The Impact On The Pathogenicity Of Chicken Pathogenic E.coli In The Absense Of QseC Gene

Avian pathogenic Escherichia coli (APEC) is the pathogen of colibacilosis in poultry that bring many types diseases to all the chickens. Colibacillosis is a very common infectious disease in poultry and can produces the significant economic loss over the world.Bacterial resistance has received wide concern due to the public health, especially to APEC. The drug-resistance of APEC has brought great challenge to prevention and treatment of colibacillosis in chicken. Therefore, finding new antibacterial drug targets to cope with the increasingly serious situation is imminent.Drugs targeting bacterial virulence has obvious advantages. The drugs eliminate bacterial virulence without killing bacteria, that can delay and avoid the generation of bacterial drug resistance phenomenon as far as possible. This study investigates the qseC gene’s influence on pathogenicity of APEC, providing new breakthrough for the development of new antibacterial drug targets.To clarify the relationship between the quorum sensing mediated by Qsec in APEC and its pathogenicity. After succefully constructing qseC gene deletion mutant (WTAqseC) of avian pathogenic Escherichia coli in our lab, the qseC gene complementary strain (WT△qseC:pBADqseC) were constructed in this study. PCR, Southern blotting and DNA sequencing demonstrated it was successfully constructed.In vitro assays (growth curve, in vitro competition assays, guinea pig erythrocytes adhesion assay and quantitative PCR analysis, etc.) and in vivo assays (LD50 determination, the amount of bacteria in the infected tissues, in vivo competition experiments, the survival rate of infected mice, etc.) were both used to evaluate the influence of qseC gene deletion on the pathogenicity of chicken Escherichia coli.In vitro assays showed that the growth rate of WT△qseC is reduced compared with that of the wild-type strain, while the growth rate of WT△qseC:pBADqseC significantly increased. In vitro competition parameter of wild-type strain and WT△qseC in the competition assay is 0.67, while that of the wild-type strain and WT△qseC:pBADqseC is 1.14. compared with the wild-type strain, hemagglutination titer of WT△qseC decreased 50%, the type Ⅰ pili associated genes downregulated; while that of WT △ qseC:pBADqseC restored to the level of wild-type strain, and expression level of some type Ⅰ pili related genes in WT△qseC:pBADqseC rise.In vivo assays showed that the LD50 of WT△qseC decreased by about 2.14 times compared with that of the wild-type strains, while that of the WT△qseC:pBADqseC recovered to the level of the wild type strain; the bacterial counts of WT△qseC in spleen, liver, lung tissue of the infected mice were lower than those of wild-type strains, while the bacterial counts of WT△qseC:pBADqseC significantly improved compared with those of WT△qseC, and restored to the levels of the wild-type strain. The survival ability of WT△qseC in the organs of mice reduced compared with that of wild-type strain, while the level of WT△qseC:pBADqseC then recovered or exceed that of the wild type strain. The survival rate of WT△qseC in the infected mice improved compared with that of the wild type strain, while that of WT△qseC:pBADqseC decreased, and returned to the level of the wild strain.In conclusion, these data in vitro and in vivo suggested that qseC gene deletion significantly reduced the growth rate, the growth capacity, adhesion ability to the red blood cell of the guinea pigs, and in vivo pathogenicity of chicken pathogenic Escherichia coli. The study also provides new ideas for discovery and development of new antibacterial drug targets based on quorum sensing signal molecule inhibitors.