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G Bourgeau

Publications and source records attributed to G Bourgeau.

9 recordsLinked to original sources
PubMed1996

Emergence of multiple xylitol-resistant (fructose PTS-) mutants from human isolates of mutans streptococci during growth on dietary sugars in the presence of xylitol.

The growth inhibition of mutans streptococci is one of the proposed mechanisms of action of xylitol, a caries-preventive natural carbohydrate sweetener. Xylitol is taken up and accumulated as non-metabolizable, toxic xylitol phosphate via a constitutive fructose PTS, and selects, during in vitro growth at the expense of glucose, for natural xylitol-resistant mutants that lack constitutive fructose PTS activity. Since long-term xylitol consumption leads to the emergence of xylitol-resistant mutans populations in humans in an oral environment containing sugars of dietary origin, we wanted to test the hypothesis that xylitol-resistant cells could be selected from mutans streptococci strains during in vitro growth on fructose, sucrose, or lactose. Three laboratory strains and three fresh mutans streptococcal isolates were repeatedly transferred in trypticase-yeast extract medium supplemented with glucose, fructose, sucrose, or lactose in the presence and absence of xylitol. Depending on the growth sugar, the presence of xylitol resulted in the selection of xylitol-resistant populations for several of the six strains tested, but not necessarily in the presence of all four sugars. All six strains rapidly became xylitol-resistant when grown on glucose in the presence of xylitol. All three fresh isolates became xylitol-resistant after 9 to 16 transfers in the presence of fructose or sucrose plus xylitol, while none of the laboratory strains became xylitol-resistant after 16 transfers in the presence of these sugars. The growth rates of 12 xylitol-resistant mutants in the presence of eight sugars suggested the existence of various types of xylitol-resistant mutants. The data partially explain the occurrence of xylitol-resistant mutans populations in long-term xylitol consumers and suggest a mechanism consistent with a selection process. Since various preliminary results suggest that xylitol-resistant natural mutants may be less virulent and less cariogenic than their parent strains, this selection process may alter, for the better, the mutans streptococci population of the plaque and play a role in the caries-preventive action of xylitol.

Culture Media↗
PubMed1992

Cloning, expression, and sequencing of a protease gene (tpr) from Porphyromonas gingivalis W83 in Escherichia coli.

Porphyromonas gingivalis is a highly proteolytic organism which metabolizes small peptides and amino acids. Indirect evidence suggests that the proteases produced by this microorganism constitute an important virulence factor. In this study, a gene bank of P. gingivalis W83 DNA was constructed by cloning 0.5- to 20-kb HindIII-cut DNA fragments into Escherichia coli DH5 alpha by using the plasmid vector pUC19. A clone expressing a protease from P. gingivalis was isolated on LB agar containing 1% skim milk. The clone contained a 3.0-kb insert that coded for a protease with an apparent molecular mass of 64 kDa. Sequencing part of the 3.0-kb DNA fragment revealed an open reading frame encoding a protein of 482 amino acids with a molecular mass of 62.5 kDa. Putative promoter and termination elements flanking the open reading frame were identified. The activity expressed in E. coli was extensively characterized by using various substrates and protease inhibitors, and the results suggest that it is possibly a thiol protease.

Amino Acid Sequence↗
PubMed1990

Aggregation of Actinomyces strains by extracellular vesicles produced by Bacteroides gingivalis.

The aggregation of Actinomyces viscosus and Actinomyces naeslundii with extracellular vesicles of Bacteroides gingivalis was studied. Factors influencing the aggregation phenomenon were examined. L-Arginine was found to effectively inhibit aggregation as was an antibody preparation directed against a B. gingivalis surface hemagglutinin. Aggregation occurred over a wide pH range and did not seem to be affected by high salt concentrations or the presence of carbohydrates. Treatment of the vesicle preparation with proteases, sodium dodecyl sulphate, and high temperatures diminished or eliminated aggregation, while similar treatment of the Actinomyces had no effect on aggregation.

Actinomyces↗
PubMed1984

Properties of oral asaccharolytic black-pigmented Bacteroides.

