An official website of the United States government.
This project addresses the priority area "Prevention and Control of Salmonella and Campylobacter in Poultry Flocks" by developing a vaccine composed of a Salmonella vector expressing Campylobacter proteins to reduce Campylobacter loads in chickens. We have identified three putative virulence genes from C. jejuni encoding novel proteins from the outer-membrane of the bacterium. Two of the genes when expressed in the attenuated Salmonella vector, and used in oral vaccine studies significantly reduced the ability of C. jejuni to colonize chicks. Additionally, a third gene when mutated, essentially eliminated the ability of the mutant strain to colonize chicks. <P>Objectives include 1) cloning this third gene into the Salmonella vector to test in vaccine trials, 2) examining a 2 and 3 way component vaccine to determine if a combination of multiple expressed proteins will further reduce the Campylobacter load in broilers, and assembling the genes into a single commercially viable Salmonella vector, 3) examining optimal vaccination delivery methods, 4) evaluating the immune response of vaccinated poultry, and 5) translating the efficacy and cost-effectiveness of risk-based interventions for reducing Campylobacter loads to the poultry industry through integrated extension and outreach activities. Vaccinations with combinations of two or three of these genes should significantly reduce (>3 logs) or eliminate C. jejuni from broiler chickens. Successful vaccination of chickens would lead to compliance of the new FSIS performance standards for Campylobacter by improving the safety of poultry, thereby significantly preventing campylobacteriosis.
Non-Technical Summary:<br/>
Campylobacteriosis is a food-borne disease, with the handling and consumption of poultry considered the most significant risk factor in transmission. Campylobacteriosis costs the U.S. economy in excess of $3 billion annually. Due to the emergence and persistence of antibiotic resistance, coupled with increasing regulatory restrictions on the poultry industry, control strategies such as vaccination are urgently needed. Vaccination studies with C. jejuni have been highly variable, primarily due to the fact that C. jejuni colonizes poultry without the production of disease. The most promising results to date have been achieved using attenuated Salmonella vectors to express and deliver C. jejuni antigens to the intestinal mucosa of broilers. This project proposes to develop a vaccine composed of a Salmonella vector expressing Campylobacter proteins to reduce Campylobacter loads in chickens. Currently, no intervention method or vaccine is available to the producer to effectively reduce numbers of Campylobacter from poultry going to processing. The principal investigator and collaborators have extensive experience in the study of Campylobacter pathogenesis, Salmonella vectors, vaccine development, risk-based modeling, and performing outreach activities. Preliminary data predicts the outcome of an effective vaccine to reduce C. jejuni in poultry. We have identified three putative virulence genes from C. jejuni encoding novel proteins from the outer-membrane of the bacterium. Two of the genes when expressed in the attenuated Salmonella vector, and used in oral vaccine studies significantly reduced the ability of C. jejuni to colonize chicks. Additionally, a third gene when mutated, essentially eliminated the ability of the mutant strain to colonize chicks. Specific aims include cloning this gene into the Salmonella vector to test in vaccine trials, examining a 2 and 3 way component vaccine to determine if a combination of multiple expressed proteins will further reduce the Campylobacter load in broilers, assembling the genes into a single commercially viable Salmonella vector, examining vaccination methods, evaluating the immune response of vaccinated poultry, and translating the efficacy and cost-effectiveness of risk-based interventions for reducing Campylobacter loads to the poultry industry through integrated extension and outreach activities. Vaccinations with combinations of two or three of these genes should significantly reduce (>3 logs) or eliminate C. jejuni from broiler chickens. Successful vaccination of chickens would lead to compliance of the new FSIS performance standards for Campylobacter by improving the safety of poultry, thereby significantly preventing campylobacteriosis. Extension efforts including combining industry-wide surveys, mathematical risk-based models, and diverse extension and outreach activities will enable us to synthesize information about targeted risk-based interventions for Campylobacter reduction, including the use of our vaccine. The development of an efficacious vaccine to reduce the Campylobacter load in chickens would be an innovative breakthrough for the control of this significant food-borne disease.
<P>
Approach:<br/>
The difficulty in developing a vaccine is because C. jejuni colonizes the intestinal tract of poultry as a commensal, and without a live delivery system of the appropriate antigen, it is very difficult to generate a protective intestinal mucosal immune response. Recombinant attenuated Salmonella vaccines have been adapted to stably express protective antigens at high levels. They are capable of stimulating strong primary humoral, mucosal and lasting memory immune responses without significant tissue damage or other performance reducing effects. The Salmonella vector in this study has three deletion mutations that render the vaccine strain avirulent following colonization of the host. We have identified three genes from a membrane extraction of C. jejuni that are conserved among all Campylobacter strains. Two of the genes when expressed in the attenuated Salmonella vector, and used in oral vaccine studies significantly reduced the ability of C. jejuni to colonize chicks. Additionally, one gene when mutated essentially eliminated the ability of the mutant strain to colonize chicks. Poultry colonization has been the major criteria in determining virulence factors in C. jejuni. We will clone this gene into the Salmonella vector to use to vaccinate chicks. A significant reduction in cecal colonization in chicks vaccinated is expected. We will then test 2 and 3 way component vaccines to examine if there is an increase in protection with any of the combinations. If there is an increase, we will assemble the genes for a single commercially viable vector. If there is not, then we will focus on the vector expressing the protein providing the greatest protection, and conduct three vaccinations instead of two, since three vaccinations are currently being used in the industry. We will examine heterologous strains and vaccination procedures, which will require more of an iteration process. The immune response of poultry vaccinated will be examined, to provide a baseline for the immune response generated. Our extension efforts will focus on the translation of risk-based interventions, including the use of our novel Campylobacter vaccine, to the poultry industry. We will first survey stakeholders within the poultry industry, to gather information regarding the interventions that have been tried or proposed for controlling Campylobacter and Salmonella, and specifically, for reaching the cutoffs set in the FSIS performance standards. We will optimize mathematical risk-based models that we have already been developing for the poultry industry, and incorporate into these models the role of vaccination. Finally, we will use the surveys to determine optimal content and delivery platforms for our outreach activities. Significance of results will be statistically evaluated by an epidemiologist, and the extension component will have iterative feedback processes, wherein the surveys will be refined, and the symposia and outreach activities adapted. Meetings with an advisory board will be held to assess the progress and potential impacts of the project, as well as serve as a liaison between government and industry.