Composition and ecology of the human intestinal flora.

Longitudinal quantitative cultures of fecal flora of 20 newborns, 4 older babies and 10 healthy adults were carried out to study the composition and development of the intestinal flora. In all newborns the same sequence of colonization was observed. The numbers of aerobic and anaerobic bacteria fluctuated and reached finally numbers of 10(10)/g wet weight. In adults the flora was in balance with 10(5)-10(7) aerobic and 10(10)-10(11) anaerobic bacteria/g wet weight. Interaction experiments in vitro showed growth inhibition of Bacteroides fragilis by all intestinal species isolated. Bifidobacteria were not inhibited. The assumption was made that this type of interaction could be one of the mechanisms involved in the intestinal micro-ecology. Three of the Bacteroides fragilis strains tested were able to grow on "natural intestinal substrates" as gastric mucin, glycogen and a variety of plant polysaccharides. Acetic, lactic, propionic and succinic acids were detected as fermentation products.

Iron requirement and chelator production of staphylococci, Streptococcus faecalis and enterobacteriaceae.

The effect of iron deprivation on growth of 101 aerobic strains of gram-positive and gram-negative bacteria was studied on agar media in the presence of various concentrations of the synthetic iron chelator ethylene diamine diorthohydroxyphenyl acetic acid (EDDA) and the iron binding protein transferrin. Growth of Staphylococcus epidermidis was inhibited by 15 mM EDDA and 1.5 mM transferrin. Staphylococcus aureus was only inhibited by 44 mM EDDA and not by transferrin. None of the strains of S. faecalis was inhibited. The majority of the enterobacteriaceae (E. coli, Salmonella spp, Klebsiella spp) was inhibited by 44 mM EDDA and 1.5 mM transferrin. The relation between susceptibility and concentration of EDDA and transferrin was expressed as S-value for each species. Iron supply with various iron compounds could restore the effects of inhibition. In all species except in S. faecalis iron chelator production could be demonstrated, using indicator plates of media containing EDDA and flooded with 10(4)--10(5) colony forming units of indicator organisms. The iron chelator of both S. epidermidis and S. aureus could stimulate growth of S. epidermidis, but not that of enterobacteriaceae. Iron chelators from all gram-negative bacteria were functionally interchangeable, but did not stimulate growth of gram-positive bacteria.