Escherichia coli ghosts or live E. coli expressing the ferri-siderophore receptors FepA, FhuE, IroN and IutA do not protect broiler chickens against avian pathogenic E. coli (APEC)

The aim of this study was to investigate if immunization with the ferri-siderophore receptors FepA, FhuE, IroN and IutA could protect chickens against avian pathogenic Escherichia coli (APEC) infection. The antigens were administered as recombinant proteins in the outer membrane (OM) of E. coli strain BL21 Star DE3. In a first immunization experiment, live E. coli expressing all 4 recombinant ferri-siderophore receptors (BL21L) were given intranasally. In a second immunization experiment, a mixture of E. coli ghosts containing recombinant FepA and IutA and ghosts containing recombinant FhuE and IroN was evaluated. For both experiments non-recombinant counterparts of the tentative vaccines were administered as placebo. At the time of challenge, the IgG antibody response for BL21L and a mixture of E. coli ghosts containing recombinant FepA and IutA and ghosts containing recombinant FhuE and IroN was significantly higher in all immunized groups as compared to the negative control groups (LB or PBS) confirming successful immunization. Although neither of the tentative vaccines could prevent lesions and mortality upon APEC infection, immunization with bacterial ghosts resulted in a decrease in mortality from 50% (PBS) to 31% (non-recombinant ghosts) or 20% (recombinant ghosts) and these differences were not found to be significant.