Microbial Competition in Reactors with Wall Attachment: A Comparison of Chemostat and Plug Flow Models

The indigenous microflora of the human large intestine is a complex ecosystem consisting of several hundred species of microorganisms [5]. The composition of the microflora is remarkably stable; the species coexist without one or a few becoming dominant [12]. One of its most important contributions to the host is its ability to impede the colonization of the intestinal tract by nonindigenous microorganisms [19]. The term “colonization resistance” [22] is used to describe all mechanisms involved in this function. An understanding of these mechanisms would represent a major contribution to human health. Competition for nutrients and competition for adhesion sites appear to be widely accepted as among the most important components of colonization resistance [4, 12, 13, 14, 19, 20]. The difficulties associated with in vivo studies of the human intestinal microflora are self-evident. A number of in vitro models of bacterial interactions in the gut have been proposed by various authors. Rolfe [19] states that the chemostat, or continuous-stirred tank reactor (CSTR), is likely the best system for the study of bacterial interactions, since complex population levels of several different organisms can be maintained. Freter and his