Bacteroides endodontalis, a newly described asaccharolytic black-pigmented Bacteroides, along with the other two recognized species of this group (B. gingivalis and B. asaccharolyticus) were studied for their susceptibility to various dyes and inhibitory agents and for some of their enzymatic activities to facilitate differentiating between them. Bacteroides endodontalis resembles B. asaccharolyticus physiologically except for the fact that the former cannot grow on media containing methylene blue, neutral red, or 3% sodium chloride, whereas B. asaccharolyticus can. On the other hand, B. endodontalis and B. gingivalis can grow on a medium containing Congo red while B. asaccharolyticus cannot.

Bacteroides↗
PubMed1983

Control of sugar utilization in the oral bacteria Streptococcus salivarius and Streptococcus sanguis by the phosphoenolpyruvate: glucose phosphotransferase system.

Three different Strep. salivarius (G2, G5 and G29) and two Strep. sanguis (GS3 and GS12) mutants affected in the phosphoenolpyruvate: glucose phosphotransferase system were selected on agar plates containing lactose and 2-deoxyglucose. All 5 were defective in a membrane-bound component of the transport system and grew less rapidly than the parent strain in 5 mM glucose-containing medium. Mutants G2 and G29 grew poorly in the presence of 5 mM mannose. Growth on mixed substrates revealed that the mutants and wild-type parents behaved differently. Wild-type strains in medium containing glucose plus another sugar (lactose, galactose, melibiose, raffinose or trehalose for Strep. salivarius and lactose, galactose or trehalose for Strep. sanguis) always exhausted most of the glucose before utilizing the other sugar. The mutants used the second sugar concurrently or preferentially to glucose. In medium containing glucose plus fructose or mannose, the wild types consumed both sugars concurrently whereas the mutants utilized the second sugar before glucose. Mutants G2 and G5 were insensitive to repression by fructose and released glucose into the medium when grown in the presence of 0.4 per cent lactose. Mutant G5 also released galactose. Sugar release was not detected with the wild types. The Strep. salivarius mutants contained normal levels of glucokinase and beta-galactosidase but G5 was almost totally devoid of galactokinase activity after growth on lactose. On galactose, the activity was restored. It seems that the phosphoenolpyruvate: glucose phosphotransferase system is involved in the regulation of sugar utilization in these two streptococci.

Glucose↗
PubMed1983

Phenylacetic acid production by Bacteroides gingivalis from phenylalanine and phenylalanine-containing peptides.

Phenylacetic acid production and growth of Bacteroides gingivalis were directly proportional to the trypticase content of the medium. L-Phenylalanine enhanced phenylacetic acid production; 5 mg L-phenylalanine per millilitre stimulated maximum production of phenylacetic acid. Peptides (2-4 amino acids) containing L-phenylalanine also stimulated phenylacetic acid production as did phenylpyruvic acid. Resting cell suspensions of B. gingivalis also produced phenylacetic acid when incubated aerobically in the presence of L-phenylalanine and phenylpyruvic acid. Hydrocinnamic acid (3-phenylpropionic acid) and phenyllactic acid were also produced by resting cell suspensions. Our results suggest that L-phenylalanine and phenylpyruvic acid are both precursors to phenylacetic acid.

Bacteroides↗
PubMed1982

Production of phenylacetic acid by anaerobes.

We tested 388 strains of anaerobes from 17 genera for the production of phenylacetic acid. The compound was found in only two genera (Bacteroides and Clostridium) but not within all the species of these genera.

Anaerobiosis↗
PubMed1976

Dextran-mediated interbacterial aggregation between dextran-synthesizing streptococci and Actinomyces viscosus.

Streptococcus sanguis and Streptococcus mutans bind to the surface of Actinomyces viscosus, producing large microbial aggregates. Aggregates form rapidly and are not easily dissociated by vigorous mixing. The binding is mediated by dextran. Glucose-grown streptococci will not aggregate unless they are first mixed with high-molecular-weight dextran. Aggregation is induced with dextrans isolated from Leuconostoc, S. sanguis, or S. mutans. Sucrose-grown streptococci will adhere to A. viscosus without the addition of an exogenous source of dextran. A. viscosus will bind dextran and then bind glucose-grown streptococci. Aggregation occurs over a wide pH range and is dependent on cations. The aggregating activity of A. viscosus is both protease and heat sensitive. The aggregating activity of S. sanguis is heat stable but sensitive to dextranase.

Actinomyces↗