The NMGCF-19 strain is an E.coli strain isolated and identified in our laboratory from lambs manifesting severe diarrhea and meningitis.Previous analysis of the genome sequence of NMGCF-19 strain showed that the outer membrane protein A(ompA)gene was a potential viru-lent gene.In order to determine whether the ompA gene is associated with the pathogenicity of NMGCF-19 strain and the underlying mechanism,the NMGCF-19 strain with ompA knockout(NMGCF-19△ompA)was generated in this study using CRISPR/Cas9 technology and used to de-termine the role of ompA gene in mediating the encephalitis by NMGCF-19 infection and the un-derlying mechanism using the mouse model system.The results showed that the neuronal cell nec-rosis in the hippocampus in mice infected by NMGCF-19△ompA was significantly reduced and was not focal compared with that of mice infected with the wild-type NMGCF-19 strain.The number of bacteria in brain of mice infected by NMGCF-19 △ompA was significantly reduced in comparison to that of mice infected by NMGCF-19.Simultaneously,the mRNA and protein expression levels of the tight junction proteins ZO-1 and Occludin were both increased in mice infected by NMGCF-19 △ompA strain compared with the mice infected by NMGCF-19 strain.These results suggest that the ompA gene is a virulent gene and plays an important role in the invasion of the blood-brain barrier by NMGCF-19 strain in mice.