Construction And Biological Characteristic Of FimC Gene Deletion Mutant Of Chicken Escherichia Coli

Chicken colibacillosis is a focal or systemic disease that caused by Escherichia coli. The ecesis of bacteria is mainly through the adherence factor-fimbria. Chicken Escherichia coli mainly have two types of fimbria, typeⅠpili and P pili. It is generally considerd that bacteria settles down on the tracheal epithelium mainly depend on typeⅠpili through the process of pathopoiesis and P fili effect in the further step.Researches indicated that typeⅠpili of human colibacillus is main agent of infecting adhesion. FimC proteinum coding of fimC gene is main subunit of typeⅠpili. It mediates assembly of the typeⅠpili and is indispensable constitution of the assembly process. Mutation of fimC gene can make the fimbria lose the function of synthesis. People have already procured fimC gene that is similar to human colibacillus from chicken Escherichia coli, and the fimC gene from chicken had high homology to that from human. In order to determine further effect of fimC gene of Chicken Escherichia coli O2, fimC deletion mutant was constructed.ΔFimC gene was amplified by PCR and cloned into a suicide vector pCVD442, which containing the pir-dependent R6K replicon and sacB gene. The recombinant plasmid pCVD442::ΔfimC was transformed into a host cell SM10λpir, then conjugated from SM10(pCVD442::ΔfimC) into E.coli O2. Because a homologous recombination would take place betweenΔfimC and fimC which located on the genome, the strain of E.coli O2 fimC deletion mutant was screened out.We study characteristic of the deletion mutant through fimbria expression test, adhesion test and chicken pathogenicity test. The fimbria expression test demonstrated that a great deal of typeⅠpili was produced after the parent strain was cultured at 37℃for 72 h, but little pili of the deletion mutant strain was produced in the same condition. The adhesion test demonstrated that the adherence ability of the mutant strain was apparently subdued, and the adherence ability of the mutant strain is 1/50 of the parent strain. The animal experiment indicated that pathogenicity of the mutant strain was much lighter than that of the parent strain, but still had some virulence. Fatality rate of the parent strain is 6/8, while that of the deletion mutant strain is 2/8.Construction of deletion mutant strain through gene knock-out establishes material foundation to study effect of fimC gene in pathopoiesis mechanism of chicken E.coli and other biological Characteristic functs of fimC gene deletion mutant strain.