Direct detection of E. Coli O157:H7 in selected food systems by a surface plasmon resonance biosensor

The Spreeta^TM, surface plasmon resonance (SPR)-based biosensor, was used to detect Escherichia coli O157:H7 spiked in milk, apple juice and ground beef extract using specific antibodies. In the Spreeta^TM biosensor light from an LED is reflected off a gold surface, and the angle and intensity corresponding to the SPR minimum is measured and represented as a refractive index (RI) change corresponding to the antigen-antibody coupling at the sensor surface. Milk, apple juice, and ground beef patties spiked with E. coli O157:H7, at varying concentrations, were injected on the sensor surface immobilized with antibodies against the pathogen at a rate of 1 ml/min for a total of 2 min. The change in RI due to the binding of O157:H7 corresponding to each concentration was computed as an average of three replications over a 2 min interaction period. Assays were conducted at near real-time and results obtained after about 30 min of sample injection. Sensitivity of the E. coli O157:H7 assay was 10²-10³ colony forming unit (CFU)/ml. The biosensor assay was also specific to E. coli O157:H7 as other organisms (E. coli K12 and Shigella) did not produce any appreciable change in the sensogram. Further experiments are needed to establish well-defined methods for detecting other food-borne pathogens in more complex and specific food matrices.