Marie-Louise Sund

The influence of Streptococcus mutans on adhesion of Candida albicans to acrylic surfaces in vitro

Adhesion of Candida albicans and Streptococcus mutans was studied by incubation of radiolabelled cells with acrylic test specimens in a chemically defined growth medium. Strep. mutans adhered firmly in the presence of sucrose, while C. albicans was only loosely attached to the acrylic in both glucose and sucrose media. Firm adhesion of C. albicans occurred when the yeast was incubated simultaneously with Strep. mutans, in the presence of sucrose. The adhesion of C. albicans was also stimulated by incubation with Strep. mutans culture supernatants. Adhesion was not affected by the presence of partially purified glucosyltransferase from Strep. mutans IB. Coaggregation between C. albicans and Strep. mutans upon growth in sucrose medium was observed by light and scanning electron microscopy. No coaggregation was observed in the presence of glucose.

Autolysis in Strains of Viridans Streptococci

Seven strains of viridans streptococci of the species Streptococcus sanguis, S. mutans and S. mitis were investigated for autolysis. The effect of pH, salt concentration and temperature on the autolytic process was studied in Na2HPO4/NaH2PO4 buffer. Whole cells and walls of all strains autolysed most rapidly at pH values above 7. Autolysis of whole cells of S. sanguis and one strain of S. mitis (ATCC15909) was maximal in 0-05 TO 0-2 M buffer, while the two S. mutans strains and S. mitis ATCC15912 showed maximal autolysis in 0-5 and 1-0 M buffers. Cultures harvested in the stationary phase of growth possessed only slightly decreased autolytic activity compared with those from the exponential phase. Whole cells autolysed more rapidly at 37 degrees C Than at 45 degrees C and 10 degrees C. Autolysis of isolated walls of three strains of S. mitis (ATCC903, ATCC15909 and ATCC15912) was maximal at pH 7-0 AND 7-5 and in 1-0 M buffers. Streptococcus mitis ATCC15909 also showed maximal lysis in 0-01 M and 0-5 M buffers. An endopeptidase action of the autolytic system of S. mitis ATCC15912 was indicated by the progressive release of soluble amino groups during autolysis of the walls. No release of reducing groups was observed. Several free amino acids were released during autolysis of these walls, alanine, lysine and glutamic acid being in greatest quanitity.

Arginine catabolism by strains of oral streptococci

Arginine catabolism via the arginine deiminase pathway was found in Streptococcus sanguis 903. Citrulline and ornithine were released from resting cells incubated with arginine, arginine‐containing peptides, or saliva. Maximum arginine catabolism by resting cells of S. sanguis 903 was found in the pH range 7–8 and at 45–48°C. Arginine deiminase activity was found in the cytoplasm and in the cell‐wall extract of this strain, while ornithine carbamoyltransferase activity was found in the cytoplasm and in extracts of cell walls and cytoplasmic membranes. Streptococcus mutans GS‐5 and Streptococcus sobrinus strains OMZ 176 and 6715 could release arginine from salivary peptides but were incapable of significant arginine catabolism.

Effect of Human Lysozyme on 2-Deoxyglucose Uptake by Streptococcus mutans and Other Oral Microorganisms

The effect of human urinary lysozyme (HUL) on 14C-2-deoxyglucose (14C-2DG) incorporation by a total of 20 strains of oral microorganisms, representing Streptococcus muta

Isoelectric focusing studies on the beta-fructofuranosidases and alpha-glucosidases of Streptococcus mitis.

Extracts of Streptococcus mitis ATCC 903 were analysed for beta-fructofuranosidase and alpha-glucosidase activities by isoelectric focusing in thin-layer polyacrylamide gels combined with zymogram procedures. Three bands of activity were visualized in the gels after incubation with sucrose (pI 4.05, 4.25 and 4.85) and three other bands after incubation with p-nitrophenyl alpha-D-glucopyranoside (pI 3.90, 4.45 and 4.65). The enzymes responsible for the reaction with sucrose were identified as beta-fructofuranosidases (EC 3.2.1.26) for the following reasons: identical enzyme bands were visualized in the gels after incubation with raffinose; no enzyme bands appeared in the gel after incubation with the alpha-glucosides maltose, turanose, trehalose and melezitose; and the soluble fraction hydrolysed sucrose to equimolar amounts of glucose and fructose.

