Dogs Provide Surprising Benefit to Infants' Gut Bacteria
For many of us, pets are important family members. They give us loyalty, companionship, and comfort. Now, researchers have given us another reason to welcome them into the family: Babies from families with furry pets — the majority of which were dogs — had higher levels of two types of beneficial gut bacteria.
The scientists, led by pediatric epidemiologist Anita Kozyrskyj from the University of Alberta, surveyed mothers about pet ownership in a questionnaire during their second or third trimester of pregnancy and three months postpartum. Then they collected fecal samples from the mothers' 746 infants and analyzed the types of bacteria found within.
Slightly less than half the households owned a pet: 44–48% owned a dog during late pregnancy, or during first three months of baby's life; 34–36% owned a cat; and 7–8% owned some other furry pet.
Exposure to pets in the womb or up to three months after birth increased the abundance of two bacteria, Ruminococcus and Oscillospira. Studies have linked Ruminococcus to reduced occurrence of childhood food allergies, and others have associated Oscillospira in the gut with a a decreased risk of obesity in toddlers and adults.
The researchers found the effect on gut bacteria both when the mother delivered the baby by C-section or vaginally, was bottle-fed or breastfed, and whether the mother had allergies or was given antibiotics during delivery or did not receive them — significant since all of these could have an impact on gut bacteria, as well.
The study team compared gut bacteria in infants from homes with carpets versus no carpets and siblings versus no siblings to rule out other sources of the bacteria. They found no differences in those two data sets.
The effect of pets on infants' gut microbiome occurred indirectly, Kozyrskyj said in a press release — the bacteria aren't put there by the dog. She suspects the bacteria move from dog to mother to unborn baby, during pregnancy as well as during the first three months of the baby's life.
The new study also found that the transmission of group B Streptococcus from mother to baby during a vaginal birth was significantly decreased in newborns with pets in the household. The child can pick up this bacteria through swallowing and aspiration during the birth process. If aspirated, it can cause serious pneumonia.
The study indicates that having a pet in the household before the baby was born — even one who may not be there after — can still affect the baby's gut bacteria.
And the more we learn about gut bacteria, the more we understand how far-reaching its importance is.
The gut bacterial community — the microbiome — of newborns doesn't have many different types of bacteria. Proteobacteria are the most common bacteria in infants guts, but the mode of delivery contributes to their microbiome, as well. Lactobacillus and Prevotella are found more in the guts of vaginally delivered babies, and maternal skin bacteria — Streptococcus, Corynebacterium, and Propionibacterium — are found more in those born by cesarean delivery.
Between age one and three, a child's gut bacteria becomes colonized with types of bacteria that persist through adulthood, particularly those of the Firmicutes and Bacteroides families.
The adult gut has over 400 species of bacteria. There's a delicate balance between types and amount of bacteria in a healthy person, and several things can upset that balance, such as illness and antibiotics.
Studies have associated certain species of bacteria with conditions in children, like obesity and autism, but the cause of this association — why the gut microbiome shifted in composition and if that is a cause or effect of the condition — hasn't been sorted out yet.
Previous studies have found that increased amounts of streptococci present in infants' guts is associated with increased body fat of children at age five to six. Researchers have found the reverse for Bifidobacteria — increasing amounts of this bacteria in infants' guts corresponded to lower body fat in children.
Kids with autism spectrum disorders have higher rates of diarrhea, constipation, and abdominal pain. The presence of autistic symptoms has been associated with lower amounts of the bacteria Prevotella, Coprococcus, and Veillonellaceae in the gut, but the relationship between that finding, gastrointestinal symptoms, and autism isn't clear.
Diet is the most important determinant in shaping the composition and diversity of the gut microbiome throughout adulthood, but antibiotic use — and many other conditions — also alter gut bacteria.
For example, a study of 39 children, about half of whom received multiple courses of antibiotics during the first three years of life, found a lack of Bacterioides in their guts. Early treatment with antibiotics had caused a long-lasting disruption of the normal gut microbiome that can have health effects.
From weight to antibiotics — and now to pets — a continual barrage of influences shapes our gut microbiome. We are just starting to make associations between gut bacteria and disease, and other health conditions, both healthy and unhealthy. Hopefully, scientists will be able to bring meaning to these connections and help us know how to influence our gut microbiome in a positive way.
Because of the work by Anita Kozyrskyj and her colleagues, we now know that our gut bacteria may be affected even before we are born.