ANALYSIS OF FECAL POPULATIONS OF BIFIDOBACTERIA AND LACTOBACILLI AND INVESTIGATION OF THE IMMUNOLOGICAL RESPONSES OF THEIR HUMAN HOSTS TO THE PREDOMINANT STRAINS

The bifidobacterial and lactobacillus populations of fecal samples col lected from 10 human subjects were studied. The numbers of bifidobacte ria were similar in the fecal samples of all of the subjects, but lact obacillus numbers varied, even between samples collected from the same individual. Analysis of the composition of the bacterial populations by ribotyping and pulsed-field gel electrophoresis to differentiate be tween strains showed that, at least for the numerically predominant st rains, each subject harbored a unique collection of bifidobacteria and lactobacilli. Predominant bifidobacterial and lactobacillus strains d etected in the feces of each subject were used in immunological assays (lymphocyte transformation, serum antibody titers) to determine the i nfluence of the bacteria on the immune system of their host. Immunoglo bulin G antibodies reactive with lactobacilli were detected at high co ncentrations; antibodies reactive with bifidobacteria were present at lower concentrations. The antibodies appeared to be genus specific rat her than strain specific. The results of the study emphasized the comp lexity of the relationship that exists between the intestinal microflo ra and the human host.