Variation in the antibiotic producing bacterial flora of the human intestinal tract.

Various studies on the antagonistic activity of intestinal organisms have compared the antibacterial spectra of cultures isolated from large numbers of people (Halbert, 1948a; Gardner, 1950; Blackford et al., 1951; Cook et al., 1953). Little emphasis, however, has been placed on variation in antibiotic production by the organisms of a given person over a period of time. Halbert (1948b) reports fluctuation in antagonism against the infecting Shigella strain in a few children during the course of an outbreak of shigellosis in a mental hospital. Differences in the antibacterial spectra of the organisms isolated from the same person at different times were observed in preliminary studies in our laboratory (Szwed, 1954; Raad, 1956). An expansion of these studies was indicated in order to determine the permanence of antibiotic producing coliforms in the normal intestinal tract.