Rapid fluorescence screening assay for tetracyclines in chicken muscle

A simple, rapid fluorescence assay was developed for screening tetracyclines in chicken muscle at the U.S. tolerance level (2 mg/kg). The method requires only a homogenization of the tissue in acetonitrile-ammonium hydroxide, centrifugation, addition of Mg+2, and another centrifugation before fluorescence of the supernatant is measured at 505 nm (excitation at 385 nm). Comparison of the fluorescence of control chicken muscle extracts with extracts from muscle fortified with either 2 mg/kg tetracycline, oxytetracycline, or chlortetracycline showed no overlap. A threshold level set at the average fluorescence for a series of fortified 2 mg/kg samples minus 3sigma minimized false-negative responses to provide a successful screening method. The method was tested with blinded samples as controls or samples fortified with tetracycline, oxytetracycline, or chlortetracycline in order to demonstrate its utility. This approach can provide an alternative to microbial screening assays.