2004 - 2006

Identification of gut bacteria affected by dietary antibiotics and their roles in the gut immunity of broiler chickens

Principal Investigator: Joshua Gong, Agriculture and Agri-Food Canada; Shayan Sharif, University of Guelph
Co-investigator: Huaijan Zhou, Texas A&M University; Parvis Sabour, Agriculture and Agri-Food Canada; Babek Sanei, Ontario Ministry of Agriculture, Food and Rural Affairs; Jennifer Brisbin, University of Guelph (PhD candidate)
Status: Completed


There are increasing concerns over the development of bacterial resistance to antibiotics. While it is not clear if the use of antibiotics to prevent infection and promote growth in poultry is a contributing factor, it is clear that antibiotics do have an effect on microbial populations in the chicken gut. It has also been shown that antibiotic use affects development of the chicken’s immune system. The objectives of this research project, therefore, were to determine which microbes in the gut are most affected by antibiotics and to determine how these microbial changes affect the immune system.

Research Progress

An experiment was set up in which birds were fed either non-medicated diets or those supplemented with bacitracin (4.4 or 55 ppm) or virginiamycin (11 or 22 ppm). Samples were taken from various regions of the gut at 3, 7, and 14 days and microbial populations were compared. Genetic analysis revealed that many bacterial groups were affected by the presence of the antibiotics used in this study. Effects were most pronounced with virginiamycin. This antibiotic was then used in a trial during which birds fed medicated or non-medicated feed were immunized with several potent antigens designed to elicit an immune response. In most cases, the presence of virginiamycin in the feed did not affect the immune response of the birds, but there were a few specific cases for which immune response was increased. This result is surprising and may provide some insight as to why subtherapeutic levels of antibiotics can improve broiler chicken performance. Several species of Lactobacillus bacteria were affected by the presence of virginiamycin in this study. Lactobacilus acidophilus has been linked to increased immune response in chickens. Components of this bacterium were therefore used to stimulate chicken immune system cells in the laboratory. The cells responded by increasing expression of several genes relating to immune function. It has been hypothesized that a decreased population of L. acidophilus in the gut due to antibiotic use could have a negative effect on immune function in the bird. Results from this research project suggest, however, that the use of antibiotics such as virginiamycin does not negatively affect immune function in broiler chickens.

Future Work

Work is ongoing to further characterize changes in immune system gene expression in response to antibiotics. This information will be crucial to finding ways to improve the chicken’s immune function, both to enhance the effectiveness of currently antibiotics and to perhaps reduce the need for them in the future.


$260,000 (CPRC $100,000, PIC $30,000, MII $55,000, NSERC $75,000)


Zhou, H., Gong, J., Brisbin, J., Yu, H., Sanei, B., Sabour, P., and Sharif, S. 2007. Appropriate chicken sample size for identifying the composition of broiler intestinal microbiota affected by dietary antibiotics using the PCR-DGGE technique. Poult. Sci. 86:2541-2549 Brisbin, J.T., Zhou, H., Gong, J., Sabour, P.M., Akbari, M.R., Haghighi, H.R., Yu, H., Clarke, A., Sarson, A.J., and Sharif, S. 2008. Gene expression profiling of chicken lymphoid cells after treatment with Lactobacillus acidophilus cellular components. Dev. Comp. Immunol. 32:563-574 Brisbin, J.T., Gong, J., and Sharif, S. 2008. Interactions between commensal bacteria and the gut-associated immune system of the chicken (Review Article). Anim. Health Res. Rev. (in press) Brisbin, J.T., Gong, J., Lusty, C.A., Sabour, P., Sanei, B., Shewen, P.E., Sharif, S. Influence of in-feed virginiamycin on the systemic and mucosal antibody response of chickens (submitted to Poultry Science)

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