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Biomedical subjects

K W Knox

Publications and source records attributed to K W Knox.

At least 37 records · Page 2Linked to original sources
PubMed1993

The aggregation of human platelets by Lactobacillus species.

The ability to aggregate human platelets was examined for five Lactobacillus rhamnosus strains and five Lactobacillus paracasei subsp. paracasei strains isolated from patients with infective endocarditis (IE), 25 laboratory isolates from the same two species, and 14 strains from five other oral species, namely Lactobacillus acidophilus, Lactobacillus fermentum, Lactobacillus oris, Lactobacillus plantarum and Lactobacillus salivarius. Amongst the L. rhamnosus strains, platelets were aggregated by all five IE strains and 8/16 laboratory strains. For the L. paracasei subsp. paracasei strains, the respective numbers were 2/5 and 2/9. Aggregation also occurred with 11/14 strains of the other five species; each species was represented. The optimal ratio of bacteria to platelets for aggregation was approximately 1:1, and there was considerable variation in the lag phase that preceded aggregation, depending on the source of the platelets. Overall, the lag phase varied between 0.25 +/- 0.1 and 20.4 +/- 3.2 min and the percentage aggregation ranged between 70 +/- 2.6 and 104 +/- 13.5%. Confirmation that aggregation was being observed came from studies with five strains on the inhibitory effects of EDTA, dipyridamole, apyrase, imipramine, acetylsalicylic acid and quinacrine. Inhibition of aggregation by L. rhamnosus strains by the peptide arginine-glycine-aspartic acid-serine (RGDS) further indicated a role for fibronectin and/or fibrinogen. Pronase treatment of cells for 1 h and extraction of bacterial surface components with 0.1 M-Tris/HCl (pH 8.5) at 37 degrees C for 1 h stopped aggregation in 8/9 IE strains. Extracted surface proteins (200 micrograms) completely inhibited platelet aggregation by 8/9 of the homologous strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteremia↗
PubMed1993

Biochemical properties of Streptococcus sobrinus reisolates from the gastrointestinal tract of a gnotobiotic rat.

Streptococcus sobrinus strain 6715-13-201 was inoculated into the oral cavity of a gnotobiotic rat and then reisolated from different portions of the gastrointestinal tract. Fourteen isolates, selected on the basis of their colonial morphology, were then screened for their ability to adhere to saliva-coated hydroxyapatite (SHA) in vitro, and their ability to produce extracellular polysaccharide from sucrose, and low pH in glucose broth. Certain isolates were also tested for their cariogenic potential as monoinfectants in gnotobiotic rats. All isolates differed in their abilities to adhere to SHA, with most showing an increased level of adhesion in the presence of sucrose, but this did not correlate with their ability to be aggregated by dextran. Most isolates were capable of producing glucosyltransferases (with only one exception) and dextranases (also one exception). There was more variability in the production of dextranase inhibitor. No isolate was capable of producing dextranase inhibitor in the absence of dextranase production. There were no correlations between the ability of isolates to adhere in vitro or produce/utilize polysaccharides and their ability to produce caries in vivo. Due to the differences between strains in their abilities to adhere, produce polysaccharides, utilize polysaccharides or produce a low pH and the lack of correlation between any of these parameters and cariogenicity, the results suggest that the ability of strains to colonize and produce caries depends on a number of different characteristics, no one of which is essential.

Animals↗
PubMed1993

Coaggregation of oral lactobacilli with streptococci from the oral cavity.

The ability of oral lactobacilli to coaggregate with streptococci and actinomycetes was investigated. Of the 7 species of lactobacilli studied, only two were capable of coaggregation and the coaggregation was restricted to streptococci. Lactobacillus salivarius strains (2/4) coaggregated with Streptococcus salivarius, Streptococcus gordonii, Streptococcus crista and tufted Streptococcus sanguis II strains. Lactobacillus fermentum (2/3) coaggregated with S. gordonii and S. sanguis. The coaggregation between L. salivarius and S. salivarius, S. gordonii or tufted S. sanguis II strains was mediated by a protein on the surface of the lactobacilli and was not inhibited by lactose. The coaggregation between L. fermentum and the streptococci was mediated by protein on the surface of the streptococci and was inhibited by lactose.

Actinomyces↗
PubMed1991

An examination of strains of the bacterium Streptococcus vestibularis for relative cariogenicity in gnotobiotic rats and adhesion in vitro.

