Early-life gut bacteria help shape a baby’s immune system and protect against diseases such as inflammatory bowel disease and asthma later in life. Now, a study in mice revealed that a mother’s oral microbiota may increase the risk of such conditions in the offspring.

The findings, published in Cell Reports, suggest that the maternal oral microbiota plays a key role in influencing infant gut health and disease risk.

Babies get much of their first gut bacteria from their mothers—through birth, breastfeeding, and close contact. These microbes come from various parts of the mother’s body, and if harmful bacteria are passed to the baby, they may raise the risk of gut inflammation and disease. However, how exactly these bacteria persist in the infant gut, and how they contribute to disease, is still unclear.

Researchers led by Masafumi Haraguchi at University of Michigan in Ann Arbor set out to investigate how mothers with an imbalanced mouth microbiota influence the community of gut microbes in their offspring.

Immune imprinting

The researchers caused gum disease in mother mice, which led to the growth of a harmful oral bacterium called Klebsiella aerogenes. This bacterium was passed to the mice’s pups and colonized their guts during the first weeks of life. However, the microbe disappeared as the pups’ guts became more diverse with age. 

Klebsiella aerogenes changed the pups’ immune environment in the gut, increasing certain immune cells that can cause inflammation. The early exposure to the bacterium also affected how genes related to inflammation and metabolism work in the gut, the researchers found.

Compared to pups born to healthy mothers, those born to mothers with oral infections showed worse symptoms and inflammation when their guts were challenged. This increased risk appears to come from the early “immune imprinting” caused by exposure to the mother’s oral bacteria. 

Mouth health

Even after the harmful bacteria disappeared as the pups grew, some immune imbalances persisted into adulthood, making the animals susceptible to gut inflammation. 

“Our results provide compelling evidence that maternal oral health, particularly the presence of oral dysbiosis, significantly influences the development of gut microbiota and the immune system in offspring, ultimately impacting health outcomes from infancy through adulthood,” the researchers say.

Although it’s unclear whether the effects observed in mice translate to humans, the authors add, the findings highlight the importance of good oral health in mothers during pregnancy and early childcare to support healthy gut development and prevent immune-related gut problems.