O Antigen Identification Of Avian Pathogenic Escherichia Coli And Construction Of Tsh Expression Vector In The South Of Hebei Province

Avian colibacillosis is one of the major bacterial diseases that caused by multipleserotypes of avian pathogenic Escherichia.coli (APEC), including respiratory tractinfection, septicemia, omphalitis, swollen-head syndrome, enteritis, and cellulitis, whichare responsible for significant economic loses in the chicken industry. Avian pathogenicE. coli (APEC) strains belong mainly to serogroups O1, O2, and O78. The pathogenesisand role of virulence factors present in these strains have not yet been fully elucidated,although considerable progress has been made in recent years to establish themechanisms of pathogenicity.The main virulence factors contain Capsularpolysaccharide, lipopolysaccharide complexes, iron uptake system, outer membraneproteins, toxins, outer membrane protein, AGL-3genomic island, invasion IbeA, Pstsystem, colicin etc.Several studies have identified genes encoding virulence factors of APEC．Geneinactivation experiments confirmed a role in the pathogenicity of APEC for type I and Pfimbrial adhesins，for aerobactin iron transport system，and for the temperature-sensitivehemagglutinin Tsh．Expression of adhesins is considered to be anessential virulence traitfor the infectious process of these strains since they are fundamental for the adherenceto the epithelium of birds.The principal adhesins described for APEC strains are type1,P, curli fimbriae and Tsh hemagglutinin.Type1and P fimbriae are encoded by the fimand pap gene clusters, respectively, that are located on the E.coli chromosome, and thepresence of the tsh gene, which mostly located on the Colv plasmid, encoding atemperature-sensitive hemagglutinin in an E.coli strain was first demonstrated byProvence and Curtiss, who suggested that, because of its hemagglutinating capacity, itcould act as an adhesin in the initial stages of colonization of the avian respiratory tract.The in vivo results from infection studies further support the likelihood that Tsh plays arole in colonization in the air sac.All clinical isolates has carried on a series routine tests, including biochemicalidentification、drug sensitive test and serotype identification, the result showed all43stains varying different resistance to10kinds of antibacterial drugs, and resistant strainreached100%.The rate of drug resistance to erythromycin and ampicillin reached100%.Except for amikacin（13%，13/43）, bacterial resistance to drugs were more than 50%, furthermore, strains have high rates of drug resistance to ciprofloxacin、Compound sulfamethoxazole, Carbenicillin, reached90%. The serotype identificationtest showed the main serum type is O2and O78. Besides, taking plasmid DNA ofEscherichia coli as template, designed degenerate primers according to tsh gene fromgenebank, then amplified complete tsh gene by PCR and constructed plasmid vector,ultimately, the vector was introduced into DH5α competent cell and then identificated it.