Photon based sensing of pathogens in food

A chemiluminescence assay for detection of coliforms was developed based on reaction of β-galactosidase enzyme from Escherichia coli with a phenylgalactosidase-substituted dioxetane substrate, leading to generation of light at 530 nm. An antibiotic is added to increase cell membrane permeability. Upon addition of the dioxetane substrate, the stable dioxetane is enzymatically deprotected by β-galactosidase to produce an unstable form of dioxetane, which decomposes in a local hydrophobic environment producing a singlet-excited ester. Photons are generated when the excited ester decays and energy transfers to a fluorescing chemical present in the dioxetane substrate cocktail. Light emitted from the reaction is measured,in a commercial luminometer. Photon count is correlated with number of E. coli cells enumerated on agar plates. An exponential increase in the intensity of light emitted is observed with exponential increase in numbers of E. coli. The detection limit for the assay is 10²-10³ cells in 45 min. Enzyme-based chemiluminescence sensing provides a simple and rapid method for detection of microbial contamination in foods.