Effects of colistin stress on growth, antioxidant system and metabolite pattern of lettuce

The widespread of colistin resistance gens has aroused great public concern, and many efforts have been made to re-evaluate the application of colistin in veterinary medicines. Most of colistin is excreted with feces, while no literature has reported the determination of colistin in plants and its accumulation on the potential toxicity to plant life. In this study, a rapid and eco-friendly method using liquid chromatography tandem mass spectrometry (LC-MS/MS) based on dispersive solid-phase extraction was developed for detecting colistin in lettuce and was successfully applied to real samples. Furthermore, the toxic effects of colistin exposure on the growth, oxidative stress, and metabolism of lettuce were investigated.

The LC-MS/MS results showed that the developed method had good linear correlation. Average recoveries of colistin at four spiked concentrations (10, 30, 100, and 300 µg/kg) ranged from 73.3% to 91.1%, and the limit of detection (LOD) was 5 µg/kg. Colistin may stimulate lettuce seed germination, although the difference was not significant; however, it can significantly inhibit lettuce growth in a dose-dependent manner. Colistin can damage mitochondria and chloroplasts, blocking photosynthetic efficiency and energy metabolism, thereby inhibiting lettuce growth. This harmful effect is probably associated with the suppression of the phospholipid-arachidonic acid metabolic pathway, during which colistin upregulated 11 (R)-HETE and reduced 5,6-DHET and prostaglandin G2. Consequently, malondialdehyde, peroxidase, and superoxide dismutase were significantly elevated, while catalase was diminished, triggering lipid peroxidation and the excessive accumulation of oxidative stress indicators. Finally, based on detection results from real samples collected at local supermarkets, the hazard quotient was below 1, indicating a low health risk of colistin in lettuce for local residents through dietary intake.

This study developed a rapid LC-MS/MS method for the detection of colistin in lettuce. Colistin was found to upregulate 11 (R)-HETE and decrease 5,6-DHET and prostaglandin G2 by inhibiting the phospholipid-arachidonic acid metabolic pathway, thereby inducing oxidative stress and compromising organelle integrity in lettuce. Analysis of real samples indicated that the potential health risk from colistin exposure through dietary intake is low. Nevertheless, further research is required to evaluate the potential risks related to antibiotic resistance and the synergistic toxicity of colistin in combination with other contaminants.