Detection of tetracyclines with luminescent bacterial strains.

The performance of two bioluminescent Escherichia coli K-12 strains for the specific detection of the tetracycline family of antimicrobial agents was compared, and the analytical applicability of one of the strains was preliminarily evaluated. One sensor plasmid contained the bacterial luciferase operon of Photorhabdus luminescens under the control of the tetracycline-responsive element from transposon Tn10 (15). An analogous plasmid construction with firefly (Photinus pyralis) luciferase reporter gene was constructed, and these two divergent tetracycline-inducible light-emitting systems were compared for their suitability for the qualitative detection of tetracyclines. Both sensor strains behaved in a similar manner kinetically, and the most sensitive tetracycline response for both sensor strains was achieved in 90-120 min by performing the assay at 37 degrees C. The sensor strain containing the bacterial luciferase operon responded slightly more sensitively to different tetracyclines than the strain containing firefly luciferase gene. The sensor bacteria retained their inducibility in lyophilization, and freeze-dried cells detected tetracyclines as sensitively as freshly cultivated sensor cells. The preliminary results from the analysis of tetracycline-spiked pork serum samples indicated that these sensor bacteria could be used to screen veterinary samples for tetracycline residues in real-time.