Immunogenicity of live phoP gene deletion strain of Riemerella anatipestifer serotype 1

Duck infectious serositis is an acute and infectious disease caused by Riemerella anatipestifer (R. anatipestifer) that leads to perihepatitis, pericar-ditis, meningitis, and airbag inflammation in ducks, which causes serious economic losses to the global duck industry. The phoP/phoR is a novel 2-component signal transduction system first reported in gram-negative bac-teria, of which phoP acts as a global regulator and viru-lence factor. In this study, the phoP gene from the R. anatipestifer YM strain was knocked out using homolo-gous recombination technology and replaced with the spectinomycin resistance gene (Spec). The virulence of the R. anatipestifer YMAphoP strain was reduced by approximately 47,000 times compared to that of the wild-type R. anatipestifer YM strain. Ducks were immu-nized with live R. anatipestifer YMAphoP strain by sub-cutaneous inoculation at a dose of 106 to 107 CFU (0.2 mL per duck) and challenged with the wild-type R. anatipestifer YM strain 14 days later. The protection rate in the immunized group was 100%. The growth characteristics of ducks in the immunized and negative control groups were normal, and the research demon-strated R. anatipestifer YMAphoP strain have suitable immunogenicity and protective effects. Thus, the study findings suggest that the novel R. anatipestifer YMA- phoP strain may provide a candidate for the develop-ment of a gene deletion activated vaccine against duck infectious serositis.