This Method Helps to Identify Antibiotics in Vegetables

The method was validated by analyzing 17 sulfonamides, 16 quinolones, 6 macrolides, 5 beta-lactams, and 5 tetracyclines, with 7 isotope-labelled internal standards for all the antibiotic classes tested. The QuEChERS-based LC-MS/MS method was confirmed to be highly accurate and precise with recoveries of 70–100 percent and reproducibility of less than 20 percent for relative standard deviation (RSD) for most of the sulfonamide, macrolide, beta-lactam, and tetracycline antibiotics. Although they are still considered acceptable at higher than the SANTE/11813/2017 guideline standard of 30 percent, the recoveries of the quinolones were lower than those of the other antibiotic classes in different vegetables. However, this was not unexpected as similar findings have been reported with both SPE and QuEChERS methods (Food Analytical Methods 2018;11:2857–2864). The reproducibility and thus, precision was especially good for the analyses of the macrolide and beta-lactam antibiotic residues, with RSDs that were lower than the other antibiotic classes, particularly at low concentrations of 5 μg/kg. The limit of quantification (LOQ) was 2 μg/kg for most (~74 percent) of the antibiotics tested, and 5 μg/kg for the remaining (~26 percent) residues. The method is accurate for a wide range of concentrations, with the linearity range being 1–200 μg/L. The coefficient of determination (r2) was the requisite value higher than 0.995 for each residue; which guarantees the accurate quantification of each of the 49 antibiotics through the application of this method (Food Analytical Methods. 2018;11:2857–2864).

To confirm the accuracy of the qualitative results, the MS/MS spectra of the putative antibiotic residues in the positive samples were compared with the spectra of known target analytes housed in a reference library. This helped disqualify type I errors and confirm true positives. This final step, was facilitated by the simultaneous acquisition of the MRM scan data alongside the full scan MS/MS spectra in enhanced product ion (EPI) mode using information-dependent acquisition (IDA), which was uniquely possible with the use of the SCIEX QTRAP instruments. This final confirmatory step helps validate the utility and reliability of this method (Food Analytical Methods. 2018;11:2857–2864).

Fulfilling a Need

According to research, antibiotic resistance may cause 10 million deaths annually by 2050 (PLOS Medicine. 2016;13(11):e1002184). The startling figures show that greater efforts need to be made to eliminate the injudicious application of antibiotics. Moreover, further research and understanding of the presence of antibiotics in the environment is required since antibiotics can leach from the soil into aquifers or groundwater due to run-off. All organisms—human, animal, or vegetable—are therefore susceptible to being exposed unnecessarily and unknowingly to antibiotics. As such, they can unwittingly contribute to the development of antibiotic-resistant bacteria and other microbes (Scientific American. January 2006).

Not only is there a need for better standards and regulation, there is also a need for tools such as the method described here to allow scientists, regulators, farmers, retailers and even consumers to identify antibiotics in their food. A united effort needs to be made to protect our environment as well as human and animal health, while maintaining food safety. This could include the exploration of other ways to combat bacterial infection, using innovative new technologies such as clustered regularly interspaced short palindromic repeats (CRISPR) and the development of precision medicines (Nat Med. 2019;25:730–733). The development of our methodology, using QuEChERS and LC-MS/MS, is just one tool in the arsenal in the fight against antibiotic resistance.

Professor Liu is executive deputy director of the Agro-environmental Quality Supervision and Testing Center at the Agro-Environmental Protection Institute (AEPI), Ministry of Agriculture and Rural Affairs, in China.