Role Of The Gut Microbiota During Enterohemorrhagic Escherichia Coli Infection

The mammalian intestine is colonized by millions of microorganisms,most of which are bacteria that have co-evolved with the host in a symbiotic relationship.The collection of microbial populations that reside on and in the host is commonly referred to as the microbiota.A primary function of the gut microbiota is to protect the intestine against colonization by exogenous pathogens and potentially harmful indigenous microorganisms via several mechanisms,which include direct competition for limited nutrients and the modulation of host immune responses.Breakdown of the normal microbial community increases the risk of pathogen infection,the overgrowth of harmful pathobionts and inflammatory disease.Exploring the interaction of the microbiota with pathogens and the host might provide new insights into the pathogenesis of disease,as well as novel avenues for preventing and treating intestinal infectious diseases.Given this,more and more researchers target the gut microbiota,hunting for new therapies to treat intestines diseases.Now,although fecal microbiota transplantation(FMT)is capable of curing enterohemorrhagic Escherichia coli(EHEC)infection,the method has many disadvantages;thus,to explore more safe and effective ways for the disease,we attempt to excavate small moleculars derived from the gut microbiota and the host as a substitution to treat disease resulted from the pathogen infection.The study carride out in two stratifications: firstly,gut commensals relevant to EHEC infection were preliminarily screened;secondly,the enteric metabolites relevant to EHEC infection were preliminarily screened.Part 1.Screening of gut bacteria relevant to EHEC infectionIn the trial,we pretreated the mice with vancomycin and streptomycin to detect the role of different components in defesing EHEC infection.The results displayed that the mortality ?weight change ?feces EHEC burden ?Shiga toxin level of mice treated with vancomycin were similar to that of mice without antibiotic treatment(P > 0.05);however,these indicators(except for weight change)of mice treated with streptomycin were significantly higher than that of mice in control group(P < 0.05),suggesting the deletion of bacteria sensitive to vancomycin does not increase the susceptivity to EHEC,but the loss of bacteria sensitive to streptomycin does.To get more detailed results,the microbe genome in mice feces was extracted,then 16 S r DNA sequencing was undertook and taxonomy of the bacteria contained in each sample was annotated.Analysis of the microbe diversity indicated that species variety of mice pretreated with vancomycin ?streptomycin notably decresed coparing to control;in the taxonomy of phylum,there were three phyla,including Deferribacteres?Proteobacteria?Tenericutes,overlapped in control and group of vancomycin,but there were none phyla overlapped in control and group of streptomycin as well as in group of vancomycin and group of streptomycin;in the taxonomy of genus,comparing to control,the relative abundances of three genera(uncultured bacteria of vadin BB60 family?Alloprevotella? Parasutterella)raised and two genera(uncultured bacteria of S24-7 family?Bacteroides)descented in mice pretreated with vancomycin;while in the group of streptomycin,the relative abundances of above-mentioned five genera changed conversely,hinting that upregulation of vadin BB60 family ? Alloprevotella ? Parasutterella meanwhile downregulation of S24-7 family?Bacteroides have a potential role of protecting the host from infenction by EHEC;Otherwise,infection by EHEC may be promoted.Part 2.Screening of enteric metabolites relevant to EHEC infectionWe attemptted to hunt for some clues from metabolism following the target genera being found: colonic content of mice in the three group(control,vancomycin,streptomycin)was extracted followed by qualitation and quantitation of hydrosoluble small moleculars.The analysis manifested that a host of compunds contained in the two experimental groups,in which mice were pretreated with 50?g/m L vancomycin and 5mg/m L streptomycin respectively,fairly differed from that in the control group.Compared to the control group,concentrations of Galactonate?Urea?Choline?Sucrose in streptomycin group notably increased while not significantly changed in vancomycin group;Contents of Ethanol in streptomycin group as well as vancomycin group both rised in comparison with the control group,but the amplification of the former(S/N = 4.12,P = 0.009)is super than that of the latter(V/N = 2.32,P = 0.012);Although the quantities of Acetate?Butyrate?Alanine?Propionate in both of the two experimental groups were all more than that of the control group,dampings of these compounds in streptomycin group were larger than that in vancomycin group.Other reseachers' achievement[40-50] signs that Fucose?Acetate?Butyrate play a protective role in resistance to EHEC infection and Propionate has no important effect on the infection by EHEC.On the basis of these proofs,we primarily deem that increases of Ethanol?Galactonate?Choline?Urea?Sucrose accompany with decreases of Acetate?Butyrate?Propionate?Alanine?Glycine?Fucose?Uracil?Hypoxanthine leads to increased susceptivity to infection by EHEC.In summary,we rudimentarily defined five bacteria genera or family(Alloprevotella?Parasutterella?vadin BB60?S24-7?Bacteroides)and some crucial small molecules(Ethanol?Galactonate?Choline?Urea?Sucrose?Acetate?Butyrate?Propionate?Alanine?Glycine?Fucose?Uracil?Hypoxanthine)via utilizing the murine model infected by EHEC and analyzing fecal microorganism diversity and colonic content metabolites.These results suggest new possibilities for futher research of mechanism adoptted by gut microbiota in resisting against EHEC infection.