Newborns may get "good" germs from mom at birth

Newborns may be inoculated with "good" bacteria during birth, and those delivered by Caesarian section may be missing out, researchers reported on Monday.

Their study showed that babies born vaginally were coated in their mother's own benign bacteria, while those delivered surgically had more generic skin bacteria.

This could help explain why C-section babies are more likely to develop dangerous infections such as drug-resistant Staphylococcus aureus, Elizabeth Costello of Stanford University in California and colleagues said.

It could even explain studies suggesting that C-section babies grow up to have higher rates of allergies and asthma, the researchers reported in the Proceedings of the National Academy of Sciences.

"It's just common sense that a baby that is born vaginally is exposed to different bacteria than a baby that is born by Caesarian section. Everyone has a unique set of bacteria," Costello said in a telephone interview.

The amniotic fluid that supports a baby in the womb is usually sterile if the mother is healthy. But in the minutes during and after birth, babies become colonized inside and out with millions of bacteria, viruses and other organisms.

"It is natural and beneficial for us to be colonized by healthy bacteria starting at birth. Most bacteria living in or on us are, if not hurting us, helping us in some ways," Costello added.

For instance, gut bacteria help digest food and protect against disease-causing pathogens.

"In a sense, the skin of newborn infants is like freshly tilled soil that is awaiting seeds for planting -- in this case bacterial communities," said Noah Fierer of the University of Colorado, who worked on the study.

Genetic analysis
The team, led by Maria Dominguez-Bello of the University of Puerto Rico, tested nine women and their 10 newborns at a hospital in Venezuela.

The babies were swabbed within 24 hours of birth and the researchers sequenced the genes of all the bacteria they found.

Babies born vaginally had bacteria identical to their mother's vaginal bacteria on their skin, in their noses and throats and in their fecal matter. But babies born by C-section had bacteria seen more commonly on the skin, and these microbes did not seem to come from the mother.

"We don't know if those skin-like bacteria are coming from the first person to handle the baby -- father or doctor -- or if they were in the air," Costello said.

But what bacteria get on a newborn could have profound health consequences down the road. "There are a lot of studies that correlate delivery mode with health outcomes later in life," Costello added.

Now it will be important to track down which bacteria are protective and to follow newborns into childhood to see if there are health differences that can be linked to their first bacteria, Costello said.

In 2004 researchers in Chicago and Los Angeles found that 64% to 82% of newborns with methicillin resistant Staphylococcus aureus or MRSA infections had been delivered by Caesarian.

The University of Colorado team had previously found that people leave a unique trail of germs on objects that they touch, and that a typical person carries about 150 bacterial species on the hands.