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R R Russell

Publications and source records attributed to R R Russell.

At least 55 records · Page 3Linked to original sources
PubMed1995

Identification and genetic characterisation of melibiose-negative isolates of Streptococcus mutans.

Streptococcus mutans is frequently identified on the basis of phenotypic characteristics such as the ability to ferment carbohydrates. The usefulness of some of these identification tests may be limited in the case of isolates which are atypical with regard to their fermentation properties. We previously identified isolates of S. mutans which were unable to ferment melibiose, a characteristic which is included in some typing schemes. In all of these isolates there was a large chromosomal deletion which included the multiple sugar metabolism (msm) operon which encodes several genes involved in the uptake and metabolism of a number of sugars including melibiose. In the present study, sugar fermentation tests, ribotyping, colony hybridisation with DNA probes and polymerase chain reaction (PCR) were used to investigate the relatedness of these atypical isolates. The PCR and colony hybridisation procedures were based on amplification and detection of two genes: the wapA gene which encodes a surface protein found in all S. mutans strains and the gtfA gene which lies within the msm operon. The colony hybridisation and PCR results confirmed loss of the gtfA gene in the melibiose-negative isolates. Three new melibiose-negative isolates were also identified, but in only 2 of these was the gtfA gene absent, the third did not appear to have lost this region of the chromosome. Biotyping, as well as ribotyping based on an EcoRI digest of chromosomal DNA, revealed that the melibiose-negative isolates fell into a number of distinct groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Outer Membrane Proteins↗
PubMed1994

Analysis of a primer-independent GTF-I from Streptococcus salivarius.

A glucosyltransferase (GTF) gene, designated gtfL, from Streptococcus salivarius was cloned and expressed in Escherichia coli and its nucleotide sequence determined. The GTF-L enzyme catalysed the synthesis of water-insoluble glucan in a primer-independent manner. The nucleotide sequence and derived amino acid sequence of GTF-L were similar in size and domain structure to previously sequenced glucosyltransferases. However, a 464-bp region of high variability was identified which could be selectively amplified from strains of S. salivarius by the polymerase chain reaction and could therefore form the basis for species identification. No sequence-specific motifs related to the solubility and linkage of the glucan product or its need for a dextran primer could be ascertained.

Amino Acid Sequence↗
PubMed1994

Identification and characterisation of two extracellular proteases of Streptococcus mutans.

Streptococcus mutans was shown to produce two extracellular proteases capable of degrading both gelatin and collagen-like substrates. These enzymes have molecular masses of 52 and 50 kDa when analysed by SDS-PAGE. Both enzymes were inhibited by EDTA, but not by a range of other inhibitors with different specificities, indicating that they are metalloproteases. The activity of EDTA-inactivated enzymes could be restored by the addition of manganese and zinc. The identical inhibition and restoration profiles of the two enzymes suggest that one of the proteases may be a degradation product of the other.

Chromatography, Gel↗
PubMed1994

The application of molecular genetics to the microbiology of dental caries.

The introduction of techniques for the manipulation of DNA in vitro has had an enormous impact on progress in every area of biological research. In the case of oral microbiology, the first reports on the application of molecular genetics to streptococci started to appear in the early 1980s, and it is now more than 10 years since the first paper describing cloning and expression of a gene from Streptococcus mutans in another bacterium was published. The purpose of this review is not to provide a resumé of all the work that has been done on the molecular biology of oral bacteria; indeed, we are approaching the stage when a comprehensive survey of work on all oral bacteria is no longer feasible--for instance, over 40 genes have now been cloned and sequenced from S. mutans alone--but rather to illustrate examples of how the new techniques have been applied to give novel approaches and insights into old problems, or expand into new directions. The great majority of published work so far relates to streptococci, and many aspects have been covered in previous review articles [Curtiss, 1985; Russell, 1991], the most recent thorough review being that by Kuramitsu [1993]. Discussion of molecular biology is now so all-pervasive that most readers will be familiar with many of the basic terms, but it may be worth clarifying some of the main points during the course of this article. For total novices, the short book by Brown [1990] forms a useful introduction. A number of recent articles have reviewed recent research on plaque formation [Kolenbrander and London, 1993] and the mutans streptococci in particular [Loesche, 1986], while Freedman et al. [1981] and Tanzer [1992] have summarised the information derived from a genetic approach to oral microbiology before the advent on in vitro manipulation of DNA.

Bacteria↗
PubMed1994

Incorporation of bacterial inhibitor into resin composite.

