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Biomedical subjects

I H Johnson

Publications and source records attributed to I H Johnson.

8 recordsLinked to original sources
PubMed1998

The prevalence of Helicobacter pylori in practising dental staff and dental students.

Recent studies suggest Helicobacter pylori is spread by faecal-oral or oral-oral transmission. Gastroenterologists who are exposed to gastric secretions and saliva have a high prevalence of H. pylori infection. Venous blood was obtained from 92 dentists, 40 dental nurses, 33 fifth year and 30 first year dental students. An ELISA assay was used to detect H. pylori IgG antibodies. Results were compared with an age and sex matched normal population. The prevalence of H. pylori infection in dentists, dental nurses, fifth year dental students and first year dental students were 23 per cent, 18 per cent, 18 per cent and 16 per cent, respectively. There were no significant differences when compared with the normal population controls. The prevalence of H. pylori antibody was not significantly increased with years of practice or patient contact time in dentists and dental nurses. Helicobacter pylori infection is uncommon in dental professionals working in the oral cavity.

Adolescent↗
PubMed1995

Anticariogenicity of calcium phosphate complexes of tryptic casein phosphopeptides in the rat.

Casein phosphopeptides (CPP) stabilize calcium phosphate through the formation of casein-phosphopeptide amorphous calcium-phosphate complexes (CPP-CP). The ability of CPP-CP to reduce caries activity was investigated by use of specific-pathogen-free rats inoculated with Streptococcus sobrinus. The animals consumed a defined cariogenic diet free of dairy products. Solutions (100 microL) of the CPP-CP (0.1, 0.2, 0.5, 1.0% w/v) were applied to the animals' molar teeth twice daily. Other groups of animals received solutions containing 500 ppm F, the non-phosphorylated peptides of a casein tryptic digest (0.5% w/v), or the calcium-phosphate complex of a synthetic octapeptide, Ac-Glu-Ser(P)-Ile-Ser(P)-Ser(P)-Ser(P)-Glu-Glu-NHMe, corresponding to the common sequence in the CPP. The CPP-CP significantly reduced caries activity in a dose-response fashion, with 1.0% CPP-CP producing 55% and 46% reductions in smooth surface and fissure caries activity, respectively, being similar to that of 500 ppm F. The anticariogenic effects of CPP-CP and fluoride were additive, since animals receiving 0.5% CPP-CP plus 500 ppm F had significantly lower caries activity than those animals receiving either CPP-CP or fluoride alone. The tryptic digest of casein with the phosphopeptides selectively removed showed no anticariogenic activity. The synthetic octapeptide-calcium phosphate complex significantly reduced caries activity, confirming that this calcium-phosphate-stabilizing portion of the casein phospho-peptides is associated with anticariogenicity. The CPP-CP did not significantly affect the level of S. sobrinus in fissure plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Extracellular dextranase from Streptococcus oralis.

A human dental plaque organism, Streptococcus oralis (S. mitior), was cultivated in a dextran-free, dialysed medium, and dextranase activity was isolated from the cell-free, culture supernatant. The lyophilized, crude enzyme preparation, optimum pH 6, was subjected sequentially to anion exchange and gel filtration fast protein liquid chromatography (FPLC). The dextranolytic fraction from gel filtration FPLC produced a symmetrical, baseline resolved peak. The dextranolytic enzyme was purified 1,126-fold with a yield of 2.4%. Amino acid analysis revealed a large proportion of alanine and an abundance of acidic amino acids. This extracellular enzyme isolated from S. oralis is constitutive and has a relative molecular mass of 45 kD. Further investigation of the possible structural and biochemical effects of endogenous bacterial glucanases in human dental plaques is necessary.

Amino Acids↗
PubMed1991

Dextranase activity of streptococcal isolates from human dental plaques.

Streptococci were isolated from sixty human dental plaques. Of those isolates which exhibited dextranolytic activity on culture media containing dextran, three were selected for further investigation. Two of these isolates were identified as Streptococcus mitior and the other was a strain of Streptococcus mutans. The organisms were cultivated in a dialysed medium and enzyme activities isolated from culture supernatants by precipitation with ammonium sulphate, dialysis and lyophilization. Decolourized annuli surrounding wells in agar plates containing Blue Dextran 2000 provided evidence of dextranase activity present in culture supernatants, precipitated and redissolved proteins, dialysis retentates and lyophilized materials. The pH optima for the crude enzyme preparations were determined using the modified assay of Koh and Khouw (1970). Dextranases from the Streptococcus mitior isolates had optima at pH 6, and the optimal activity for the enzyme from the Streptococcus mutans isolate occurred at pH 5.5. Additional studies of the purified enzymes are necessary to increase understanding of the possible effects of these enzymes in human dental plaques.

Dental Plaque↗
PubMed1990

Glucanase-producing organisms in human dental plaques.

Selective media were used to isolate a wide range of bacteria from sixty human dental plaques. Glucanase activities of the isolates were determined on dextran- and starch-containing media. All sixty samples of dental plaque yielded some colonies showing amylolytic and dextranolytic activities. The glucanase-producing organisms comprised 20% of the isolates. Of these 38% were Gram-positive rods, 27% Gram-positive cocci, 28% Gram-negative rods and 7% were Gram-negative cocci. The cultural groups most commonly represented among the glucanase-producing isolates were Actinomycetaceae, streptococci, haemophili and Gram-negative anaerobes. Species prominent among these isolates included Streptococcus sanguis, Streptococcus mitior, Actinomyces naeslundii, Actinomyces viscosus, Bacterionema matruchotii, Bifidobacterium sp. and Bacteroides sp. No isolates capable of degrading starch or dextran were identified as Streptococcus milleri, Rothia dentocariosa or Fusobacterium sp. This study has shown that a wide range of bacterial species commonly isolated from human dental plaques exhibit both amylolytic and dextranolytic activities. In order to understand glucan metabolism in human dental plaques further investigation of these catabolic activities is necessary.

Bacteria↗