LONDON (Xinhua) -- Researchers have found evidence that baby mice squeezing through the birth canal swallow bacterial molecules that help their gut grow healthily, according to the latest issue of the Nature.

The finding suggests that kids born by caesarean might miss out, the science magazine said.

Swarms of friendly bacteria normally live in our guts, and cells lining the intestinal tubes do not attack them, researchers in Germany were quoted in saying.

The researchers have found that, in mice at least, these intestinal cells 'learn' not to harm the bugs sometime around birth.

The researchers extracted intestinal cells from mice embryos before birth and exposed them to a component of bacteria, and the embryonic cells reacted and produced inflammatory molecules, they said, adding but the same gut cells from one-day-old newborn mice or adult mice did not.

The researchers think that bacterial scraps naturally slopping around in the birth canal and mother's feces are swallowed by the baby mice as they make their entry into the world. These molecules pass down into the gut, where they stimulate the gut cells; a single exposure is enough to teach the cells to tolerate friendly bugs in the future.

To show this, the researchers looked at the responses of gut cells of baby mice born both naturally and by caesarean. Those born through the vagina fired up an inflammatory response in the two hours after birth, a sign that their cells had been stimulated by bacterial molecules. In contrast, babies born by caesarean did not show signs of such activation.

But feeding these babies fragments of bacteria after their birth did fire up this response, the researchers said.

This first exposure could teach a newborn infant's gut cells to ignore the harmless bacteria that begin to colonize the intestine in the days and weeks after birth.

In theory, this could mean that the intestines of babies born by caesarean are less welcoming to gut bacteria - perhaps with long-lasting effects for the babies' health, the researchers said.