The cariogenicity and adhesion of six strains of Streptococcus vestibularis were compared with those of strains of Strep. salivarius. All strains of Strep. vestibularis produced low levels of caries, confined to the fissures, whereas the two strains of Strep. salivarius produced high levels of caries, with one strain producing approximal as well as fissure caries. The values for adhesion to saliva-coated hydroxyapatite of Strep. vestibularis in the absence (median 4.74%) and the presence (median 4.67%) of sucrose were not statistically different, nor did they differ significantly from those of Strep. salivarius. Strains of Strep. vestibularis were able to adhere to buccal epithelial cells (median 1.19%) as well as could Strep. salivarius strain HB (1.65%). Neither sucrose nor saliva greatly aggregated the strains of either species. Strep. vestibularis did not adhere to hexadecane (median 18.5%) to the same extent as did Strep. salivarius strains (median 69%). There was a significant correlation between the adhesion in the presence and absence of sucrose (p less than 0.01). Strep. vestibularis strains could not coaggregate with either actinomycetes or Veillonella spp. whereas Strep. salivarius strains were able to coaggregate with Veillonella spp.

Actinomyces↗
PubMed1991

The role of oral bacteria in the pathogenesis of infective endocarditis.

Various micro-organisms have been implicated as causative agents for bacterial endocarditis, including lactobacilli and in particular the viridans streptococci which are more commonly associated with dental caries. Of these, the most frequently isolated one has the descriptive name Streptococcus sanguis. The disease is characterized by growth of micro-organisms within a platelet-fibrin thrombus protruding from a valve leaflet. An understanding of the pathogenesis involves knowledge of the mechanisms of conversion of the normal vascular surface to a thrombogenic one and the adhesion of micro-organisms to such surfaces. Model systems to study this interaction include experimental animals, mammalian epithelial cells and platelets, and proteins such as fibronectin and fibrinogen. Microbial protein surface components (adhesins) and lipoteichoic acid have also been implicated. Capsular polysaccharides may be involved, but the role of dextrans formed from sucrose has been over-emphasized as the polymers are not formed in situ. Antibiotic prophylaxis for patients at risk is based on bacteriostatic or bactericidal action. However, bacterial cell surface components involved in adhesion may also be affected, and knowledge of such reactions could provide a more rational basis for antibiotic prophylaxis.

Bacterial Physiological Phenomena↗
PubMed1991

Enumeration of oral streptococci on media containing different concentrations of sodium and potassium ions.

Laboratory "type" strains of oral streptococci were screened for their ability to grow on mitis-salivarius agar (MSA) in the presence of increasing concentrations of either Na+ or K+ up to 500 mmol/L. Strains were generally better able to withstand increasing concentrations of Na+ than K+, although low numbers of colony-forming units (cfus) were seen with the highest concentration of either cation. Two strains of Streptococcus mutans, Ingbritt 162 and Ingbritt 175, behaved differently when the concentration of cation was increased from 50 to 200 mmol/L; the latter showed a marked increase in the number of cfus when the Na+ concentration was increased from 50 to 200 mmol/L, whereas there was a decrease with strain Ingbritt 162. Strains of oral streptococci from the saliva of adults and children were isolated on modified MSA containing known concentrations of Na+ and K+ and further examined if they showed "mutans-like" colony morphology. The number of cfus generally dropped as the concentration of Na+ or K+ was increased from 200 to 350 or 500 mmol/L. Greater numbers of streptococci were tolerant to Na+ than to K+. Half of the isolates were members of the Streptococcus sanguis group (SSG), either Streptococcus mitis or S. sanguis II, and these were more tolerant to high concentrations of Na+ or K+ than other isolates that were identified as Streptococcus morbillorum, Streptococcus acidominimus, and Streptococcus milleri.

Adult↗
PubMed1990

Surface-associated properties of Streptococcus milleri group strains and their potential relation to pathogenesis.

Thirty strains from the Streptococcus milleri (anginosus) group (SMG) obtained from various sources were tested for a range of characters that could be associated with pathogenicity and the results were compared with those for type strains of S. sanguis, S. mutans and S. pyogenes. The SMG strains were heterogeneous in all tests. Most (18) belonged to one of the Lancefield groups with group F predominating. Adherence of strains isolated from abscesses to buccal epithelial cells was greater than that of other strains (p = 0.033). Compared with strains of S. sanguis, SMG strains were generally not aggregated by human saliva. They differed from the type strain of S. pyogenes in their relative ability to bind fibrinogen and fibronectin; they were less effective in binding fibrinogen (0.33-4.28% cf. 22% for S. pyogenes) and generally more effective in binding fibronectin (0.49-12.37% cf. 0.95%). Strains isolated from infections were statistically better at binding fibronectin than other strains (p less than 0.001). The ability of strains to adhere to saliva-coated hydroxyapatite (SHA) varied 10-fold, from 0.16-16.35%. The amount of fibronectin bound by SMG strains correlated with their ability to adhere to SHA (p less than 0.001). The hydrophobicity of the strains, as measured in the hexadecane partition assay, ranged from 0.0% to 99.0%. Some strains carried both positive and negative cell-surface charges and some strains with a highly hydrophobic cell surface also possessed a relatively high cell-surface charge. A minority of strains possessed a net positive cell-surface charge. Neither hydrophobicity nor cell-surface charge was related to the capacity of strains to adhere to SHA. Strains of SMG co-aggregated weakly with strains of Veillonella parvula, V. dispar, Actinomyces viscosus and A. naeslundii.

