Development of a Rapid, Sensitive and Reliable Test for the Detection and Quantification of Escherichia coli in Foods

The goal of this project is to develop a rapid and sensitive, yet simple and reliable test for the identification and quantification of E. coli in foods.
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The test is a modified version of the standard E. coli test where a sample is incubated for up to 24 hours in a solution containing a fluorogenic substrate. E. coli bacteria in the sample will grow and produce the enzyme - glucuronidase, which then hydrolyzes the substrate to produce a fluorescent product. The new fiber-optic test system uses a custom designed substrate compound and a fiber-optic probe designed to detect the unique product generated when E. coli consumes the substrate. A prototype commercial instrument has been constructed, consisting of a portable, computer controlled electro-optics unit and a small heated sample compartment.
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Fluorescence is continually monitored, providing the earliest possible indication of a positive sample. Human judgment of the fluorescence is not required, and the probe can extract the optical signal even from coloured and turbid samples. In addition, by tracking the fluorescence signal over time, an estimate of the number of cells present in the initial sample can be made, providing a quantitative test. The method has been confirmed in milk and juice, and for vegetable washes which gave an 'overgrown' result with conventional membrane filter tests. Highly contaminated samples can be confirmed positive in as little as 1-2 hours.