Exploring the persistence and spreading of antibiotic resistance from manure to biocompost, soils and vegetables.

The main avenue in which antibiotic resistance enters soils is through the application of livestock manure. However, whether antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) persist and spread to vegetables with the application of manure and manure products is still unclear. This study assessed seven kinds of cultured ARB, 221 ARGs subtypes and three transposon genes in the vegetable production chain (from manure to biocompost, soils and vegetables). Results showed that at least 80% of ARB, ARGs and transposon genes were removed after aerobic composting. However, aerobic composting did not reduce the diversity of ARGs in pig and chicken manure. A total of 19 ARGs subtypes still persisted during aerobic composting. Compared to the temperature-thermophilic stage, the number of bacteria resistant to erythromycin, the relative abundance of ARGs and IS613 increased 1.7-4.9 times at the temperature-decreasing stage. Direct application of biocompost introduced 11 ARGs subtypes to pakchoi, but these ARGs did not present in biocompost-amended soil. A transposon gene tnpA was also detected in the biocompost-amended soil, but surprisingly was found in the control vegetable. This demonstrated that the transposon gene is intrinsic in pakchoi. Bacterial community analysis and network analysis revealed that a specific genus Terrisporobacter carrying tetO, tetW ermB and tnpA persisted in the vegetable production chain, which may generate a potential risk in the following production. Our study illuminates the persistence and spreading of antibiotic resistance in the vegetable production chain which could help manage the ecological risks arising from antibiotic resistance in manure sources.