Function of various intestinal bacteria in converting germfree mice to the normal state

Earlier work had shown that a collection of anaerobic bacteria, in conjunction with facultative anaerobes, may be implanted into germfree mice, thereby rendering the animals "normal" with respect to a variety of parameters tested. The present experiments indicate that a different collection of anaerobic bacteria, isolated from the cecum of normal mice, was necessary to convert germfree mice to the "normal" state when the animals were fed a crude diet, rather than the refined food which had been used in the earlier work. The nature and level of short-chain fatty acids associated with various natural or synthetic "normal" floras in the ceca of mice did not always correlate with the Escherichia coli population present, indicating that fatty acids were not the sole agents inhibiting bacterial populations in the intestine. Experiments are reported which indicate that intestinal anaerobes may under certain circumstances be sufficient to control the populations of other intestinal bacteria such as E. coli. In other instances, such as control of Shigella populations in the mouse intestine, intestinal anaerobes appeared to act synergistically with an E. coli strain, in spite of the fact that the population of the latter was itself suppressed by the anaerobes.