Chickens, Chlorine and Campylobacter: New insights into the redox biology of the most prevalent food-borne pathogen

Some bacteria get into the food that we eat and cause food-poisoning. Some of these bacteria are quite common but are usually killed during cooking. When chicken meat is not cooked properly, one of these types of bacteria, called Campylobacter jejuni, is a particular problem. It normally lives harmlessly in the intestines of chickens but in humans causes severe diarrohea, which although not usually life-threatening, causes considerable impacts on time off work and in some cases can lead to serious complications. By understanding in detail the way in which this bacterium interacts with its hosts and survives in the food-chain we may be able to stop colonisation or improve killing of the bacteria before human ingestion. We are interested in a specific property of C. jejuni that we think is a vulnerability that can be exploited - it is very sensitive to oxygen and is easily killed by "reactive" oxygen and chlorine species like peroxides and hypochlorite. However, we don't fully understand how this occurs. In this project we will be investigating the effects of hypochlorite on proteins and how this damage is repaired. We will also study how gene expression is changed when the bacteria are exposed to hypochlorite and try to find out how they can "sense" the presence of this chemical. The results should allow us to get a better knowledge of the way in which the bacterium responds to oxidative damage, which could be exploited in future to improve food-chain interventions and to inform policy decisions about the use of such treatments.

Campylobacter jejuni is by far the commonest cause of food-borne gastroenteritis in the UK, mainly arising from under-cooked chicken. Research on both the molecular basis of host colonisation and the factors affecting survival in the food-chain is required to inform the rational design of strategies to control this zoonotic pathogen from farm to fork. C. jejuni is an oxygen sensitive microaerophile and this might represent a vulnerability that can be exploited in control measures. Our work has shown that, compared to conventional aerobes, C. jejuni is unique in utilizing oxidant-labile enzymes in central metabolic pathways, which are critical for growth and that allelic variation in specific genes involved in oxygen metabolism and oxidative stress affects survival of C. jejuni strains through the food-chain from chickens to humans. Controversial oxidant based interventions such as carcass-washing in chlorinated water are already being used to control food-chain contamination but their effects are not well understood. Reactive oxygen and chlorine species (ROS and RCS) oxidize Met and Cys in proteins and our preliminary work has shown periplasmic proteins are particularly vulnerable. In this proposed project, we will define the RCS transcriptional response, investigate the mechanisms by which C. jejuni senses RCS, identify those proteins that are most sensitive to oxidation and show how C. jejuni defends itself against RCS damage, using cutting-edge proteomics analyses employing high-resolution mass spectrometry combined with mutant studies and biochemical analysis of protein function. We will also carry out adaptive evolution studies in chemostat culture combined with genome sequencing, to identify genome-wide changes that determine increased resistance to RCS challenge. The proposed project has implications for informing policy on food-chain intervention strategies, the improvement of existing control measures, and the design of new interventions.

1. Who will benefit from the research?
The results from the proposed research project will contribute to knowledge-led approaches for improved food safety in the UK and will also inform policy priorities of the BBSRC, DEFRA and FSA with the aim of reducing food-chain contamination with food borne pathogens. The work also has the longer term potential to impact on success of the poultry industry in the UK. It therefore falls within the remit of the BBSRC Sustainable Agriculture Strategy and priority for research on Global Food Security. The project matches the BBSRC strategic/scientific priorities of 'data driven biology', 'healthy and safe food' and 'Animal Health'.

2. How will they benefit?
The UK poultry industry faces numerous challenges in order to remain sustainable. These include the move to more extensive rearing systems; the withdrawal of prophylactic and many therapeutic antibiotics, and other drugs such as anti-coccidials. These challenges will all have an impact on poultry health, but also have the potential to impact on human health. This proposal will shed light on the mechanisms by which reactive chlorine treatments affect Campylobacter biology that is directly relevant to both its survival in the food chain as well as avian and mammalian colonization. Our research has identified specific repair systems for oxidized proteins that, for example, could constitute a future new target for disruption by small molecule antagonists designed to weaken the ability of C. jejuni to survive in the food chain or colonise the avian or mammalian intestine.