Identification and functional analysis of surface factors that enable human pathogens to adhere to and colonise plants.

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Foodborne illness is one of the main burdens of infectious disease in the developed world. Microbes such as viruses, bacteria and parasites are all associated with food and many of them can be found in farm animals, crop plants and water. However, there is an important distinction between those microbes that can use plants or animals as hosts, i.e. are able to proliferate on or within the host, and those that are simply transported through the food chain by them. Just a few bacteria that are foodborne pathogens (including E. coli O157 and Salmonella) account for a large proportion of all foodborne illness, largely because of their extraordinary ability to adapt to a wide range of environments and to proliferate on hosts of any biological kingdom. These pathogens have a strong association with animal hosts, in particular farm animals. From this source, the bacteria can be transmitted into water, by flies or onto growing crops. Although we traditionally associate these bacteria with animal hosts, we have good evidence to show that they can also proliferate on and within plant hosts. This is important because the number of foodborne outbreaks from contaminated fresh produce, in the form of ready-to-eat or minimally processed fruit and vegetables has increased over the past two decades. The increase can only be partly accounted for by better surveillance and detection methods, and there is a possibility that it is also linked to climatic change. Consumption of fresh produce is rightly promoted as part of a healthy life-style, which increases the need to fully understand the basis of colonisation of crop plants by foodborne bacteria. Appreciation of this area is on the rise, although our knowledge of the biological basis to bacteria-plant interactions is in its infancy. Therefore, it is important to build up a solid foundation from which we can make informed decisions that affect food safety practices and government policy. This project aims to determine some of the basic information about how foodborne bacteria colonise crop plants. There are likely to be a large number of genes involved which will fall into different functional families. This project will focus on the genes that encode structures present on the bacterial cell surface, i.e. those most likely to interact directly with plant cells. Preliminary work has already indicated a role for an E. coli O157:H7 adherence factor in bacteria-plant interactions and it will be investigated in much greater detail to fully characterise its role. Structures on the bacteria cell surface seldom work in isolation and when they do, they are extremely tightly controlled to ensure that they are only produced at the most appropriate time. Therefore, additional surface factors of E. coli O157:H7 will be identified, which can then be tested to determine their role in the bacteria-plant interactions. A proportion of the bacterial population are able to enter the internal tissues of plants, where they cannot be removed by conventional sanitation techniques used in food production. Whether any of the bacterial surface factors play a role in bacterial internalisation of plant tissue will also be assessed. The other side of the bacteria-plant relationship will also be examined, to determine whether the plant can sense any of the bacterial surface factors specifically. The approaches used will provide a clearer picture as to the nature of the relationship between plants host and bacteria. The information will contribute to a wider wealth of knowledge, with a common goal to reduce the incidence of foodborne illness.