Babies' First Bacteria Depend on Birthing Method

A new study indicates different delivery methods of newborn babies has a big effect on the types of microbial communities they harbor as they emerge into the world, findings with potential implications for the heath of infants as they grow and develop.

The study, led by the University of Puerto Rico and involving the University of Colorado at Boulder and two Venezuelan institutes, showed that babies delivered vaginally had bacterial communities resembling their mother's vaginal bacteria, while Caesarian section newborns had common skin bacterial communities. Researchers believe many of the different microbial communities residing on humans -- each of which is personally unique -- may help protect individuals from various diseases.

The new findings establish an important baseline for tracking the succession of bacterial communities on babies and their associated effects on human health, said co-lead study author Maria Dominguez-Bello of the University of Puerto Rico.

The new study appears in the June 21 issue of the Proceedings of the National Academy of Sciences. Former CU-Boulder researcher Elizabeth Costello, now at Stanford University, was co-lead author on the study. Co-authors included CU-Boulder Assistant Professor Noah Fierer, CU-Boulder Assistant Professor Rob Knight, Monica Contreras of the Venezuelan Institute for Scientific Research and Magda Magris of the Amazonic Center for Research and Control of Tropical Diseases in Venezuela.

Dominguez-Bello said the bacterial communities of C-section babies were dominated by species from the Staphylococcus genus, most of which are harmless but a few of which can cause severe infections. "These differences we are seeing in this study might be related with increased health risks in C-section babies, although more research is needed," she said.

Previous studies indicate babies born via C-section can be more susceptible to certain pathogens, allergies and asthma than newborns born vaginally. The PNAS study results may help explain the higher incidence of Methicillin-resistant Staphylococcus aureus, or MRSA, in C-section babies, a hard-to-treat bacterial infection that has been increasing in hospitals and clinics in recent years, according to the researchers.

In a 2004 study undertaken in Chicago and Los Angeles County hospitals, between 64 percent and 82 percent of reported cases of MRSA skin infections in newborns occurred in C-section infants. While the World Health Organization has recommended the percentage of births via C-section not exceed 15 percent in any country because of potential medical complications, the rate is much higher in a number of countries, including China at nearly 50 percent and the United States at about 30 percent.

Human microbial communities play an important role in digestion and immune health and are believed to collectively endow us with the essential traits we rely on for such functions, according to the research team. One possibility is that the direct transmission of a mother's vaginal bacteria onto newborns may act as a defense against diseases by limiting the colonization of more harmful pathogens, they said.

In a related 2009 study led by Knight, researchers developed the first atlas of microbial diversity across the human body in adults, charting wide variations in microbe populations from the forehead and feet to noses and navels of individuals -- differences that were not yet apparent in the PNAS newborn study. One goal of the human bacterial studies is to find out what is normal for healthy people, which should provide a baseline for studies looking at human disease states, said Knight.

"The prospects of learning how differences in individual human microbial communities can be used as a diagnostic tool in biomedicine is frankly quite exciting," said Knight of CU-Boulder's chemistry and biochemistry department. "With these new data on babies, we now have a second point in time for comparison."

"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 Fierer of CU-Boulder's ecology and evolutionary biology department. "The microbial communities that cluster on newborns essentially act as their first inoculation."