Attempts to produce resin composite with antibacterial properties by incorporation of an antibacterial agent such as chlorhexidine have been reported, but problems can arise due to release of the inhibitory agent from the composite. Such problems may include toxic effects, influence on mechanical properties, and loss of effectiveness. A new monomer, methacryloyloxydodecylpyridinium bromide (MDPB), was synthesized by combining an antibacterial agent and methacryloyl group. The monomer was incorporated into resin composite to develop a non-releasing antibacterial composite. The ability of composite incorporating MDPB to inhibit growth and plaque accumulation by Streptococcus mutans in vitro was assayed, elution of antibacterial components from the material was investigated, and the influence of incorporation of MDPB on the mechanical properties of composite was studied. Uncured MDPB revealed antibacterial activity against S. mutans and six other species of oral streptococci, with the minimum inhibitory concentration for S. mutans being comparable with that of triclosan. After composite incorporating MDPB was cured, no elution of the antibacterial components was observed from the material, even after 90 days' immersion in water or other solvents. Growth of S. mutans on agar under specimens of MDPB-containing composite was inhibited compared with controls. In a bacterial accumulation study, S. mutans accumulated to a lesser degree on the surface of composite incorporating MDPB (p < 0.05) than on control. Incorporation of MDPB had no significant influence on the mechanical properties of the composite.

Analysis of Variance↗
PubMed1994

Control of specific plaque bacteria.

The Specific Plaque Hypothesis posits that particular bacteria are of unique importance in the etiology of dental caries and periodontal diseases, and a logical conclusion is that these bacteria should be the targets for our 'magic bullets' in devising plaque-control methods. This paper considers the development of preventive measures based on understanding of the significance of particular bacterial species and the properties of those bacteria. Knowledge of the importance of specific organisms as mediators of disease and molecular studies on the properties of potential virulence factors may reveal potential targets for inhibition, blocking by synthetic analogues, or functional inactivation by antibodies.

Actinomyces↗
PubMed1993

Identification of Streptococcus mutans antigen D as the HPr component of the sugar-phosphotransferase transport system.

Extraction of Streptococcus mutans with the detergents HECAMEG and lauroyl sarcosinate preferentially extracted antigen D, previously identified as a low molecular mass wall-associated protein. Western blotting with specific antisera was used to demonstrate that this antigen is the HPr component of the sugar-phosphotransferase transport system. Non-denaturing electrophoresis indicated that HECAMEG selectively extracted only one of the two forms of HPr. It is suggested that this form of HPr may have a specific cell surface location.

Antigens, Bacterial↗
PubMed1993

Comparison of helium dilution and nitrogen washout measurements of functional residual capacity in premature infants.

Comparison has been made of measurements of functional residue capacity (FRC) by a helium gas dilution (He) and a nitrogen washout (N2) technique. Twenty infants (median gestational age, 29.5 weeks) were studied at a median postnatal age of 25 days. No infant was oxygen dependent. The coefficient of repeatability of FRC (He) was 6.4 mL/kg and of FRC (N2), 6.3 mL/kg. The coefficient of repeatability of the two methods combined was 13.8 mL/kg. In 10 infants the results of two techniques differed by more than 20% of the mean FRC; those infants were born at a significantly earlier gestation than the rest of the cohort (P < 0.01). We conclude that, except in very immature infants, techniques for measuring FRC (He) and FRC (N2) yield reproducible and comparable results in convalescent premature infants.

Female↗
PubMed1993

Metabolism of polysaccharides by the Streptococcus mutants dexB gene product.

The Streptococcus mutans dexB gene, a member of the multiple sugar metabolism (msm) operon, encodes an intracellular glucan 1,6-alpha-glucosidase which releases glucose from the non-reducing terminus of alpha-1,6-linked isomaltosaccharides and dextran. Comparison of primary amino acid sequences showed strong homology to Bacillus oligo-1,6-glucosidases and, like these enzymes, DexB was able to release free glucose from the alpha-1,4,6-branch point in panose. This suggested a role for DexB in the metabolism of either starch or intracellular polysaccharide, which contain such branch points. However, purified intracellular polysaccharide from the wild-type S. mutans strain LT11 and a mutant deficient in dexB revealed no substantial differences in the extent of branching as demonstrated by iodine staining spectra and the degree of polymerization. Furthermore, thin layer chromatography of radiolabelled intracellular polysaccharide digested with S. mutans wild-type and mutant cell extracts showed no differences in the products obtained. The involvement of DexB in dietary starch metabolism was investigated using alpha-limit dextrins produced from the action of alpha-amylase on starch. These induced the msm operon, including dexB, and the DexB enzyme was able to act on the alpha-limit dextrins to give further fermentable substrates. The transport system encoded by the msm operon can also transport alpha-limit dextrin. DexB may therefore be important in the metabolism of extracellular starch.

Amino Acid Sequence↗
PubMed1993

Cloning and expression of the multiple sugar metabolism (msm) operon of Streptococcus mutans in heterologous streptococcal hosts.

