| The mammal endogenous intestinal microbiota plays a fundamentally important role in health and disease, yet this ecosystem remains incompletely characterized and its diversity poorly defined. Critical functions of the microbiota include protection against epithelial cell injury, regulation of host fat storage, stimulation of intestinal angiogenesis and competition against pathogen colonization. Establishment of intestinal colonization is the first step in the pathogenesis of many gastrointestinal pathogens. The pathogen must be able to establish itself in the face of competition from the complex microbial community that is already in place. It is not known if the introduction of a pathogen causes detectable changes in the overall ecologic structure of the intestinal microbial community.Because of the insensitivity of cultivation, investigators have begun to explore this ecosystem using molecular fingerprinting methods. Denaturing gradient gel electrophoresis (DGGE) targeting 16S rRNA-encoding genes was developed as rapid methodologies with high throughput that are more suitable for analysis of complex microbial communities. Although phylogenetic identification of specific members of a community is difficult, DGGE can rapidly provide information regarding the richness and evenness of a complex community.In this study, we used 16S rDNA-based DGGE analysis to monitor the community structure of the microbiota of the murine cecum during the establishment of colonization by the fungal pathogen Candida albicans. Female SPF BALB/c mice are treated for 5 days with ceftriaxone in the drinking water, followed by a single oral gavage of C. albicans SC5314. This results in alterations of intestinal bacterial populations and increased yeast C. albicans numbers in the intestinal microbiota for at least 7 days. The analysis of DGGEcombined with universal (V3 and V6~V8) 16S rDNA primers indicated that colonization of the murine cecum by C. albicans SC5314 was associated with a decrease in the overall diversity of the bacterial community, in large part due to changes in richness resulting from the inhibition of recolonization of the predominant sub-populations. The genera or group-specific (targeting the genera Bifidobacterium, Enterococcus and the Lactobacillus group, which also comprises the genera Leuconostoc, Pediococcus and Weisella) 16S rDNA primers were used to characterize the detailed variations of subpopulations of intestinal microbiota. After colonization of the murine cecum by C. albicans SC5314, DGGE profiles clearly indicated that, compared with only antibiotic-treaed mice and control mice, the Enterococcus population was significantly decreased (P<0.05);compared with only antibiotic-treaed mice, Lactobacillus group showed no significantly variation (P>0.05) and Bifidobacterium populations were completely inhibited.In conclusion, we used 16S rDNA-based DGGE analysis to provide the first detailed examination of the microbial ecology of the murine intestinal tract during invasion by a C. albicans. The results demonstrate that invasion of the complex gastrointestinal microbial community by a fungal pathogen Candida albicans causes reproducible and significant disturbances in the community structure. The use of non-culture-based methods to monitor these changes should lead to a greater understanding of the ecological principles that govern pathogen invasion and may lead to novel methods for the prevention and control of gastrointestinal pathogens.
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