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DEAR EDITOR,rnThe rise of the plasmid-encoded colistin resistance gene mcr1 is a major concern globally.Here, during a routine surveillance, an unexpectedly high prevalence of Escherichia coil with reduced susceptibility to colistin (69.9％) was observed in a Chinese broiler farm.Fifty-three (63.9％) E.coli isolates were positive for mcr-1.All identified mcr-1-positive E.coli (MCREC) were multidrug resistant and carried other clinically significant resistance genes.Furthermore, the mcr-1 genes were mainly located on the Incl2 and IncHl2 plasmids.Conjugation experiments unraveled the co-transfer of mcr-1 with other antibiotic resistance genes (blacTX-M-55, b/acTX-M-14, floR, and fosA3) via the Incl2 (n=3) and IncHl2 (n=4) plasmids.The stable genetic context mcr-1-pap2 was common in the Incl2 plasmids, whereas ISApl1-mcr-1-pap2-ISApl1 was mainly found in the IncHl2 plasmids.The dominance of mcr-1-bearing Incl2 and IncHl2 plasmids and co-selection of mcr-1 with other antimicrobial resistance genes might contribute to the exceptionally high prevalence of mcr-1 in this broiler farm.Our results emphasized the importance of appropriate antibiotic use in animal production.