosyl moiety. Sucrose metabolism was analyzed periodically during an anaerobic incubation at 37°C. Radiochemical techniques were devised to analyze formation of lactic acid, soluble extracellular polysaccharide, total cell-bound and insoluble products, intracellular polysaccharide, lactic acid from intracellular polysaccharide catabolism, insoluble extracellular glucan, CO₂, total volatile acids, individual volatile acids, and rates of sucrose consumption. The contribution of the glucosyl and fructosyl moieties of sucrose to each metabolic by-product was determined. All of the metabolic data were adjusted to the size of the plaque specimens as determined by colony-forming units, Coulter counter particle counts, and fluorometric protein analyses. Both types of dental plaque transformed from 70 to 80% of the consumed sucrose into lactic acid and cell-bound and insoluble products, primarily intracellular polysaccharide and extracellular glucan. Volatile acids accounted for most of the remaining by-products. CP metabolized significantly more sucrose than NCP and consequently produced significantly higher levels of each metabolic by-product. High levels of Streptococcus mutans were found in CP (averaging 40% of colony-forming units), whereas it was virtually absent in NCP. Actinomyces and S. sanguis levels were distinctly higher in NCP. NCP harbored more anaerobes and dextranase-forming microorganisms than CP.