Use of a modified bacterial ghost lysis system for the construction of an inactivated avian pathogenic Escherichia coil vaccine candidate

Vaccination is an effective strategy to prevent avian colibacillosis. Bacterial ghosts (BGs) are prepared by the controlled expression of the phiX174 gene E, which mediates the lysis of Gram-negative bacteria. Staphylococcal nuclease A may be used to produce BGs for further inactivation of host bacteria and elimination of residual genetic material. In this study, the double promoter lysis plasmid (pUC19-Delta c1857-E-rmB-A-SN) was successfully constructed and BGs were prepared at 37 degrees C. The cleavage efficiency of Escherichia coil BGs was 99.9%. Furthermore, to evaluate the immunological effects of the BG vaccines in chickens, a BG vaccine was prepared using the serotype O-2 avian pathogenic Escherichia coil deletion strain (DE17 Delta luxS Delta aroA). The results showed that the BC vaccine was able to achieve over 90% immune protection against virulent challenge using the same serotype O-2 strain (DE17 or CE35), while it showed poor cross-protection against serotypes O-1 and 078 (data not shown). The enzyme-linked immunosorbent assay results showed that the antibody levels in the immunized groups were higher than in the control group (p < 0.05), with the BG group being the highest. The cytokine tests showed that the levels of interferon-gamma in the BG immune group were higher than in the phosphate-buffered saline (PBS) control group (non-immune) (p < 0.01) and the formalin-inactivated vaccine immune group (p < 0.05), and the levels of tumor necrosis factor-alpha in the BG group were higher than in the formalin-inactivated vaccine (p > 0.05) and the PBS control groups (p < 0.05). In addition, pathological analysis revealed that the PBS control group showed typical fibrinous pericarditis and perihepatitis, whereas the immune group showed no obvious pathological changes. In summary, our findings provide a new strategy for the prevention and control of avian colibacillosis.