Prevalence and molecular characteristics of mcr-1-positive Escherichia coli isolated from duck farms and the surrounding environments in coastal China

The emergence of colistin-resistance is considered a threat to public health and colistin-resistant bacteria have recently been reported in animal, environmental and human sources. Whereas, the epidemic and dissemination of colistin-resistant bacteria in duck farms have not been surveyed, especially the surrounding environmental contamination from duck farms. We investigated the prevalence and molecular characteristics of mcr-1-positive E. coli from duck farms in coastal China. 360 mcr-1-positive E. coli isolates were collected from 1112 samples from duck farms and surrounding environments. The prevalence of mcr-1-positive E. coli in Guangdong province was higher than other two provinces we examined. PFGE analysis indicated clonal spread of mcr-1-positive E. coli between duck farms and surrounding environments, including water and soil. MLST analysis demonstrated that ST10 was more common than ST1011, ST117, and ST48. Phylogenomic analysis also suggested mcr-1-positive E. coli collected from distinct cities were assigned to the same lineage and mcr-1 was primarily located on IncI2 and IncHI2 plasmids. Genomic environment analysis showed mobile gene elements ISApl1 most likely plays a key role in the horizontal transmission of mcr-1. WGS further revealed that mcr-1 was found associated with 27 different ARGs. Our findings emphasize the urgent need for effective colistin resistance surveillance in humans, animals and the environment.