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The aim of this study is to develop a new micellar electrokinetic capillary chromatography with field amplified sample stacking for the determination of five kinds of macrolide antibiotic residues in milk. The main factors that affect the separation and enrichment of these analytes were optimized. The optimum running buffer was composed of 60 mM phosphate, 5 mM sodium cholate, and 1.0 mM cetyltrimethyl ammonium bromide at pH 7.0. The separation voltage was 20 kV and the sample was electrokinetically injected at 10 kV for 120 s. The detection wavelength was set at 195 nm. Under the optimized conditions, the enrichment factor of tilmicosin, erythromycin, clarithromycin, roxithromycin, and tylosin were 866, 565, 908, 702, and 675, respectively. The limits of detection ranged from 0.002 to 0.004 mg/kg. The method shall meet the requirement of their maximum residue limits ruled by China, the European Union, the United States, and other countries. Practical applications The developed method has been applied successfully to the determination of the milk samples spiked at 0.05 and 0.1 mg/kg. The recoveries ranging from 72.8 to 93.7% demonstrate that the method can be applied to the detection of tilmicosin, erythromycin, clarithromycin, roxithromycin, and tylosin residues in milk.

Background The overuse of antibiotics in livestock is contributing to the burden of antimicrobial resistance in humans, representing a One Health challenge. Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has recently become a growing concern, and ST9 is the major LA-MRSA lineage in China and has emerged in clinical settings. Methods Antimicrobial susceptibility testing was used to evaluate the tetracycline resistance of ST9 MRSA collections, and gene cloning experiments were performed to explore the resistance mechanisms. Whole-genome sequencing and comparative genomics were used to analyse the genetic features of clinical ST9 isolates. A phylogenetic tree was constructed to investigate the relationship of human- and livestock-derived ST9 isolates. Results Clinical ST9 isolates were found to possess several types of resistance genes and resistance-related mutations and were multidrug-resistant. Notably, all clinical ST9 isolates were resistant to third-generation tetracyclines. Cloning experiments showed that both the acquisition of the tetracycline resistance gene tet(L)/tet(63) and a mutation in the rpsJ gene contributed to third-generation tetracycline resistance. Phylogenetic analysis showed that the ST9 isolates collected in healthcare systems were probably transmitted from livestock. The ST9 lineage underwent multiple interspecies recombination events and gained many resistance elements. Furthermore, the resistance to third-generation tetracyclines may have evolved under tetracycline pressure in livestock. Conclusions The evolution of ST9 MRSA in livestock and transmission of this clone between humans and livestock highlight the importance of establishing control strategies with the One Health approach to reduce the burden of antibiotic resistance.

The aim of the experiment is to establish a method for the determination of acrylamide in food by automatic accelerated solvent extraction-gas chromatography-mass spectrometry. D3-acrylamide was used as isotope internal standard, crushed samples were extracted and purified by automatic accelerated solvent, acrylamide was derivatized into 2,3-dibromopropanamide by potassium bromide and potassium bromate under acidic conditions, and then the derivative was extracted by ethyl acetate and detected by gas chromatography-mass spectrometry. The method had a good linear relationship in the concentration range of 10–2000 ng/mL, and the coefficient of determination (R2) was 0.9997. The detection limit of the method was 3 μg/kg. The quantification limit of the method was 10 μg/kg. The standard addition recovery of acrylamide was between 105 and 120%, and the relative standard deviation of the recovery of acrylamide was less than 3.0%. The experimental result showed that the method was simple, sensitive, efficient and accurate, and could be used for the determination of acrylamide in food.