Recombinant proteins from Gallibacterium anatis induces partial protection against heterologous challenge in egg-laying hens

Gallibacterium anatis is a Gram-negative bacterium and major cause of salpingitis and peritonitis in egg-laying hens, thereby contributing to decreased egg production and increased mortality among the hens. Due to widespread drug resistance and antigenic diversity, novel prophylactic measures are urgently required. The aim of the present study was to evaluate the cross-protective capacity of three recombinant proteins recently identified as potential vaccine candidates; GtxA-N, GtxA-C, and FlfA, in an in vivo challenge model. Nine groups of birds were immunized twice with each protein, respectively, with 14 days separation. Additionally, three groups served as non-immunized controls. After 3 weeks, the birds were challenged with either of three G. anatis strains: 12656-12, 7990 or IPDH 697-78, respectively. Blood samples were taken at three different time points prior to challenge, as well as 48 h after challenge. All birds were euthanized and subjected to a post mortem procedure including scoring of lesions and sampling for bacterial growth. Moreover, ELISA assays were used to quantify antigen-specific IgG titers in serum. The results showed that all three proteins induced protection against the homologous strain 12656-12. No protein induced complete protection against strain 7990, although FlfA reduced the bacterial re-isolation rate. Moreover, immunization with GtxA-N and FlfA induced protection, while GtxA-C reduced the bacterial re-isolation, against strain IPDH 697-78. Thus although complete cross-protection against all three strains was not achieved, the results hold great promise for a new generation of immunogens in the search for novel prophylactic measures against G. anatis.