Disparity in susceptibility to vancomycin-resistant Enterococcus organ invasion in commercial broiler chickens that differ in innate immune responsiveness

Abstract

Enterococci, gram-positive bacterium, are found on virtually all consumer-ready retail meats. Recently, we characterized the innate immune response phenotype of parental lines of broilers (A and B) and F1 reciprocal crosses (C and D). In vitro heterophil functional analyses and in vivo challenge trials showed line A was more immunologically responsive and more resistant to Salmonella (Gram-negative bacteria) and Eimeria tenella (parasitic protozoan) infections than line B. Further, cross D was more responsive with increased resistance compared to cross C. We hypothesized that line A and D chickens were also more resistant to gram-positive bacteria. Day-old chickens were challenged with vancomycin-resistant Enterococcus gallinarum (VREG), euthanized, and hearts, livers, and spleens cultured for VREG. One-day post challenge, there were significantly fewer VREG-positive hearts, livers, and spleens in line A than line B. Likewise, cross D chickens had significantly fewer VREG-positive hearts, livers, and spleens than cross C chickens. To determine if VREG was cleared, chickens were necropsied seven days post-challenge. Again, significantly fewer organ cultures from line A and D were VREG-positive compared to line B and C. Further, this study showed the hematologic profile reflected changes associated with protection against VREG; there were significantly more circulating heterophils and monocytes in VREG-resistant lines A and D with no changes in VREG-susceptible lines B and C. Collectively, line A and D chickens are immunologically more responsive and more resistant to pathogens, including VREG, compared to line B and C chickens.