Potential of simple, rapid, and non-target planar bioassay screening of veterinary drug residues

Veterinary drug residues in food samples of animal origin are currently analyzed by target analysis using high-performance liquid chromatography combined with sophisticated mass spectrometers. Since the results are only partially consistent with the microbiological results and positive findings occur rarely (in the per mil range in Germany), the potential of a simple planar bioassay screening was studied in the field of veterinary drug residue analysis. Using only a simple dilution of the milk for sample preparation, it was challenging to meet the maximum residue limits for antibiotic drug residues, exemplarily shown for the screening of two fluoroquinolones. However, the potential was evident for a simple, rapid, eco-friendly, and non-target screening without expensive instrumentation. Regardless of whether it is an active metabolite, contaminant, degradation product, or veterinary drug residue, the effect indicated on the planar surface due to bioassay detection will most likely also affect the human microbiome when consumed. The non-target screening of the milk samples revealed compounds with substantial antibacterial effects, which were not in the previous focus of interest. These antibacterial compounds will most likely also affect the human microbiome. Is it only the regulated antibiotic residues or generally all antibiotic compounds in a sample that count for consumer protection? The current prevailing understanding of food safety and antimicrobial resistance, based on the results of target (rather than effect) analyses, is being challenged. Non-target planar bioassay screening has been shown to fill a current gap by providing an understanding of inconsistencies and complementing routine target analysis of veterinary drug residues. As a highlight, it provides the full picture of the real levels of active compounds, regardless of the permitted limits of antibiotics.