Bacterial Adhesion↗
PubMed1986

Comparison of extracellular protein profiles of seven serotypes of mutans streptococci grown under controlled conditions.

Extracellular proteins produced by the four human commensal species of mutans streptococci were analysed. The organisms used were Streptococcus mutans, serotypes c, e and f, Streptococcus cricetus, serotype a, Streptococcus rattus, serotype b, and Streptococcus sobrinus, serotypes d and g. They were grown in continuous culture at different generation times and pH values in media containing either glucose or fructose to determine the extent of variation in extracellular protein production that could occur for an individual strain. The results for different organisms grown under the same conditions were then compared. The total amount of protein of molecular mass greater than or equal to 60 kDa varied considerably with the growth conditions and with the strain. Generally more protein was present at a higher pH, conditions under which the organisms also form more lipoteichoic acid. With respect to individual protein components SDS-PAGE proved better than isoelectric focusing for detecting phenotypic responses by a particular strain to environmental changes and differences between the different strains. Differences in the molecular masses of protein components were particularly pronounced in the regions designated P1 (185-200 kDa), P2 (130-155 kDa) and P3 (60-95 kDa). Every strain produced at least one component in the P1 region that cross-reacted with antiserum to the purified protein from S. mutans serotype c, a protein which is indistinguishable from antigens B and I/II. Two components in the P2 region were dominant in the case of S. cricetus and S. sobrinus strains and showed glucosyltransferase (GTF) activity. GTF activity was also detected in the P3 region, particularly with S. mutans strains.

Bacterial Proteins↗
PubMed1986

Comparative studies on the protein profiles and hydrophobicity of strains of Streptococcus mutans serotype c.

Twelve strains of Streptococcus mutans serotype c were grown in batch culture with glucose at constant pH (6.0) and a number of properties compared. On the basis of their cellular and extracellular protein profiles, the strains were divided into three groups, I, II and III, containing five, four and three strains, respectively. The extracellular protein profiles for a particular strain differed if the organisms were grown either at pH 6.0 with fructose instead of glucose or with glucose but without pH control. The total amount of extracellular protein produced by group III strains grown in glucose-containing medium at pH 6.0 was several times that produced by strains of groups I and II, which were also more hydrophobic. One of the potentially important proteins is P1, also called antigen B or I/II, and it was shown to be entirely in the culture fluid of group III strains but mostly cell-associated from strains of groups I and II. Approximately half of the cell-associated fraction of P1 could be removed with hot sodium dodecyl sulphate.

Bacterial Proteins↗
PubMed1986

Critical micelle concentrations of lipoteichoic acids.

Purified lipoteichoic acids (LTAs) from several gram-positive organisms have been shown, by methods involving spectral changes of an added merocyanine dye probe, to have critical micelle concentrations in the range of 1 to 10 micrograms/ml, suggesting that acylated LTAs in their monomer forms may represent the major configuration of extracellular LTAs in bacterial culture fluids. The critical micelle concentrations obtained did not differ markedly with degree of carbohydrate substitution of the polymers. The significance of these findings in relation to the biological properties of LTA is discussed.

Acridine Orange↗
PubMed1985

Current concepts in periodontal diseases.

Periodontal diseases are common oral diseases that afflict all humans to some degree. The major aetiological agent is dental plaque--the complex microflora which forms on teeth in the absence of effective oral hygiene. The interaction of the microbial flora and the periodontal tissues produces an inflammatory response and tissue breakdown. Recent information has categorized periodontal diseases on the basis of increased knowledge about the particular microorganisms associated with the different clinical conditions. In addition, the important role of host defences, in particular the phagocytic cellular elements, has allowed for a better understanding of the pathological processes. This knowledge is contributing towards the development of rational and effective therapy for all forms of periodontal diseases. Because of the widespread occurrence of periodontal diseases and their potential relationships to systemic conditions, it is important that medical practitioners should be able to recognize, and be conversant with methods of treatment of, these diseases.

