Development and validation of a potentiometric biosensor assay for tylosin with demonstrated applicability for the detection of two other antimicrobial growth-promoter compounds in feedstuffs.

A potentiometric biosensor assay based on a commercially available polyclonal antibody was developed to detect tylosin residues in animal feed. The method can be used as a rapid (less than 45 min) laboratory-based procedure or as a portable field-test for the simultaneous measurement of up to 12 different samples. For both procedures the qualitative detection capability (CCß) for tylosin was determined as 0.2 mg kg(-1) in a range of animal feeds with a measurement repeatability at concentrations between 0.2 and 4 mg kg(-1) of ≤13% coefficient of variation (%CV). The field-test format was capable of detecting tylosin residues at operating (external air) temperatures ranging between +4 and 37°C, although some reduction in signal was observed at the lower temperatures. The laboratory-based tylosin assay was evaluated using 16 medicated and 22 non-medicated feeds and was found to give comparable data with a confirmatory method based upon liquid chromatography-tandem mass spectrometry (LC-MS/MS). The potential to develop a multi-probe format assay for the simultaneous detection of tylosin, spiramycin and virginiamycin was also demonstrated. Cross-validation in a second laboratory showed the assay to be transferable, reliable and robust.

New method for the rapid identification of tetracycline residues in foods of animal origin - using the PremiTest in combination with a metal ion chelation assay.

A post-screening classification assay for tetracycline compounds has been developed and integrated into the previously reported optimized PremiTest methodology. The new post-antimicrobial screening assay is based on a metal ion chelation using calcium and sodium chloride and has been shown to be specific towards the tetracycline class. The assay is both cost-effective and complementary to the post-screening procedures that have previously been developed for the beta-lactam and sulfonamide compounds. A validation study was conducted in accordance with 2002/657/EC (Commission Decision). The method is rugged and applicable to a range of tetracyclines of differing antimicrobial potencies over a wide concentration range. A blind trial was undertaken in which all antimicrobial residues in the unknown samples were successfully identified by the analyst following the integrated PremiTest procedure for the classification of antimicrobial compounds.