Question

. Why was Escherichia coli thought to be a dominant member of the human gut microbial community in the past? What populations ARE important in the human gut and what evidence do we have that the specific bacteria present are important for human health?

Answer 1

Escherichia coli or E. coli is a rod like bacteria that generally found in the lower intestine of the warm blood animals. It was categorized in the gram negative bacteria and survives in facultative anaerobic condition. In lower intestine it find most suitable environment to survive and due producing vitamin K2 in gut it live symbiotically. Some strains of E. coli are pathogenic and they cause the diarrhea and urinary tract infections that sometimes lead to the death. It having generation time approximately 19 minutes under the optimal condition and rapidly divide. Earlier, due to lack of sophisticated techniques, it was thought that it is major human gut bacteria and generally fecal contamination in potable water is checked by the presence of E. coli base biochemical assays and food contamination also monitored through this. Even nowadays it is also considered best source to detect the fecal /sewage contamination in potable water.

Later on several microorganisms studied that present in the gut microflora and later on scientist decide that E. coli constitute only 0.9 % microbial population of gut. Apart from E. coli several other microorganisms survive in gut micro-flora but isolation technique has limitation that only 10-25 % organism of gut has been identified. Initially it was thought that gut contains 500-1000 microbial species but now it realizes that it having ~35000 species.   Some common species that have identified recent metagenomic approach is, Butyrivibrio crossotus, Bacteroides , navus, Akkermansia (Verrucomicrobia): Ruminococcus Akkermansia sp., Anaerotruncus colihominis, Ruminococcus and Fecalibacterium sp. Etc

Some bacteria such as Bacteroides, Fecalibacterium, Bifidobacterium, Roseburia, and Enterobacteria helps in the short chain fatty acid synthesis such as butyrate, acetate, propionate and these are the rich source of the energy.

Butyrate produced by the bacteria prevent the desposition of D-lactate in gut. Different members of Bacteroides genus synthesize several glycolytic enzymes that help in the degradation of several complex carbohydrate in food.

Several members participate in vitamin K and vitamin B synthesis.

Some bacteria of gut sucha as Eggerthella lenta are capable to metabolize the xenobiotic compounds. Apart from this Lactobacillus innocua, Bacteroides thetaiotaomicron, lactobacillus sp. Bacteroides thetaiotaomicron etc produce various acids, unfavorable conditions and initiate the immune system so it protect from the other pathogenic microorganisms.

That's why these gut microflora is important for the good human health