摘要：The human intestinal tract comprises a large variety of microorganisms, which create an ecosystem within the host that has a major effect upon host physiology and biology (1, 2). Recent years have shown an increase in studies regarding the influence of microorganisms on intestinal gene expression either in vivo, by colonizing germ-free mice with a defined microbiota (3), or in vitro by determining the interaction of bacteria with intestinal cell lines (4, 5). The impact of the gut microbiota on the host has been clearly demonstrated in model studies using Bacteroides thetaiotaomicron, a predominant gut commensal bacterium, the genome of which has been determined (6). When inoculated into germ-free mice, B. thetaiotaomicron could elicit the production of fucosylated glycans (Fucα1, 2Galβ-glycans) from the host via a molecular sensor FucR (7), and could also affect the expression of several mouse genes, and increase production of Ang4, an antimicrobial protein, which is involved in the host defence against pathogens (8). These examples all indicate that this commensal gut bacterium was able to interact with its host in a specific manner to affect formation of a particular ecosystem. Fermented dairy products, in particular, have long been used to improve the composition and activity of the intestinal microbiota. Such products do not appear to have any health risks. Probiotics, although very similar to starter cultures used in the fermentation of dairy products, are usually of a different origin and are intended to survive gastrointestinal (GI) transit (9). Probiotics have an established safety record and several strains have been used for long periods of time in diverse populations; therefore the safety of these strains seems to be well established and agreed (10). However, in order to be able to continue to provide safe versions, particularly of novel strains, an assessment of the intrinsic properties of probiotics is necessary. The intestine, and especially the colon, is heavily colonized by microbes. Translocation of these microorganisms to sites systemic to the gut poses a serious risk to the host. A number of diseases exist whereby this situation may occur. It would be of great benefit if probiotics could diminish this translocation and the severity of the ensuing disorder. The use of animal models is required to establish the safety and efficacy of new and existing probiotic strains for such applications (11, 12). Such models provide information on the effect of probiotics on translocation of members of the intestinal microbiota. Moreover, it has to be established that the used strain should not translocate either. The intestinal mucosa forms the border between the heavy colonized intestine and more sterile areas. It is therefore of primary importance to both the microbiota and host, and is a major target for probiotic safety and functionality. In this article, the results from three studies will be shown, dealing with safety-related properties of members of the intestinal microbiota and of probiotic bifidobacteria, and with the efficacy and safety of established and new probiotics in relation to bacterial translocation.
