More on human guts

Yet another interesting open access gut microbe paper in PLoS Biology came out in June. This one describes patterns in the colonization of the intenstines of human infants. As mentioned in a previous post, we are born with a sterile intestinal tract and depend upon the ingestion of compatible microbes for the establishment of our gut community. This study used 16S rhibosomal DNA sequences to document changes in the structure and diversity of infant guts over the first year of life. As with the previous paper, Liza Gross wrote a nice summary article.

Some key points:

• 14 babies were followed (including one set of twins) for one year. Early the communities were quite different but by the end of the first year they had acquired a composition similar to that of the adult human.
• At one week of age, two babies delivered by cesarian had fewer total gut bacteria indicating that during natural child birth, the colonization begins during the birthing process.
• While broadly similar to each other and to the adult community, each infant had a distinct profile that persisted over time.
  

This paragraph from the end of the Gross summary provides a good overview of the most interesting findings:

The idiosyncratic nature of the early stages of colonization suggests that a baby’s initial bacterial profile largely results from incidental microbial encounters. The fact that some of the early stool samples matched their mother’s breast milk or vaginal sample supports this interpretation. Shared environment may also explain the coincidental appearance of microbes in the twins. The researchers explain the tendency of these communities to eventually converge by hypothesizing that the human–microbe symbiosis has likely evolved under strong selection and that certain well-adapted microbes repeatedly “win” the battle over the opportunistic early colonizers.

Selections from the final paragraph describes some of the future directions the work will take:

By comparing the surprising range of microbial profiles found in these healthy babies to the microbiota of infants born prematurely or with health problems, future studies can explore how diet, delivery method, or other factors might spell the difference between health and disease.

and that the approach used in the study will allow us to explore questions about

the environmental and genetic factors that shape and personalize the amazing “alien” ecosystem that lives within us.