Autistic People Have Higher Levels of Specific Gut Bacteria

Researchers found that autistic people have a higher abundance of gut bacteria associated with symptoms of ASD, including social behavior dysfunction and repetitive behaviors.

Over the past two decades, scientists have discovered significant links between bacterial and fungal diversity in the digestive tract and several health conditions.

For instance, reports suggest that the gut microbiome may play a role in the development of certain cancers and GI issues like irritable bowel syndrome (IBS).

What's more, imbalances of fungi in the gut biome have been linked to attention deficit hyperactivity disorder (ADHD).

Autism spectrum disorder (ASD) may also have ties to the gut microbiome. For example, a 2023 study found a microbial signature in the GI tracts of autistic people that differs from non-autistic individuals.

Now, scientists from the Azrieli Faculty of Medicine of Bar-Ilan University have found that autistic individuals have a higher abundance of a specific bacteria in their gut microbiomes. When the researchers treated newborn mice with this bacterium, they began to display symptoms of ASD.

The study, recently published in npj Biofilms and Microbiomes, examined the gut microbiome diversity in 96 participants with ASD and 42 non-autistic people. They found a significant increase in alpha diversity and a higher abundance of phylum Bacteroidetes and genus Bacteroides in individuals with ASD.

To understand more about the impacts of an overabundance of Bacteroides, the research team gave newborn mice Bacteroides fragilis and allowed it to colonize in the gut.

They found that male mice treated with B. fragilis showed social behavior dysfunction, an increase in repetitive behaviors, and gene expression dysregulation associated with autism in the prefrontal cortex of the brain.

However, female mice did not display behavioral deficits, which suggests that males may be more vulnerable to environmental factors that contribute to ASD.

While B. fragilis colonized in the mice for up to two weeks after treatment, it was no longer present in the rodents' microbiomes at eight weeks. Still, the behavioral and molecular changes remained, which the researchers suggest may indicate that B. fragilis can affect brain development.

Overall, the research team says these findings suggest that overabundance of Bacteroides early in life may have functional consequences for autistic individuals.

Is gut microbiome imbalance a driver for autism?

A 2023 analysis of published data on the links between autism and the gut microbiome concluded that this area of research "has enormous potential and merits intensified focus and investigation."

This latest study adds more evidence that the bacterial composition in the gut appears to play some role in ASD.

According to the study's authors, the genus Bacteroides, including B. fragilis, are essential for human health. However, an overabundance of this species can cause issues.

For example, some strains of B. fragilis emit a toxin that may increase gut permeability and may lead to a condition known as leaky gut. When this condition occurs, it can negatively impact brain function.

Moreover, when the scientists examined gene expression in the prefrontal cortex of the adult male mice, they found a downregulation of genes that previous research suggests may be a biological driver of autism.

Although more research is needed, these findings open the door to future studies looking into whether gut microbiome-based treatments during early childhood could potentially prevent brain changes associated with autism.