Glycolytic activity of Streptococcus mitis grown in vitro and in gnotobiotic animals

Biochemical change exhibited by oral streptococci resulting from laboratory subculturing

The intent of this study was to assess the effects of continued laboratory subculturing on selected biochemical properties of oral streptococci freshly isolated from dental plaque. Six fresh isolates (3 Streptococcus mutans and 3 non-mutans) and 2 laboratory strains were subcultured daily for a total of 225 transfers, and cells were harvested every 75 transfers from duplicate batch cultures grown with glucose at a constant pH. Eleven biochemical properties were assayed with cells, membranes and cell-free extracts and the results subjected to statistical analysis for differences between the duplicate cultures and the various subcultures. In addition, the activity of 19 hydrolytic enzymes was assayed with the semiquantitative apiZYM system (Analytab products). The activity of zero-time samples varied by as much as 241-fold for a single property with particularly low activity for EIIglc of the phosphoenolpyruvate phosphotransferase system and cell-associated extracellular polysaccharide synthesis. The 3 S. mutans fresh isolates had higher activity in 8 of the 11 assays compared with the 3 non-mutans strains, with extracellular polysaccharide synthesis the most significant trait. Statistical analysis of the 2816 assays of the 11 traits for the 8 test strains at the 4 selected time intervals revealed considerable change in the activity of the test parameters. The most notable changes in the S. mutans strains over the 225 subcultures were significant increases in glycolytic activity and decreases in hydrophobicity and extracellular polysaccharide synthesis activity. Of the measured properties, lactate dehydrogenase and cell-associated extracellular polysaccharide synthesis activity were the most stable and H+/ATPase activity was the most variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptococcus mutans dextransucrase: stimulation by phospholipids from human sera and oral fluids

Serum, gingival crevicular fluid, and parotid, submandibular, and labial minor gland saliva from four individuals stimulated glucan formation from sucrose by the Streptococcus mutans strain 6715 dextransucrase (EC 2.4.1.5). At final dilutions of 1:10 all of the fluids stimulated crude enzyme preparations approximately 1.8-fold. The fluids stimulated the purified water-insoluble glucan-synthesizing form of the dextransucrase approximately 3.2-fold and the water-soluble glucan-producing form of the enzyme approximately 2.4-fold. The fluids all contained concentrations of stimulatory material that could be reduced to undetectable levels only after dilutions of greater than 1:1,000. The increased rates of glucan formation caused by the fluids and dextran were additive, indicating that stimulation by the fluids was primarily due to interactions with entities other than glucan primer molecules. In contrast, the elevated levels of glucan formation in the presence of the fluids was not further enhanced by the addition of lysophosphatidylcholine. Lysophosphatidylcholine purified from parotid and submandibular saliva by solvent extraction and thin-layer chromatography stimulated the dextransucrase as effectively as egg yolk lysophosphatidylcholine. Thus, phospholipids normally found in human oral fluids can enhance the activity of an enzyme believed to be directly associated with the cariogenic potential of S. mutans.

Sucrose metabolism by prominent members of the flora isolated from cariogenic and non-cariogenic dental plaques

Sucrose metabolism by resting-cell suspensions of pure cultures of representative members of the predominant cultivable flora isolated from cariogenic and non-cariogenic dental plaque was investigated by means of radiochemical techniques. Streptocococcus mutans utilized sucrose at a considerably faster rate than S. sanguis, S. mitis, Actinomyces viscosus, A. naeslundii, or Lactobacillus casei, forming lactic acid, intracellular polysaccharide, insoluble extracellular glucan, and lactic acid from intracellular polysaccharide catabolism at faster rates than the other bacteria. The Actinomyces formed more volatile acids than the streptococci, mostly acetic, and S. sanguis formed more soluble extracellular polysaccharide than the other bacteria. The metabolic activity of S. mutans resembled the pattern of sucrose metabolism of cariogenic plaque, whereas the metabolic activity of the Actinomyces species, the predominant members of non-cariogenic plaque flora, resembled the sucrose metabolism of non-cariogenic plaques.

Phosphoenolpyruvate-dependent glucose transport in oral streptococci

Streptococcus mutans, S sanguis, and S salivarius use a phosphoenolpyruvate (PEP)-dependent phosphotransferase system that results in phosphorylation of glucose at carbon 6. This enzyme system is not sensitive to fluoride. Glucose uptake into resting cell suspensions is sensitive to fluoride because of inhibition of intracellular PEP production. The glucose phosphotransferase system is constitutive in oral streptococci.