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M Shivers

Publications and source records attributed to M Shivers.

5 recordsLinked to original sources
PubMed1988

Interaction between wild-type, mutant and revertant forms of the bacterium Streptococcus sanguis and the bacterium Actinobacillus actinomycetemcomitans in vitro and in the gnotobiotic rat.

In vitro, Streptococcus sanguis inhibits the growth of Actinobacillus actinomycetemcomitans, a presumed aetiological agent of localized juvenile periodontitis. When provided with glucose and good aeration, a growing culture of Strep. sanguis was found to produce hydrogen peroxide at concentrations in excess of the maximum LD50 reported for strains of A. actinomycetemcomitans. This concentration of hydrogen peroxide also inhibits the growth of the producer organism. A mutant of Strep. sanguis was isolated that lacked the ability to produce alpha-haemolysis on blood agar. This mutant had less than 3 per cent of its parent's level of pyruvate-oxidase activity, and made no detectable hydrogen peroxide. In vitro, the mutant had also lost the ability to inhibit the growth of A. actinomycetemcomitans. A spontaneous revertant, isolated by its ability to produce alpha-haemolysis, was found to have regained parental levels of pyruvate-oxidase activity and hydrogen-peroxide production and could inhibit the growth of A. actinomycetemcomitans in vitro. A gnotobiotic rat model was used to demonstrate that Strep. sanguis and A. actinomycetemcomitans interact in vivo and that this interaction depends on hydrogen-peroxide production by Strep. sanguis.

Actinobacillus↗
PubMed1985

The relationships between streptococcal species and periodontopathic bacteria in human dental plaque.

The existence of antagonistic and commensal relationships between microorganisms was investigated. The predominant cultivable flora in 172 plaque samples from active and non-active sites in 32 human subjects with destructive periodontitis was determined. The presence of putative periodontopathic organisms (Bacteroides gingivalis, Bacteroides intermedius, Bacteroides forsythus, Wolinella recta, Actinobacillus actinomycetemcomitans, and Eikenella corrodens) in a site was correlated with the absence of certain viridans streptococci (Streptococcus sanguis, Streptococcus uberis and Streptococcus intermedius), and vice versa. A strong commensal relationship was found between B. gingivalis and Strep. intermedius. The second study involved 3 subjects with intractable periodontitis whose plaque harboured large numbers of one or more of these periodontopathic organisms. This plaque contained fewer organisms capable of inhibiting the growth of the periodontopathic strains in vitro when compared with a clinically-healthy control subject. Intermediate levels of inhibitors were found in plaque taken from non-active lesions. The majority of inhibitors in plaque from the healthy control were viridans streptococci. Hydrogen-peroxide production by these organisms appears to be the principal mechanism of growth inhibition for periodontopathic organisms. Bacterial interactions may thus be causally related to both periodontal health and disease.

Actinobacillus↗
PubMed1979

Studies on the tissue specificity of a circulating renotropic factor.

In 1970, it was found that sera removed from rats 24 hr after unilateral nephrectomy stimulate the incorporation of 3H-Thymidine into the DNA of incubating rat renal cortex. The same sera did not influence isotope incorporation into the DNA of incubating liver, spleen, and lung tissue. Later, a substance was described in renal tissue that enhanced the action of the renotropic factor in sera. It was proposed that this tissue factor activated the circulating renotropic substance and that lack of this activator in other tissues was responsible for the specificity of the circulating renotropic substance to renal tissue. The present study suggests that this is the case as the addition of the renal tissue factor and sera from uninephrectomized rats can stimulate 3H-Thymidine incorporation into the DNA of rat liver slices.

Animals↗
PubMedDate not supplied

Further studies on a renotropic system in rats.

Based upon many investigations, the existence of short-lived, specific, circulating substances which incite and/or regulate compensatory renal growth has been proposed. In our studies, we find that sera and plasma from unilaterally nephrectomized rats compared to sera and plasma from sham-operated rats stimulate the incorporation of (3)H-thymidine monophosphate, (3)H-thymidine and (14)C-uridine into the DNA of incubating rat kidney fragments. While extracts from growing rat kidneys are not excitatory, they produce a relative enhancement to incorporation of isotope into DNA when combined with sera from uninephrectomized rats-more than the sera do alone. The above is found also for the incorporation of (14)C-uridine into RNA of incubating rat kidney fragments. Sera from uninephrectomized rats fail to stimulate DNA synthesis in liver slices from rats but do so in the presence of extracts from growing kidneys. Renotropic factors in sera and extracts do not appear to work by diluting the isotopes, by enhancing transport, or by effecting overall metabolism of the renal cells. The above described serum and liver factors may play a role in compensatory renal growth.

Animals↗