Abstract: This study aimed to construct rant gene-deleted mutant and complemented strain to study the effect of MFS efflux pump Rant on the resistance of R. anatipestifer. R. anatipestifer RA-LZ01 strain was used as the parental strain. The deletion mutant Δrant was obtained by the suicide plasmid pRE112-mediated homologous recombination, and rant gene was replaced with erythromycin resistance cassette. The E. coli-R. anatipestifer shuttle plasmid pCPRA was used as the vector to construct the complemented strain cΔrant. The minimal inhibitory concentrations (MICs) of 11 classes of clinically common antibiotics against wild strain, deletion mutant and complemented strain were determined with micro broth dilution assay. The growth ability and virulence of the above 3 strains were also determined. The results showed that compared with the wild strain, the MIC value of tetracycline antibiotics to the deletion mutant was significantly reduced, and the MIC values of other antibiotics did not change. The growth rate of the deletion mutant was significantly reduced by comparison with that of the parental strain. Furthermore, the deletion of the rant gene significantly reduced the virulence of R. anatipestifer. These results indicate that rant gene of R. anatipestifer mediates the efflux of tetracycline antibiotics and can significantly affect the growth and virulence of R. anatipestifer.

Key words: Riemerella anatipestifer, rant gene, resistance, growth, virulence