Biomedical subjects
Publications and source records attributed to B R Maier.
Calculated and chemically analyzed nutrient values for three weighed constant diets were dissimilar for calcium, magnesium, protein, and fat, and similar for fiber and ash. Fecal nutrient concentrations of ten healthy men fed the same constant diets were quite variable. Feeding constant weighed diets of similar composition does not assure the same fecal residue in the large colon of human subjects.
Ten human volunteers completed a 4-month diet series consisting of 1 month each of a control diet, a meatless diet, a high-beef diet, and the same control diet. Fat and fiber contents were essentially the same in all four diets, but protein content was doubled during the high-beef diet. During the 4th week on each diet, three stool specimens collected from each volunteer were analyzed for chemical composition and content of facultative, aerobic, and anaerobic bacteria. The bacteriological data are presented in this paper. High beef protein consumption had little effect on the composition of the intestinal flora. There were no significant differences in total counts of facultative and aerobic or anaerobic organisms in the feces when volunteers were on meatless or high-beef diets. At the species level, when counts during the two control diets were comparable, in only three instances did the change from the meatless to a high-beef diet significantly influence the bacterial numbers. The ratio of mean counts of anaerobic to facultative and aerobic organisms was approximately 15:1 during the meatless diet and 34:1 during the high-meat diet. The data indicate that animal protein consumption has little effect on the fecal bacterial profile in humans.
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Germfree mice were associated with selected species of human intestinal bacteria and then challenged with a streptomycin-resistant Shigella flexneri strain. Antagonism against Shigella was most pronounced in mice associated with Escherichia coli and least pronounced in mice associated with Bacteroides fragilis. A moderate degree of antagonism could be demonstrated in mice associated with either Streptococcus faecalis or Bifidobacterium adolescentis. Shigella persisted in the cecal contents of E. coli-associated mice at very low, stable levels. Shigella populations were reduced to levels below detection in the ceca of mice diassociated with E. coli and Bacteroides. Upon subsequent administration of streptomycin, Bacteroides disappeared from the ceca. The E. coli population was greatly reduced, and Shigella reappeared at very high population levels as an apparent recombinant which resembled E. coli biochemically. A streptomycin-resistant E. coli population subsequently emerged and became dominant in the ceca. Shigella concomitantly declined to levels below detection.
Five strains of Bacteroides fragilis isolated from human feces were assayed for their inhibitory activities against Shigella flexneri in vitro. Inhibition was not detected when Shigella and the Bacteroides strains were simultaneously inoculated into a defined liquid medium containing glucose. Inhibition was apparent only when Shigella was inoculated into established Bacteroides cultures. In exponential-phase cultures, the Shigella growth rate was diminished and logarithmic growth was prematurely interrupted. Shigella failed to multiply at all in stationary-phase Bacteroides cultures. An analysis of the stationary-phase cultures revealed that acetic and propionic acids were present in sufficiently high concentrations and the pH of the culture medium was sufficiently low to account for the inhibition of Shigella growth. In glucose-free Bacteroides cultures, Shigella multiplied almost as well as in control cultures, despite the presence of high concentrations of volatile fatty acids. At the high pH levels present in the glucose-free cultures, the acids were not toxic for Shigella. These results reaffirm the importance of the relationship between volatile fatty acids and pH in the inhibition of Shigella growth.