By sampling a year's worth of diapers from fourteen different babies — yes, that was somebody's job — researchers in the labs of Dr. Patrick Brown and Dr. David Relman mapped out histories for each child, telling which bacteria were present, and when, starting from the day they were born.
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The scientists figured out just what bacteria resided in the diapers via a genetic technique called microarray analysis that allowed them to identify more than 2,000 different bacterial species in one single test.
The results: Bacteria that predominated in stool varied widely from baby to baby, and from month to month.
This was unexpected — because although the average person has hundreds, if not thousands, of species of bacteria colonizing his or her digestive system, the same common bacterial families appear over and over in almost all of us and don't really change over the years.
By the end of the babies' first year, however, the profiles did look more and more similar to each other and to what scientists see in adults.
When babies are born, their digestive systems are completely free of bacteria, but within days, a few intrepid species have settled in. These pioneers are followed by waves of new species. The types of bacteria seen early on might thrive in the oxygen-rich environment of the newborn gut, Relman says. But as they consume the oxygen and spread throughout the intestine, they make the area hospitable for the species that eventually take over permanently.
It could be, Relman adds, that many types of these oxygen-loving "starter" bacteria are capable of doing the initial, gut-colonizing job. Geneticist Chana Palmer, a graduate student in Dr. Brown's lab and first author of the paper, says the path is now clear for studies into how factors such as formula-feeding or premature birth might affect microbial patterns. Some very premature babies suffer from gastrointestinal diseases that can be life-threatening, she adds, and it's possible that there could be a microbial component to them.
The study was published this week in the journal Public Library of Science and you can view it for free on the Web or print it out.
— Chelsea Martinez