Autism-Associated Gut Microbiota–Derived Enterococcus facium Modulates Gut–Brain Axis Function and Behavior in Mice

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by social communication deficits, repetitive behaviors, and restricted interests. Although its pathogenesis is not fully understood, emerging evidence suggests a connection between gut microbiota alterations and ASD. The role of specific bacterial species, particularly Enterococcus faecium, in the development of ASD remains unclear. This study aimed to investigate the impact of E. faecium derived from the feces of autistic children on mice. Thirty male BALB/c mice were divided into three groups: control, E. coli, and E. faecium treatment groups. E. faecium was administered orally for 30 days. Behavioral assessments, including open field tests, sucrose preference, Y-maze, and social interaction tests, were performed to evaluate anxiety, depression, memory, and social behavior. Additionally, serum 5-HT levels were measured, and colon and brain tissues were analyzed for inflammation, blood–brain barrier (BBB) integrity, and histological changes. Stool DNA sequencing was used to assess microbiota diversity and composition. Treatment with E. faecium significantly altered behavior in mice, including increased anxiety, depression, impaired memory, and social dysfunction. Colon histology revealed severe damage, including increased inflammation, reduced tight junction protein expression, and decreased mucin-2 levels. Elevated serum lipopolysaccharide (LPS) levels indicated systemic inflammation, and gut microbiota analysis showed significant dysbiosis. In the brain, particularly within the hippocampus and cortical regions, E. faecium induced neural damage, heightened inflammation, and compromised blood–brain barrier integrity. Enterococcus faecium from autistic patients can induce significant behavioral changes in mice, potentially via gut microbiota dysbiosis, intestinal barrier disruption, and brain inflammation. These findings suggest that E. faecium may contribute to gut–brain axis dysregulation in ASD, although further mechanistic studies are warranted.