Bacteria Exposure During Infancy Could Impact Long-term Health
New research suggests that the very first bacteria infants are exposed to could influence their gut microbiome for many years to come. Since previous studies have linked poor gut health with chronic illness, this knowledge could ultimately help inform measures to reduce the risk of autoimmune-related disorders like allergies and type 1 diabetes.
“It’s very exciting,” says Daniel Sprockett, a Stanford University microbiologist not involved with the study. “These experiments fill an important gap in our understanding about how community assembly happens in the gut and how ecological principles apply to the human gut microbiome.”
This study found that in mice, the timing and order of bacteria exposure impacted how the gut microbiome developed and functioned over time. Jens Walter, a microbial ecologist and senior author on the study, says their findings indicate that the same could be true in humans: being exposed to particular bacteria during birth and shortly thereafter might influence an infant’s gut microbiome for many years, along with its risk for chronic disease. The team from the University of Nebraska-Lincoln published these findings in the September 18 volume of eLife.
“All the research points to there being a window of opportunity early in life where the microbiome is important for immune and metabolic development,” Walter says. “C-section, antibiotic use early in life, and formula feeding are all associated with a higher risk of what I call microbe-associated chronic diseases.”
These efforts draw on knowledge from a seemingly unrelated field: ecology. Ecologists have long known that the order of species arrival in an ecosystem — like a forest or a coral reef — influences the interactions and development of that ecosystem over time.
Walter and his colleagues wanted to learn if this idea applied the gut ecosystem. They began by isolating mice in a carefully controlled, germ-free environment and exposing them to various bacterial strains, varying the order and timing. They found that both factors — timing and order — influenced the eventual makeup of the gut.
Walter and his collaborators’ findings could help explain some of the enormous variability found in the human microbiome. Like a fingerprint, each human microbiome is completely unique — even in identical twins. While some of this variability is related to diet, genetics, and lifestyle, studies indicate that less than 30 percent of the variability observed in the gut microbiome can be explained by these factors.
This new study suggests that differences in timing and order of bacteria exposure in early life could be another piece of the variability puzzle. Fortunately, Walter notes, bacteria exposure is something that humans have at least some control over.
“There is rationale to control this process,” Walter says. “We are clearly interrupting it in this modern world through our extremely hygienic lives. We are not really acquiring a microbiome like animals do or our ancestors would have done for hundreds of millions of years.”
Like Walter, other microbiologists have suggested that by increasing sanitation and reducing early childhood infections, people in Western countries might also be exposed to fewer helpful microbes that bolster the immune system. This theory, called the hygiene hypothesis, is a possible explanation for the increased incidence of autoimmune diseases and allergies in Western countries. By trying to keep out the bad microbes, society may just be shutting out ones the human body needs to develop strong, protective immunity.
“For example, the use of prophylactic antibiotics early in life. There’s a growing recognition that this does not come without cost,” Sprockett says. “It doesn’t mean it’s bad or shouldn’t happen, but just that there are consequences.” Eventually, Sprockett says, new information about the long-term impacts of those decisions “could change the benefit-harm estimation that physicians go through when they’re prescribing those types of antibiotics.”
Sprockett also says that a better understanding of gut microbiome development could influence parental decisions about delivery options during childbirth, infant feeding, and other choices that impact bacteria exposure.
“I’m actually a new father myself,” Sprockett says. “There is quite a wide range of parenting behaviors that may affect [microbial] assembly. I’m very hopeful that behavior modification or therapeutic interventions will eventually be possible.”