Continuous culture of human faecal bacteria as an in vitro model for the colonic microflora

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To investigate the role of human gut bacteria in the metabolism of potentially reactive compounds we have developed an in vitro model of the human faecal microflora using a two-stage continuous culture inoculated with human faeces. The cultured bacterial population retained many of the bacteriological and biochemical characteristics of the flora present in the faecal sample used for inoculation. Obligate anaerobes were the predominant bacterial types found in vitro and included Bacteroides ovatus and Bifidobacterium adolescentis. A comparison of in vivo (faeces) and in vitro bacterial enzyme activities that are known to be involved in the biotransformation of potentially toxic compounds found the activities of hydrolytic enzymes to be similar but reductive enzymes exhibited higher activities in the continuous culture model. When substrates of the enzymes were added to the culture vessel, the enzymes were induced to varying extents. The short-chain fatty acid profile in the culture was almost identical to that in faeces with the order of abundance being the same in two systems. These results indicate that the continuous culture of faecal bacteria can provide a suitable model for studying bacterial interactions and biotransformation of the human colonic flora.