The multiple sugar metabolism (msm) operon of Streptococcus mutans is responsible for the uptake and metabolism of a variety of sugars. In order to further characterize the substrate specificities of the transport system, a 12-kb region of DNA containing the entire msm operon was cloned, via a novel two-step integration strategy, into the chromosomes of two heterologous streptococcal strains, Streptococcus gordonii Challis and Streptococcus anginosus Is57, as well as the chromosome of a natural isolate of S. mutans with a deletion of the msm region. These strains are unable to transport or ferment melibiose, raffinose, or isomaltosaccharides, but the newly constructed recombinants gained the ability to ferment all of these sugars. The S. gordonii Challis construct containing msm was shown to transport radiolabelled melibiose, raffinose, isomaltotriose, and isomaltotetraose, and the transport function was also subjected to induction by raffinose, an inducer of the msm operon in S. mutans. The results confirm the role of the msm operon in the transport and metabolism of melibiose, raffinose, and isomaltosaccharides.

Biological Transport↗
PubMed1993

Expression of gtfS is essential for normal insoluble glucan synthesis by Streptococcus downei.

The gtfI and gtfS genes of Streptococcus downei were investigated to determine the contribution of the respective enzymes to glucan production in the presence and absence of other glucosyltransferases. Extracts of Escherichia coli expressing cloned gtfS produced a short linear dextran from sucrose which could act as a primer for insoluble glucan synthesis when mixed with extracts of a strain expressing recombinant gtfI. To elucidate the contribution of gtfS to glucan production by S. downei, a mutant was constructed by insertionally inactivating gtfS. S. downei (gtfS mutant) colonies exhibited a marked phenotypic change on sucrose-containing media and a decreased ability to adhere to glass and produced no detectable water-insoluble glucan. These experiments confirm that expression of gtfS is essential for normal insoluble glucan synthesis by S. downei.

Gene Expression↗
PubMed1993

Multiple changes in cell wall antigens of isogenic mutants of Streptococcus mutans.

Isogenic mutants of Streptococcus mutans LT11, deficient in the production of the wall-associated protein antigens A and B, were generated by recombinant DNA technology. The hydrophobicity, adherence, and aggregation of the mutants were compared with those of the parent strain. These studies indicated that hydrophobicity, adherence, and saliva- or sucrose-induced aggregation were unaltered in the A- mutant but that hydrophobicity and adherence to saliva-coated hydroxylapatite were greatly reduced in the B- mutant whilst sucrose-dependent adherence and aggregation were increased. To determine whether these changes correlated with changes in the mutated gene product alone, the levels of a number of cell wall antigens were determined in each of the mutants. The loss of antigen A resulted in significantly reduced levels of wall-associated lipoteichoic acid, and loss of antigen B resulted in reductions in both antigen A and lipoteichoic acid. Data presented here thus suggest that changes in the expression of one wall antigen can have a dramatic effect on the levels of others.

Antigens, Bacterial↗
PubMed1993

MsmE, a lipoprotein involved in sugar transport in Streptococcus mutans.

Metabolic labelling by [14C]palmitic acid showed that growth of Streptococcus mutans LT11 in raffinose, an inducer of the msm operon, resulted in increased production of a 45-kDa lipoprotein corresponding to MsmE, which is believed to be a sugar-binding protein. MsmE was also labelled when an msmE clone was expressed in Escherichia coli. The presence of a lipid anchor on MsmE provides a likely explanation of how the sugar-binding protein component of the msm binding protein-dependent multiple sugar transport system is retained at the cell surface.

Amino Acid Sequence↗
PubMed1993

The isolation and characterization of milleri group streptococci from dental periapical abscesses.

Reports of the isolation of streptococci from dental abscesses have shown an association of the "S. milleri" group with such lesions. There has been considerable confusion regarding the taxonomy of these organisms, but the milleri group has recently been reclassified into three distinct species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. In this study, 45 samples from dental periapical abscesses were examined. Milleri group streptococci were isolated from 16 patients (37%), 15 being identified as S. anginosus and one as S. intermedius. In one patient, S. anginosus was isolated in pure culture, and it would appear that this is the predominant species of milleri group streptococci associated with periapical abscesses.

Adult↗
PubMed1993

Transport of sugars, including sucrose, by the msm transport system of Streptococcus mutans.

The range of substrates transported by the sugar-binding protein-dependent msm (multiple sugar metabolism) system of S. mutans was investigated. By determining the ability of unlabeled sugar to compete with radiolabeled melibiose transport, we have demonstrated that the transported sugars included a number of carbohydrates structurally related to raffinose. A model accommodating these results has been devised which accounts for the sugars transported by the msm transport system. Competition with radiolabeled melibiose transport indicated sucrose to be an msm substrate. This was confirmed by examination of uptake of radiolabeled sucrose in scrAB mutants lacking the sucrose-specific phosphotransferase system.

Biological Transport↗