A new, short term, sensitive, bacterial assay kit for the detection of toxicants

We present and evaluate a new bacterial test suitable for the detection of toxicants in water, chemicals, pharmaceuticals, foodstuff, food additives and cosmetics. It is a simple, rapid (1–1.5 hours), colorimetric assay which does not require special equipment, and can easily be carried out under field conditions. The assay is based on the ability of toxicants to inhibit the de novo synthesis of an inducible enzyme, e.g., β-galactosidase, by a rough mutant of E. coli, which is highly sensitive to a wide spectrum of toxic substances, such as pesticides, mycotoxins and heavy metals. The test is performed under stress conditions for the bacterium, since under such conditions better sensitivity for low concentrations of analytes is obtained. In the assay, serial dilutions of the sample are mixed with the stressed bacteria and a cocktail containing the specific inducer for the chromogenic enzyme and essential factors, required for the recovery of the bacteria from their-stressed condition. The ability of cells to synthesize β-galactosidase under these conditions depends on their ability to recover from the stress. Toxic materials interfere and/or inhibit the recovery process and with it the synthesis of β-galactosidase. The amount of the de novo synthesized enzyme is determined by a colorimetric reaction. We have developed a commercial kit based on the assay. The kit is field oriented and easy to operate. The kit contains the bacteria in a lyophilized form and all the reagents have been stabilized so that the kit may be stored under normal refrigeration for a long period of time.