Neurodevelopmental disorders, including autism spectrum disorder (ASD), are 
defined by core behavioral impairments; however, subsets of individuals display 
a spectrum of gastrointestinal (GI) abnormalities. We demonstrate GI barrier 
defects and microbiota alterations in the maternal immune activation (MIA) mouse 
model that is known to display features of ASD. Oral treatment of MIA offspring 
with the human commensal Bacteroides fragilis corrects gut permeability, alters 
microbial composition, and ameliorates defects in communicative, stereotypic, 
anxiety-like and sensorimotor behaviors. MIA offspring display an altered serum 
metabolomic profile, and B. fragilis modulates levels of several metabolites. 
Treating naive mice with a metabolite that is increased by MIA and restored by 
B. fragilis causes certain behavioral abnormalities, suggesting that gut 
bacterial effects on the host metabolome impact behavior. Taken together, these 
findings support a gut-microbiome-brain connection in a mouse model of ASD and 
identify a potential probiotic therapy for GI and particular behavioral symptoms 
in human neurodevelopmental disorders.