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Abstract
Development of the faecal flora of ex-germ-free BALB/c mice inoculated with faecal dilutions of two healthy human adults was examined. Although the numbers of Enterobacteriaceae in the developing flora were high, compared with those in the faeces used for inoculation, during the first 2 d, they decreased markedly from the third day. Conversely, anaerobic bacteria were present in low concentrations on day 1 and increased thereafter. On day 3, anaerobic bacteria which were dominant in the human faeces became dominant in the ex-germ-free mice. The development of the faecal flora of these mice resembled that of neonatal animals and humans. Interestingly, bifidobacteria were eliminated from the ex-germ-free mice inoculated with faeces from one of the donors within 2–8 wk, while other bacteria remained constant. The elimination of bifidobacteria seemed to be dependent on the composition of flora of the inoculated sample. Ex-germ-free mice with a Bifidobacterium-free human faecal flora may provide a suitable animal model for studying their role in human health.