Distribution of antibiotic resistance genes and their pathogen hosts in duck farm environments in south-east coastal China.

Livestock farms are major reservoirs of antibiotic resistance genes (ARGs) that are discharged into the environment. However, the abundance, diversity, and transmission of ARGs in duck farms and its impact on surrounding environments remain to be further explored. Therefore, the characteristics of ARGs and their bacterial hosts from duck farms and surrounding environment were investigated by using metagenomic sequencing. Eighteen ARG types which consist of 823 subtypes were identified and the majority conferred resistance to multidrug, tetracyclines, aminoglycosides, chloramphenicols, MLS, and sulfonamides. The floR gene was the most abundant subtype, followed by sul1, tetM, sul2, and tetL. ARG abundance in fecal sample was significantly higher than soil and water sample. Our results also lead to a hypothesis that Shandong province have been the most contaminated by ARGs from duck farm compared with other four provinces. PcoA results showed that the composition of ARG subtypes in water and soil samples was similar, but there were significant differences between water and feces samples. However, the composition of ARG subtypes were similar between samples from five provinces. Bacterial hosts of ARG subtypes were taxonomically assigned to eight phyla that were dominated by the Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. In addition, some human bacterial pathogens could be enriched in duck feces, including Enterococcus faecium, Acinetobacter baumannii, and Staphylococcus aureus, and even serve as the carrier of ARGs. The combined results indicate that a comprehensive overview of the diversity and abundance of ARGs, and strong association between ARGs and bacterial community shift proposed, and benefit effective measures to improve safety of antibiotics use in livestock and poultry farming. KEY POINTS: • ARG distribution was widespread in the duck farms and surroundings environment • ARG abundance on the duck farms was significantly higher than in soil and water • Human bacterial pathogens may serve as the vectors for ARGs.