Submitted to: Food and Agricultural Immunology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2004
Publication Date: 3/1/2005
Citation: Swaggerty, C.L., Lowry, V.K., Ferro, P.J., Pevzner, I.Y., Kogut, M.H. 2005. Disparity in susceptibility to vancomycin-resistant Enterococcus organ invasion in commercial broiler chickens that differ in innate immune responsiveness. Food and Agricultural Immunology. 16:1-15. Interpretive Summary: Enterococci are germs that can cause serious infections in people. Often, these infections are obtained when the person is in the hospital. The problem with enterococcal infections is that these germs are resistant to most antibiotics, including vancomycin. From a food-safety perspective, this is important because enterococci are found on virtually all raw chicken products that are purchased in the United States. Recently, we have been working with two parental lines of chickens (A and B) and their crossbred offspring lines (C and D) to find out why lines A and D are more resistant to infections, including Salmonella. Chickens have cells in their blood called heterophils and we found that heterophils in line A and D chickens function better than heterophils from line B and C chickens. Since line A and D chickens are more resistant to Salmonella infections and have better heterophils, we wanted to know if these chickens were also more resistant to enterococcal infections. For this study, baby chicks were challenged with vancomycin-resistant Enterococcus gallinarum (VREG). After 1- and 7-days post challenge, we looked for VREG in these chicks. At both time-points, there were significantly fewer VREG-positive chicks in line A than line B. Likewise, there were significantly fewer VREG-positive crossbred D chicks compared to crossbred C chicks. We also collected blood from VREG-resistant chicks (A and D) and found more heterophils in their blood compared to VREG-susceptible chicks (B and C). Taken together, parental line A and crossbred D chickens have a better immune response and are more resistant to infections, including VREG and Salmonella, compared to parental line B and crossbred C chickens. This is important because if resistant chickens are used in the market, the meat from these chickens is more likely to be uncontaminated by pathogens and thus will be more safe to eat.
Technical Abstract: Enterococci are Gram-positive causative agents of nosocomial infections possessing high resistant to antimicrobial agents and are found on virtually all consumer-ready chicken. Recently, we characterized the innate immune response phenotype of two parental lines of broilers (A and B) and F1 reciprocal crosses (C=A hen × B rooster; D=A rooster × B hen). In vitro heterophil functional analyses and in vivo challenge trials showed line A chickens were more immunologically responsive and more resistant to Salmonella (Gram-negative bacteria) and Eimeria tenella (parasitic protozoan) infections than line B. Further, cross D chickens were more responsive with increased resistance compared to cross C chickens. Therefore, we hypothesized line A and D chickens would also be more resistant to Gram-positive bacteria. For this study, day-old chickens were challenged with Vancomycin-resistant Enterococcus gallinarum (VREG), euthanized one- and seven-days post-challenge, 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 7 days post-challenge. Significantly fewer organ cultures from line A were VREG-positive than line B. Additionally, fewer organ cultures were VREG-positive from cross D chickens compared to cross C. Finally, we wanted to determine if the hematologic profile reflected changes associated with protection against VREG. There were significant increases in circulating heterophils and monocytes in VREG-resistant lines A and D but no changes in VREG-susceptible lines B and C. Taken together, parental line A and cross D chickens are immunologically more responsive and more resistant to pathogens, including VREG, compared to parental line B and cross C chickens.