Spread of Plasmids Carrying Antibiotic Resistance Genes in Soil-Lettuce-Snail Food Chain

Abstract

Agricultural activities such as fertilization change the composition of antibiotic resistance genes(ARGs) and their host bacteria in agricultural fields, while complex microbial activities contribute to the transfer of ARGs and their host bacteria into crops and their transmission to humans through the consumption of agricultural products. The spread of plasmid-mediated ARGs in the farm food chain is unknown, as is the risk of their transfer to human pathogenic bacteria. Therefore, this study constructed a farmland food chain with soil-lettuce-snail as a typical structure, added genetically engineered Pseudomonas fluorescens containing multidrug-resistant plasmid RP4 to track its spread in the farmland food chain, and used different fertilization methods (no fertilization, chemical fertilizer application and manure application) to explore its influence on the spread and diffusion of ARGs and intl1 in the farmland food chain. It was found that exogenous Pseudomonas can enter plants from soil and pass into snails' intestines, and there is horizontal gene transfer phenomenon of RP4 plasmid in bacteria. The addition of exogenous drug-resistant bacteria had different effects on the total abundance of ARGs and intl1 at different interfaces of the food chain, but fertilization, especially manure, not only promoted the spread of Pseudomonas aeruginosa and the transfer of RP4 plasmid levels, but also significantly increased the total abundance of ARGs and intl1 at all interfaces of the food chain. The main ARGs host bacteria in the food chain include Proteobacteria, Bacteroides and Firmicutes, while Flavobacterium of Bacteroides is the unique potential host bacteria of RP4 plasmid, and fertilization obviously increases the abundance of Bacteroides. To sum up, this study provides reference for the risk assessment of ARGs spreading to human body through food chain.