Real-time inference of thermotolerant coliforms in groundwater

Enteric pathogens are typically inferred from the presence of cultured surrogate indicator organisms such as thermotolerant coliforms (TTCs). Their analysis requires suitable laboratories, specialist trained personnel, and is time-consuming, which can limit sampling resolution, particularly during critical pollution events. Tryptophan-like fluorescence has been demonstrated as a useful indicator of human influence on freshwater resources due to its association with sewage and farm waste. Following recent developments in field-deployable optical sensor technology, portable tryptophan-like fluorimeters are now commercially available. We demonstrate their real-time applicability at potable urban groundwater supplies in the developing world. We sampled over 100 supplies for TTCs, and traditional surrogates, such as turbidity and nutrients, as well as tryptophan-like fluorescence. The intensity of tryptophan-like fluorescence was the most effective predictor of the presence/absence and number of TTCs. These sensors have the potential to be included in real-time pollution alert systems for drinking water supplies throughout the world, as well as mapping enteric pathogen risks in developing regions.