In Situ Detection of the Pathogen Indicator E. coli Using Active Laser-Induced Fluorescence Imaging and Defined Substrate Conversion

To remotely sense the pathogen indicator E. coli in aquatic systems, we used laser-induced fluorescence imaging to detect the signature produced by the in situ conversion of the defined substrate medium ECMUG. The presence of the enzyme β-glucuronidase, indicated by the activity of the fluorogenic 4-methylumbelliferyl (4MU)-β-D-glucuronide (MUG), is specific to the presence of this organism. Substrate conversion was accomplished in a small stream impacted by non-point source wastewater inputs. Sample chambers slowly inoculated source water with 100 ml of ECMUG media in direct sunlight. Luminescence spectroscopy monitored conversion activity and detected liberation of the 4 MU fluorochrome in 2.5 hours. Detection by laser-induced fluorescence imaging followed at dusk and indicated bright blue emissions typical for converted media. This technique lays the foundation for active remote sensing of source water contamination.