Rotavirus is a contagious enteric pathogen and the leading cause of diarrhoea in infants and children. After ingestion, rotavirus infects the intestinal epithelium, which is colonized by diverse members of the gut microbiota. Shi et al. report that gut segmented filamentous bacteria (SFB) prevent and cure rotavirus infection in immunodeficient mice. The authors unintentionally developed a mouse breeding colony that was highly resistant to rotavirus infection and hypothesized that the gut microbiota conferred resistance. Accordingly, resistance was transferred by co-housing and faecal microbiota transplantation. The authors used filtration, heating, antibiotics and limiting dilution to identify SFB as the protective component of the microbiota. Protection was independent of previously observed rotavirus-restricting immunological factors. Instead, SFB caused changes in host gene expression and enhanced gut epithelial turnover, and SFB-containing faeces reduced rotavirus infectivity in vitro, suggesting that SFB could be used to combat rotavirus infections.