Improved microbial screening assay for the detection of quinolone residues in poultry and eggs.

An improved microbiological screening assay is reported for the detection of quinolone residues in poultry muscle and eggs. The method was validated using fortified tissue samples and is the first microbial assay to effectively detect enrofloxacin, difloxacin, danofloxacin, as well as flumequine and oxolinic acid, at or below their EU maximum residue limits (MRL). The accuracy of the assay was shown by analysing incurred tissue samples containing residue levels around the MRL. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantification of the quinolone concentration in these samples showed that the test plate can be used semi-quantitatively, allowing the definition of an "action level" as an inhibition zone above which a sample can be considered "suspect". The presented assay is a useful improvement or addition to existing screening systems.