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Nitrofurazone usage in food‐producing animals is prohibited in most countries, including the United States. Regulatory agencies regularly monitor its use in domestic, export/import animals' food products by measuring the semicarbazide (SEM) metabolite as a biomarker of nitrofurazone exposure. However, the use of SEM is controversial because it is also produced in food naturally and thus gives false positive results. A cyano‐metabolite, 4‐cyano‐2‐oxobutyraldehyde semicarbazone (COBS), is proposed as an alternate specific marker of nitrofurazone to distinguish nitrofurazone from treated or untreated animals. A synthetic method was developed to produce COBS via metallic hydrogenation of nitrofurazone. The product was isolated and characterized by one‐ and two‐dimensional nuclear magnetic spectroscopy (NMR) experiments, Fourier‐transform infrared spectroscopy (FT‐IR), and mass spectrometry. The developed synthetic procedure was further extended to synthesize isotopically labeled 4‐[13C]‐cyano‐2‐oxo‐ [2, 3, 4‐13C3]‐butyraldehyde semicarbazone. Labeled COBS is useful as an internal standard for its quantification in food‐producing animals. Thus, the developed method provides a possibility for its commercial synthesis to procure COBS. This is the first synthesis of the alternate specific marker metabolite of nitrofurazone for possible usage in regulatory analysis to solve a real‐world problem. [ABSTRACT FROM AUTHOR]

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Enrofloxacin and danofloxacin are the only fluoroquinolone antibiotics approved for use in cattle in the United States. Microbial screening methods commonly used for monitoring veterinary drug residues are not sensitive or selective for fluoroquinolones. In this work, a luminescence-based screening assay was developed to detect fluoroquinolones in beef serum. This approach takes advantage of the DNA-enhanced luminescence signal of a fluoroquinolone–Tb+3complex. In this method, serum samples were extracted with acidified acetonitrile in the presence of magnesium sulfate. After centrifugation, evaporation of the supernatant was followed by dissolution of the residue in buffer and filtration. Addition of Tb+3and DNA then allowed a reading of the luminescence signal. The technique was illustrated using enrofloxacin, and provided good recoveries (73–88%) at 25, 50 and 100 ng ml−1, with reasonable RSDs averaging at 11%. The LOD was 2.5 ng ml−1based on the variability of response of control serum samples from 18 different steers. The method provided no false-positive or false-negative results while screening blind samples for enrofloxacin and was demonstrated to be quantitative over a range of 0–100 ng ml−1. [ABSTRACT FROM AUTHOR]

In 2019, the U.S. Department of Agriculture's (USDA) Food Safety and Inspection Service (FSIS) provided revised guidance for labeling claims of "raised without antibiotics" (RWA) and similar terms for meat and poultry produced in the US. In 2022, Price et al. published a study reporting that 15% of RWA-labeled cattle contained antibiotic residues in urine samples. In 2023, the USDA embarked on the project reported herein to independently determine the extent of antibiotic drug residues present in kidney and liver tissues from slaughtered cattle purported to be RWA. In this study, FSIS inspectors randomly collected kidney and liver tissues from 189 RWA animals in 79 slaughter establishments across the US. The samples were monitored for 185 veterinary drugs multiple times by different means, including liquid-chromatography coupled with tandem mass spectrometry (LC-MS/MS) and quadrupole high-resolution MS with an orbital ion trap instrument (LC-Q/orbitrap). Samples from 37 animals (20%) met the analytical identification criteria for at least one antibiotic confirmed in at least two analyses. Multiple antibiotics were determined in 11 RWA animals. Macrolides (tulathromycin, tildipirosin, tilmicosin, and gamithromycin) were confirmed in 20 (11%) of the RWA animals. The ionophore, monensin, was also confirmed in tissues from 11 samples, with unconfirmed/partial identifications in 8 others. Tetracyclines were confirmed in samples from 12 animals, several of which were found to contain multiple antibiotic residues. One animal each was also found to be positive for sulfamethazine (a sulfonamide antibiotic) and metabolites of penicillin G (a β-lactam antibiotic). Although they are not antibiotics, two anthelmintics (fenbendazole and eprinomectin) were confirmed in tissues from 3 RWA animals. FSIS has informed the slaughter establishments with positive results and advised them to conduct a root cause analysis and implement corrective actions.

A simple, rapid fluorescence assay was developed for screening tetracyclines in chicken muscle at the U.S. tolerance level (2 mg/kg). The method requires only a homogenization of the tissue in acetonitrile-ammonium hydroxide, centrifugation, addition of Mg+2, and another centrifugation before fluorescence of the supernatant is measured at 505 nm (excitation at 385 nm). Comparison of the fluorescence of control chicken muscle extracts with extracts from muscle fortified with either 2 mg/kg tetracycline, oxytetracycline, or chlortetracycline showed no overlap. A threshold level set at the average fluorescence for a series of fortified 2 mg/kg samples minus 3sigma minimized false-negative responses to provide a successful screening method. The method was tested with blinded samples as controls or samples fortified with tetracycline, oxytetracycline, or chlortetracycline in order to demonstrate its utility. This approach can provide an alternative to microbial screening assays.