A group-specific microbiological test for the detection of tetracycline residues in raw milk

The potentiality of using a luminescent Escherichia coli strain for the spe cific detection of tetracycline residues in raw bovine milk was investigate d. The sensor cells contain a reporter plasmid carrying the bacterial lucif erase operon of Photorhabdus luminescens under the control of the tetracycl ine responsive control region from transposon Tn10. Incubation of the cells with the sample containing tetracyclines increases the light emission of t he sensor cells. The most sensitive tetracycline detection was achieved in 120 min and by using CDTA as a chelating agent in the assay. Heat-treatment of milk before the assay decreased the variations in background luminescen ce signals and in tetracycline-induced luminescence between different milk samples. The detection limits for tetracycline, oxytetracycline, chlortetra cycline, doxycycline, methacycline, demeclocycline, and minocycline were be tween 2 and 35 ng/mL. Nontetracycline antibiotics did not significantly int erfere with the detection of tetracyclines.