Strong antibacterial effects in animal-derived food detected via non-target planar bioassays

Abstract

Screening for antibiotic residues in animal-derived food is largely done by in vitro assays. However, a non-negligible number of positive screening results (sum values) remains with no confirmation by high-performance liquid chromatography coupled to high-sophisticated mass spectrometers. To investigate this inconsistency, a hyphenated strategy was sought that combines on the same surface planar chromatography−multi-imaging with antibacterial planar bioassays. Strong antibacterial activity against Gram-positive and Gram-negative bacteria was revealed in four animal-derived food extracts (pig muscle, cow milk, chicken eggs, and honey), which, however, were previously proven to be veterinary drug residue-free. This antibacterial effect was strong, extremely exceeding the effect from a mixture of 81 veterinary drugs spiked at 300 µg/kg, which is about 3 times the maximum residue limit of most of these veterinary drugs. The unknown antibacterial zones were online-eluted to high-resolution mass spectrometry to obtain molecular formulas. Endogenous fatty acids and lipids were identified to be responsible for the strong antibacterial effects, confirmed by co-analyzed reference compounds. These results resolved the methodological inconsistency but also question the prevailing understanding: Current food safety only based on target analysis of regulated antibiotic residues neglects consumer protection when the much stronger antibacterial impact of food on the human microbiome is overlooked.