Immunization of chickens with live Escherichia coli expressing Eimeria acervulina merozoite recombinant antigen induces partial protection against coccidiosis.

Inoculation of chickens with live Escherichia coli N6405 transformants containing a plasmid which encodes ampicillin resistance and an immunodominant p250 surface antigen of Eimeria acervulina merozoites induced partial protection against challenge with live coccidia. The inoculation with E. coli transformants induced antigen-specific immunoglobulin and cell-mediated immune responses. Challenge with infective oocysts of Eimeria acervulina enhanced both immune parameters, indicating that administration of live E. coli transformants served to prime the immune system for recognition of specific epitopes on the 250-kilodalton protein. Although the mechanism of antigen presentation is unclear, the data suggest that in vivo expression of recombinant merozoite antigen is operative. After administration, no E. coli N6405 transformants could be recovered from intestinal or fecal materials of inoculated chickens, as assessed by enumeration on selective medium. However, ampicillin-resistant E. coli originating from the normal flora and harboring the gene sequences for both antibiotic resistance and Eimeria acervulina merozoite surface protein could be recovered from these chickens. Furthermore, normal-flora E. coli transformants were capable of generating functional beta-lactamase product, as evidenced by their resistance to ampicillin, and immunoreactive E. acervulina merozoite recombinant antigen, as revealed by immunofluorescence staining with p250-specific antiserum.