Co-selection may explain the unexpectedly high prevalence of plasmid-mediated colistin resistance gene <i>mcr-1</i> in a Chinese broiler farm
Yuping Cao, 华南农业大学兽医学院，广东 广州510642，中国, Qingqing Lin, Wan-Yun He, Jing Wang, Meng-Ying Yi, Luchao Lv, Jun Yang, Jian–Hua Liu, Jianying Guo, 岭南现代农业科学与技术广东省实验室，广东 广州510642，中国
Abstract
The rise of the plasmid-encoded colistin resistance gene <i>mcr-1</i> is a major concern globally. Here, during a routine surveillance, an unexpectedly high prevalence of <i>Escherichia coli</i> with reduced susceptibility to colistin (69.9%) was observed in a Chinese broiler farm. Fifty-three (63.9%)<i> E. coli</i> isolates were positive for <i>mcr-1</i>. All identified <i>mcr-1</i>-positive <i>E. coli</i> (MCREC) were multidrug resistant and carried other clinically significant resistance genes. Furthermore, the <i>mcr-1</i> genes were mainly located on the IncI2 and IncHI2 plasmids. Conjugation experiments unraveled the co-transfer of <i>mcr-1</i> with other antibiotic resistance genes (<i>bla</i><sub>CTX-M-55</sub>, <i>bla</i><sub>CTX-M-14</sub>, <i>floR</i>, and <i>fosA3</i>) via the IncI2 (<i>n</i>=3) and IncHI2 (<i>n</i>=4) plasmids. The stable genetic context <i>mcr-1</i>-<i>pap2</i> was common in the IncI2 plasmids, whereas IS<i>Apl1</i>-<i>mcr-1</i>-<i>pap2</i>-IS<i>Apl1</i> was mainly found in the IncHI2 plasmids. The dominance of <i>mcr-1</i>-bearing IncI2 and IncHI2 plasmids and co-selection of <i>mcr-1 </i>with other antimicrobial resistance genes might contribute to the exceptionally high prevalence of <i>mcr-1</i> in this broiler farm. Our results emphasized the importance of appropriate antibiotic use in animal production.