Escherichia coli is an important component of the normal bacterial community in humans and animals. However, in recent years, the pathogenicity of some virulent strains to the outside of the intestine has been confirmed in clinical medicine. The purpose of this study was to analyze the effect of cyaA gene knockout on the biological characteristics and pathogenicity of extraintestinal pathogenic E. coli. In this study, ExPEC strain (XJ10) was isolated from the lung tissue of sheep with respiratory tract infection, and the mutation strain and complementary strain of cyaA gene were constructed. Real-time PCR analysis showed that expression levels of most genes related to carbon source utilization and adhesion invasion were down-regulated in the cyaA mutant compared to the wild type; Quantification of the number of colonies showed that cyaA mutation results in the number of adhesion and invasive to TC-1 cells colonies decreased compared with wild type; Finally, as the cyaA gene mutated, the value of the LD50 increased as compared to wild type, based on the LD50 calculation. Taken together, mutations in the cyaA gene reduce growth rates, resulting in down-regulation of the transcription levels of genes associated with carbon source utilization and adhesion invasion, and a marked reduction in virulence.
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