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 <i>Enterococcus faecium</i>, in the development of ASD remains unclear. This study aimed to investigate the impact of <i>E. faecium</i> derived from the feces of autistic children on mice. Thirty male BALB/c mice were divided into three groups: control, <i>E. coli</i>, and <i>E. faecium</i> treatment groups. <i>E. faecium</i> 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 <i>E. faecium</i> 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, <i>E. faecium</i> induced neural damage, heightened inflammation, and compromised blood-brain barrier integrity. <i>Enterococcus faecium</i> 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 <i>E. faecium</i> may contribute to gut-brain axis dysregulation in ASD, although further mechanistic studies are warranted.