Characterization of dextran glucosidase (1,6-a-D-glucan glucohydrolase) of Streptococcus mitis.

Dextran glucosidase (EC 3.2.1.70) isolated from cell extracts of Streptococcus mitis ATCC 903 was purified 925-fold by DEAE-Sephadex, Sephadex G-100 and hydroxylapatite chromatography. The enzyme showed normal Michaelis-Menten kinetics when tested with p-nitrophenyl-α-D-glucopyranoside (pNPG), dextran (MW 9,400) or isomaltose as substrates. The apparent Km values were 1.60, 4.95 and 15.7 mM, respectively. The molecular weight of the enzyme was estimated to 54,000 and the pi was 4.45. Among the metal ions tested (1 mM solutions), Hg2+ and Zn2+ inhibited the enzyme activity completely. In spite of an inhibiting effect of EDTA, no cationic metallic cofactor was found. Glucose exerted competitive inhibition of enzyme activity (KI = 2.5 mM). Optimal enzyme activity was found at pH 7.2 in the temperature range of 37–40 °C and at a low salt concentration (I = 0.06).

Purification and characterization of an aminopeptidase from Streptococcus mitis ATCC 903

An aminopeptidase isolated from the cytoplasmic fraction of a cell extract ofStreptococcus mitis ATCC 903 was purified 330-fold by ion-exchange chromatography, gel filtration, and hydroxyapatite chromatography. The partially purified enzyme had a broad substrate specificity. Twelve aminoacyl-ß-naphthylamide substrates were hydrolyzed and also several di-, tri-, tetra-, and pentapeptides and bradykinin. The enzyme hydrolyzed arginine-ß-naphthylamide at the highest rate. Optimal conditions for activity were at pH 7.0–7.2 and at 37–40°C. The molecular weight of the enzyme was estimated to be 93,000. The enzyme was activated by Co2+ ions. Hg2+ inhibited the activity completely. SDS, EDTA, urea, and pCMB also inhibited activity. Inhibition by EDTA could be completely reversed by dialysis and addition of Co2+ ions. Reducing agents, sodium fluoride, and PMSF had no effect on the activity of the enzyme. The isoelectric point of the enzyme was at pH 4.3. High substrate concentrations inhibited activity. Substrate inhibition increased in the presence of high concentrations of Co2+ ions.

Degradation of Streptococcus mutans Water-Soluble Glucans by Dextran-Glucosidase from Streptococcus mitis

Dextran-glucosidase EC 3.2.1.70 isolated from Streptococcus mitis ATCC 903 was tested for activity on water-soluble polysaccharides produced from sucrose by four Streptococ

Characterization of membrane-associated arginine aminopeptidase inStreptococcus sanguis 903

Extracts of cytoplasmic membranes ofStreptococcus sanguis 903 were analyzed for aminopeptidase activity by isoelectric focusing in polyacrylamide gel and enzyme staining with 16 different aminopeptidase substrates. A single aminopeptidase with specificity for aminoterminal arginine was detected. The enzyme was stimulated by dithiothreitol andβ-mercaptoethanol. Urea, sodium dodecyl sulfate (SDS), andp-chloromercuribenzoate were inhibitory. Metal ions had little or no effect on activity, except that Hg2+, Cu2+, and Ni2+ were inhibitory. The pH optimum for activity was at 7.2. The molecular mass estimated by SDS-polyacrylamide gel electrophoresis was 170 kDa.

Glucose Incorporation by Human Dental Plaque Bacteria

The incorporation of 14C-sugars was measured in dental plaque suspensions (pH 6.8) incubated at 37 °C. The initial rates of incorporation in 0.1 m M glucose, 0.1 m