The assessment of coli index with E. coli immunosensor in natural water

The bathing water microbiological quality is commonly assessed by cultivation. Microbiological cultivation is the “gold standard” for water quality assessment, but the results take several days. Alternatives, such as the qPCR method, allow bacteria to be enumerated more efficiently but are yet laborious and require the transportation of samples and complex instrumentation. For the automated in situ monitoring of water quality, E. coli immunosensors have great potential for replacing the lab-based methods mentioned above. However, interpreting E. coli immunosensor response can be complicated as all antigens that interact with the antibody used for bio-recognition potentially generate a measurable signal. These antigens can be live, dead, or fragmented cells of E. coli, but also different coliforms present in the environment. In the present study, we identified which bacteria and at what degree of cell degradation are causing the measurable signal of E. coli immunosensor in natural bathing waters. It was found that the live cultivable E. coli bacteria caused only ~ 10% of the measured immunosensor output. At the same time, most of the signal was generated by non-cultivable E. coli and its fragments along with different coliforms.