Co-Occurrence of the mcr-1.1 and mcr-3.7 Genes in a Multidrug-Resistant Escherichia coli Isolate from China

Chongtao Du,^1,* Yuyang Feng,^1,* Guizhen Wang,² Zhiyuan Zhang,¹ Huimin Hu,¹ Yu Yu,¹ Jiayang Liu,¹ Lihao Qiu,¹ Hongtao Liu,¹ Zhimin Guo,³ Jing Huang,³ Jiazhang Qiu<sup>1

1</sup>Key Laboratory of Zoonosis, Ministry of Education, College of Veterinary Medicine, Jilin University, Changchun 130062, People’s Republic of China; ²College of Food Engineering, Jilin Engineering Normal University, Changchun 130052, People’s Republic of China; ³Department of Clinical Laboratory, The First Hospital of Jilin University, Changchun 130021, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Jiazhang Qiu
College of Veterinary Medicine, Jilin University, No. 5333 Xi’an Road, Changchun 130062, People’s Republic of China
Email qiujz@jlu.edu.cn
Jing Huang
Department of Clinical Laboratory, The First Hospital of Jilin University, Changchun 130021, People’s Republic of China
Email huangj@jlu.edu.cn

Objective: A colistin-resistant Escherichia coli strain isolated from dog feces was characterized in this study.
Methods and Results: A multiplex PCR assay was used to detect the presence of colistin-resistant mcr genes; it was found that E. coli QDFD216 co-harbored the mcr-1 and mcr-3 genes. Whole-genome sequencing and further bioinformatics analysis revealed that E. coli QDFD216 belonged to serotype O176:H11, fimH1311 type and ST132. The resistance genes bla_CTX-M-14, mdfA, dfrA3, acrA, acrB, tolc, and sul3 were present in the chromosome. The mcr-1.1 and mcr-3.7 genes were located in two plasmids of different incompatibility groups. mcr-1.1 was carried by a IncX4-type plasmid within an typical IS 26-parA-mcr-1.1-pap2 cassette, while mcr-3.7 was encoded by an IncP1-type plasmid with a genetic structure of TnAs2-mcr-3.7-dgkA-IS 26. No additional antibiotic resistance genes were carried by either plasmid.
Conclusion: This is the first report of an E. coli isolate co-harboring a mcr-1.1-carrying IncX4 plasmid and a mcr-3.7-carrying IncP1 plasmid. The evolution and mechanism of mcr gene co-existence need further study to assess its impact on public health.

Keywords: colistin resistance, whole-genome sequencing, mcr genes, mcr-1, mcr-3