Pathogen surface characteristics and transport through catchments

Executive summary The passage of enteropathogenic bacteria from agricultural land to fresh and marine water supplies represents a major source of environmental pollution and risk to human health. However, the factors that regulate pathogen flow from soil to freshwater remain poorly understood. Similarly, hydrological models that may be capable of predicting pathogen flow at the landscape scale remain to be validated. This PhD studentship will directly address these issues. The hypothesis to be tested During storm events, pathogenic E. coli from livestock faeces are washed over or through soil and into water courses. Predicted numbers of E. coli found in water courses often fail to match those predicted by modelling studies. We hypothesize that this is due to attachment of the bacteria to soil or stream sediment particles. We predict that during storm events and concomitant high water flows, these 'trapped' bacteria get flushed back into the stream, giving rise to higher numbers than would be expected from those washed off the land (from the mixing of run-off water and faeces). Presence of generic E. coli indicates that potentially pathogenic bacteria may also be present (e.g. E. coli O157:H7). However, direct comparison of the environmental behaviour of pathogenic and non-pathogenic E. coli remains largely untested hampering the acceptability of models to predict pathogen flow derived from non-pathogenic E. coli data. Our second hypothesis is therefore that there is a fundamental difference between these two E. coli groups due to known molecular differences in their effacement mechanisms. Furthering our mechanistic understanding of how pathogenic and non-pathogenic E. coli attach to different particles and what factors influence their attachment and release will greatly enhance our capability to predict their flow in the environment. To achieve this, we will initially examine the surface characteristics of both the particles and the bacteria and then investigate key environmental variables which may influence E. coli attachment and detachment (e.g. mechanical stress, turbidity, temperature, C supply, competition, water quality/salinity). Following on from this, we will monitor numbers of E. coli in real soils and associated streams in livestock areas to validate the laboratory studies. Lastly, the student will work directly with hydrological modelers at the Macaulay Institute to improve existing model describing pathogen flow and validate component parts of these using the experimental data.