Acute Disease↗
PubMed1985

Comparative studies on the effect of growth conditions on adhesion, hydrophobicity, and extracellular protein profile of Streptococcus sanguis G9B.

Streptococcus sanguis G9B was grown in continuous culture at different generation times and pH values in media containing either glucose or fructose and differing in the concentrations of Na+ and K+. The growth pH, carbohydrate, and cation concentration each affected the yield of organisms, their ability to adhere to saliva-coated hydroxyapatite beads, and their hydrophobicity, as measured by adhesion to hexadecane. There was no correlation between adhesion to saliva-coated hydroxyapatite beads and hydrophobicity, the values for hydrophobicity varying between 44 and 83% for organisms that adhered poorly and between 24 and 75% for those that adhered effectively. For organisms grown in batch culture at pH 6.0 or 7.0 there was similarly no correlation between adhesion and hydrophobicity. The growth conditions also had a considerable influence on the production of extracellular protein. The total amount was greater at pH 7.5 than at other pH values, and there were also differences in the individual components in response to changes in generation time, pH, carbohydrate source, and cation concentration. Two protein bands were identified, namely, glucosyltransferase and protein P1 (also called antigen B or I/II). However, there was no correlation between a particular protein component and adhesion.

Bacterial Proteins↗
PubMed1984

Characterization of polysaccharide antigens of Streptococcus mutans B13 grown under various conditions.

Bacteria may respond to changes in their environment by varying the synthesis of surface components. This study examined the effects of various culture conditions on two wall polysaccharides of Streptococcus mutans B13 (serotype d): serotype d antigen, a galactose-glucose polymer, and RGP antigen, a rhamnose-glucose polymer. Cells were grown in a chemostat at various dilution rates (D) and pH values, including D = 0.05, 0.1, and 0.5 h-1 at pH 6.0 and D = 0.1 h-1 at pH 5.5, 6.0, 6.5, and 7.5. The cells were examined for protein and carbohydrate content by colorimetric assays and gas-liquid chromatography. Rantz-Randall extracts (120 degrees C, 30 min) and M-1 N-acetylmuramidase digests were prepared and examined for the presence of specific antigens by agar gel diffusion and quantitative precipitation assays. Cell preparations did not vary significantly with respect to total protein or carbohydrate content; however, cells grown at D = 0.1 h-1 and pH 7.5 had a significantly higher rhamnose content than did the other preparations. Rapidly growing cultures appeared to be more resistant to M-1 N-acetylmuramidase digestion than did slower-growing cultures. Agar gel diffusion studies demonstrated that both serotype d and RGP antigens were present in all samples, although significantly less RGP antigen was noted in the pH 7.5 culture. These observations were confirmed by quantitative precipitation assays. M-1 N-acetylmuramidase digests of the pH 7.5 culture were lacking in RGP precipitation activity although RGP inhibition activity was demonstrated. The data suggest that the cell content of serotype d antigen was relatively constant under the growth conditions tested, whereas the synthesis of RGP antigen was modified under conditions of high pH.

Antigens, Bacterial↗
PubMed1983

Characteristics of a high molecular weight extracellular protein of Streptococcus mutans.

A high molecular weight protein antigen, designated P1, has been isolated from the culture fluid of chemostat-grown Streptococcus mutans strain Ingbritt and shown to be free of other antigens including glucosyltransferase. Antiserum against the protein was used in rocket immunoelectrophoresis to confirm and extend the previous observation that there were major differences in the amount of the protein produced under different growth conditions. Physico-chemical and serological studies indicated that protein P1 was indistinguishable from antigens B, I/II and IF isolated in other laboratories. Mammalian tissue cross-reactivity of protein P1 was demonstrated by binding of antiserum to P1 to sections of normal rabbit tissues, particularly heart. There was also a statistically significant increase in the number of mononuclear leucocytes in heart tissue of rabbits which had been injected with protein P1, when compared with the levels in control uninjected rabbits; injection with whole cells of S. mutans Ingbritt did not produce this effect.

Amino Acids↗
PubMed1983

Influence of growth conditions on adherence of Streptococcus mutans ingbritt to saliva-coated hydroxyapatite.

Streptococcus mutans Ingbritt grown under standardized conditions adhered less effectively to saliva-coated hydroxyapatite beads than did Streptococcus sanguis G9B, and there was competition for binding. The results with Ingbritt were influenced by the generation time, the pH of growth, and the carbohydrate source as shown by studies on organisms grown in continuous culture.

Adsorption↗