Babies born by Caesarean
section may miss out on many of mom’s helpful gut microbes. Instead, these infants’
guts harbor more bacteria that commonly lurk in hospital rooms, scientists
found.
The finding, described September 18 in Nature, adds weight to the idea that C-sections, and the antibiotics that often come with the procedure, may change the type of bacteria that first take up residence in a newborn’s gut. This collection of microbes helps form the microbiome, and details of this early colonization might be important for long-term health, some scientists suspect.
Still, the results shouldn’t
dissuade women from receiving C-sections if needed. “Caesarean sections are a
life-saving and medically necessary intervention,” says Lisa Stinson, a
molecular microbiologist and reproductive biologist of the University of
Western Australia in Perth. But “we need a better understanding of their
long-term effects on infants.”
Microbiome imbalances have
been linked to disorders such as asthma, allergies
and other inflammatory diseases (SN:
2/17/17). But scientists don’t know whether a baby’s nascent microbiome could
ultimately influence these disorders. Nor is it clear whether birth details
change that early microbial colonization.
To get a snapshot of these
early bacterial moments, genomicist Yan Shao of the Wellcome Sanger Institute
in Cambridge, England, and colleagues studied the gut bacteria living in 596
full-term, healthy babies born in U.K. hospitals. In the 314 babies born
vaginally, helpful gut microbes such as Bifidobacterium
and Bacteroides made up 68 percent on
average of the total gut bacteria. These bacteria were scarcer in the guts of
babies born by C-section. Instead, species commonly found in hospital settings,
including potentially harmful Enterococcus and Clostridium, accounted for
an average of 68 percent of the total gut bacteria.
Surprisingly, neither group
of babies had much bacteria from their mothers’ vaginas, an absence that calls
into question the usefulness of delivering vaginal microbes to newborns (SN:
3/30/16). Smearing vaginal fluids onto babies born via C-section has been studied
as a way to restore normal gut microbiota. But the new study “found no evidence
to support controversial ‘vaginal swabbing’ practices,” Shao says.
Along with the birth mode
itself, antibiotics delivered during birth also shape which bacteria set up
shop in an infant’s gut, the study suggests. In many places, mothers who
undergo C-sections receive antibiotics to prevent infections. Along with
removing potential threats, these drugs can kill helpful bacteria. In the
study, babies born vaginally but whose mothers also took antibiotics had fewer
helpful Bacteroides bacteria. That
suggests that some of the bacterial differences are “related
to maternal antibiotic exposure —
not lack of exposure to vaginal bacteria at birth,” Stinson says.
Antibiotics could also affect the microbial mixtures in mothers’
breast milk, Stinson says, which could then influence babies’ gut microbiomes.
In the study, breastfeeding had a small effect on babies’ gut bacteria.
As the babies grew older and
began eating solid food, differences in gut bacteria composition shrank,
researchers found by looking at a smaller set of the babies.
During the study, all of the
babies were healthy. It’s not known whether the bacteria that have the
potential to cause infections in these babies would actually cause trouble
later in life. Even so, starting out life with the wrong repertoire of microbes
likely has consequences, says microbiologist Maria Dominguez-Bello of Rutgers
University in New Brunswick, N.J.