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Category: Clinical Microbiology; Bacterial Pathogenesis
Interactions of the Commensal Flora with the Human Gastrointestinal Tract, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817619/9781555813239_Chap13-1.gif /docserver/preview/fulltext/10.1128/9781555817619/9781555813239_Chap13-2.gifAbstract:
This chapter surveys recent information on the roles of the commensal intestinal flora and provides an overview of how the natural symbiosis can be enhanced. The dominant microbial genera of the human gastrointestinal tract include Bacteroides, Bifidobacterium, Eubacterium, Lactobacillus, Clostridium, Fusobacterium, Peptococcus, Peptostreptococcus, Escherichia, and Veillonella. The ability of the commensal flora to persist in the intestinal lumen stands in stark contrast to the abundance and vigor of the intestinal immune system. The intestinal mucosa must maintain a highly selective barrier function, capable of permitting the absorption of highly variable nutrients and the sampling of antigens while excluding pathogenic microorganisms. Just as the presence of the commensal flora is needed to drive the maturation of the immune system, several studies have suggested that the flora is required to establish normal epithelial barrier function. The studies by Gordon and Hooper have illuminated dramatically the contributions of the commensal flora to ontogeny of the intestinal mucosa. The study of health-promoting effects conferred by administration of a live commensal flora, so called probiotic species, has a long but often confusing history. The contribution of the enteric commensal flora to human health is only beginning to be appreciated, and many more studies are required. The availability of molecular approaches will greatly accelerate laboratory investigations, but careful clinical observations are required to ascertain the full scope of these effects.
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Effects of coculture and preconditioned media on the expression of the global regulator of enteroaggregative E. coli virulence, AggR. Enteroaggregative E. coli strain 042 was cocultivated individually with various enteric bacteria in Luria broth at 37°C to the late log phase. Conditioned media were prepared by cultivating the enteric species, filtering out bacterial growth, and correcting pH and nutrient concentration. The aggR transcript in both experiments was quantitated by real-time reverse transcription-PCR. Values expressed are the number of aggR transcripts in coculture or preconditioned media compared with aggR expression in pure control cultures of 042. aggR expression is enhanced by Enterococcus and Clostridium species and diminished by Lactobacillus and Veillonella species. Reprinted from reference 63 with permission.
Effects of coculture and preconditioned media on the expression of the global regulator of enteroaggregative E. coli virulence, AggR. Enteroaggregative E. coli strain 042 was cocultivated individually with various enteric bacteria in Luria broth at 37°C to the late log phase. Conditioned media were prepared by cultivating the enteric species, filtering out bacterial growth, and correcting pH and nutrient concentration. The aggR transcript in both experiments was quantitated by real-time reverse transcription-PCR. Values expressed are the number of aggR transcripts in coculture or preconditioned media compared with aggR expression in pure control cultures of 042. aggR expression is enhanced by Enterococcus and Clostridium species and diminished by Lactobacillus and Veillonella species. Reprinted from reference 63 with permission.
The commensal enteric flora can confer adverse and/or beneficial effects on human health. These effects are illustrated on a continuum representing the typical abundance of these species. Adapted from reference 15 with permission from the American Society for Nutritional Sciences.
The commensal enteric flora can confer adverse and/or beneficial effects on human health. These effects are illustrated on a continuum representing the typical abundance of these species. Adapted from reference 15 with permission from the American Society for Nutritional Sciences.