A Completely Automatic Optical Biosensor System for Stressed Bacteria in Marine Water

Laboratory techniques used for the quantification of pathogenic and environmental bacteria commonly give results within 18-72 h after sampling. In some cases, as for bathing waters quality control, the time needed for results can represent a not negligible problem, since microbial contamination can be confirmed when public health has been already jeopardized. To overcome this problem, in the absence of analytical methods faster than those approved by law, cutting-edge technologies can offer today a plethora of innovative solutions. Recent developments in electronic engineering, for instance, have led to the miniaturisation of detectors, giving the possibility of designing analytical instruments with features of higher detection power, smaller size and better portability. Biosensors, in this context, are among the instruments that mostly exploit miniaturized technology, thus enabling easy and rapid analysis directly on site, as required for biomedical or environmental analysis. The advantage of using biosensors is that the analytical procedure leading to target's identification is usually highly specific and reduced to few, extremely simplified steps, not requiring specialized personnel. On this basis, we developed a novel, completely automatic optical biosensor system able to rapidly detect faecal bacteria in marine water. The developed system (patent pending) is able to autonomously perform the entire analytical procedure usually followed in a microbiological laboratory, from sample incubation in culture medium to the analysis itself. The autonomy is guaranteed by the provision of a standalone supply box, including battery, solar panels, substrate stock and a communication system that constantly interacts, by the Universal Mobile Telecommunications System (UMTS) network, with a web server application storing and showing data. The principle of the analysis is based on the hydrolysis of the substrate ?-D-glucuronide contained in the culture medium added to the sample. The hydrolysis, operated by the enzyme ?-D-glucuronidase (a specific marker for E. coli), leads to 4-methylumbelliferone, the fluorescence of which is measured, thus giving evidence of the presence of E. coli, assumed as an indicator of faecal contamination. In order to validate the system, results were obtained in parallel with those gained with a standard fluorogenic substrate method; the microbial growth was quantified on this latter medium. The developed biosensor system reliably detected E. coli as low as 1 cfu/mL of marine water sample. This study paves the way to the development of an automatic monitoring platform, remotely controllable, intended for the management and control of water resources (seas, rivers, lakes) and able to act as an early warning system launching alarm signals when fixed threshold values of pathogens are exceeded.