Campylobacter jejuni, commonly associated with poultry, causes human campylobacteriosis. Hung-Yueh Yeh, Kelli Hiett, J. Eric Line and Bruce Seal of the USDA Richard B. Russell Agricultural Research Center at Athens, Georgia explain in their report that although many strategies for reducing C. jejuni contamination in poultry have been examined, there are currently no practical intervention means available for the poultry industry to effectively reduce the contamination of C. jejuni during production and processing. Therefore, research for practical on-farm interventions is an urgent need.

In this proposal for the US Poultry and Egg Association, the group approached this problem by development of C. jejuni sub-unit proteins as potential vaccines for broilers.

The hypothesis of the proposed study was that expression of a battery of C. jejuni proteins involved in colonisation has the potential for discovery of novel antigen(s) that can be used for in-ovo vaccination to reduce the bacterium in broiler chicken gastrointestinal systems.

The specific objectives of this proposal were to

1. construct a system for expressing large amounts of important C. jejuni proteins
2. produce and purify the recombinant C. jejuni proteins
3. assay the immune response in broiler chickens against these C. jejuni proteins, and
4. conduct vaccination experiments with the C. jejuni proteins.

Objective 1

Fifty-seven C. jejuni genes potentially involved in colonisation were identified. Twenty-eight genes were successfully over-expressed to allow purification of proteins.

Objective 2

The proteins were purified using chromatography.

Objective 3

Two recombinant proteins - flagellar capping protein (FliD) and methyl-accepting chemotaxis protein (Cjj0473) reacted strongly to sera from broilers older than six weeks of age in the preliminary experiments, indicating that these were antigens which the broiler immune system was exposed to and responding to in the field.

Next, the researchers evaluated whether sera collected from other areas in the US contained antibodies against the FliD protein. Sera from layer breeders at 44 to 52 weeks of age showed 100 per cent positive, while sera from broilers at four to six weeks of age from 22 premises showed seven to 100 per cent positives.

These results suggest that C. jejuni was widespread in these poultry populations, and chickens had been exposed to this microorganism. It appears that prevalence of C. jejuni in these poultry populations was age-related.

Objective 4

Three in-ovo experiments were conducted. The results showed very poor hatchability, suggesting that the adjuvant used was toxic to chicken embryos. Next, one-day-old maternal antibody-positive broiler chickens were vaccinated with 100mg per chicken of the FliD protein prepared with an equal amount of incomplete Freund's adjuvant. The broiler chicks responded by producing antibody to the protein.

These results suggest that the FliD protein is immunogenic in broilers and that this protein has potential as a vaccine candidate. The results also indicate that maternal antibodies may not affect immunisation.

Conclusions

Yeh and colleagues conclude their results have following potential impacts for the industry.

They found that this protein is present in all 21 C. jejuni isolates and is immunogenic in broilers. Therefore, this protein will be an excellent candidate for further evaluation as a vaccine to reduce Campylobacter in poultry.

In addition, antibodies to this protein may be used for as a tool to monitor the Campylobacter status during poultry production. Currently, C. jejuni is regarded as a commensal in the chicken gut intestine, which does not harm chickens. The Athens studies, however, demonstrated that broiler sera reacted to a variety of Campylobacter proteins, suggesting that chickens had been exposed to or infected with this microorganism, and consequently developed antibodies against it.

Further, they showed antibodies against the FliD protein were widespread in poultry populations. Therefore, control of Campylobacter exposure through vaccination of chickens is a logical approach to Campylobacter control, and the FliD protein is a good vaccine candidate.

Further studies must be done to evaluate the use of this protein by in-ovo application to determine its potential practical use and efficacy, added Yeh and colleagues.

July 2014