Use of a Disc-Assay System to Detect Oxytetracycline Residues in Honey

A simple inexpensive disc-assay system for detection of oxytetracycline (OTC) in honey was developed. This bioassay involved diluting honey 1:1 (wt/wt) with 0.1 M phosphate buffer, pH 7.0, and applying 90 μl of this solution to a 0.5-in (12.7-mm) filter paper disc placed on Bacillus cereus -inoculated media. This test detected about 0.2 μg OTC/ml (0.4 μg OTC/g honey) without interference from natural antibacterial inhibitors in honey. It was also shown that a variety of materials contributed to the natural inhibitor effect in honey, including materials other than glucose oxidase-derived hydrogen peroxide and the osmotic effects of sugar.