| Avian pathogenic E. coli (APEC) can lead extraintestinal diseases to chickens, turkeys and a variety of other poultry, such as pericarditis, perihepatitis, meningitis and so on, even can cause sepsis to death. Birds up to 7-30 days of age are the most susceptible, adult poultry can’t exempt. It usually leads high diseases (3.8%-42.6%) and high mortality (5%～75%); even very few farms with poor environment can lead to serious mortality (90.3%), our poultry industry has suffering from the threat of the disease. Recently, some reports show that APEC also can cause disease to humans and mammals, even death. Currently, most farms mainly by adding large doses of antibiotics to prevent and control of this colibacillosis, but with the widespread use of antibiotics in the past half a century, APEC has evolved various serotypes of resistant strains, this makes us suffering tremendous pressure.According to the sequences published from NCBI, we designed 18 and 14 pair primers to detect the distribution of virulence genes and resistance genes; we also detected the drug sensitivity, biofilm-forming ability, pathogenicity and serotype distribution of the strains. The virulence genes detection rate of fimC, mat, ibeB, yijp and ompA were 98%,96%,96%,90% and 90%, but detection rate of vat and papC were only 32% and 10%. Resistance genes test results directly show that the resistance gene strA, strB, dhps, sul II, parC wich belong aminoglycosides, sulfonamides, quinolones, tetracyclines were 98%,98%,100%,98% and 100%,respectively.β-lactams’ gene oxal, oxa5 and oxa31were 0%,0% and 4%. Susceptibility test results show that all of the isolates were resistant to antibiotics of tetracycline, clindamycin and rifampicin. Cephalosporin ceftriaxone resistance rate were 16% followed by lactam chloramphenicol resistance rate of 34%. Erythromycin, azithromycin, norfloxacin, cephalothin resistance rates were 90%,82%,82% and 84%. More than half of the strains (66%) tolerate 10 kinds of antibiotics and only a few strains (4%) fully withstand all of antibiotics this test. Biofilm-forming ability test results showed that all of the strains were weak to forming biofilm. According to the slide agglutination results we concluded that 078 serotype was the main serotypes, and it has so difference pathogenicity to 10-day-old Cherry Valley.First of all, APEC mainly through adhesion molecules to combine the specific receptors of certain cell to colonize. Then the relevant invasion factors can help APEC invade into the host cells. And then APEC enter into the blood circulation system to various organs. Finally, with the help of different virulence factors, APEC successful lead disease. Vacuolar transporter toxin (Vat) is one of the major virulence factors of APEC, The protein directly pose the Bacteria’s V secretion system (T5SS), T5SS can transport some secreted proteins related throw its own specific structure into the outer membrane and the whole process does not consume energy. We constructed the vat mutant of APECO1 by the Red recombination system. Then the growth curve, motility agglutination, biofilm formation and pathogenicity were determined for mutant strain, wild-type strain and complementary strain. This study shows that this gene mutant can enhance the mobility and weaken aggregation capabilities, biofilm-formation ability, and the ability to survive in vivo pathogenicity. But it has no affect on the growth rate, environmental tolerance and adhesion ability invasion.Prevention is always important than cure, so efficient and safe vaccine will be very urgent. We have known that APEC has so many different serotypes. Therefore developed different multivalent vaccine for different regions main serotype is a good choice. Our previous studies show that the mainly serum of APEC were 01,02,078 type and serum 078 type accounts for about 64% in Jiangsu Province, Anhui Province and other surrounding areas. That’s why we focus on serum of 078 type inactivated vaccine. The results show that the APCE94 isolates of APEC 078 serum type has good protection to homologous with oil emulsion type adjuvant. 10-day-old ducklings immunized by APCE94 inactivated vaccine with 5×10 CFU only one time can provide at least 90% rate protection from homologous serotype, titer can reach 1: 400.24-day-old ducklings strengthen the immune can completely free from the invasion of the homologous virulent strain, and the titer can reach 1:1600. Unfortunately, this vaccine can not provide cross-protection to 01,02 serotype infection. |
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