ISEc69-Mediated Mobilization of the Colistin Resistance Gene mcr-2 in Escherichia coli

Objectives: The emergence of mobile colistin resistance genes has compromised the efficacy of the last resort antibiotic, colistin, in clinical treatment. The mcr-2 gene was first identified in Belgium in association with the insertion sequence ISEc69. However, the molecular mechanisms of mcr-2 mobilization are not well understood. Methods: To further explore the mobilization of mcr-2 gene via ISEc69, we constructed a conjugative plasmid that carries an intact composite transposon Tn7052. Transposition assays were performed by conjugation, the transposition sites were characterized by arbitrary primed PCR and DNA sequencing. Results: In this study, we experimentally demonstrated that mcr-2 could be mobilized as a composite transposon Tn7052 and its transposition generated 8-bp AT-rich duplications in the host genome. Conclusion: These results indicate that mcr-2 gene could be mobilized by ISEc69, the current investigations provide mechanistic insights in the transposition of mcr-2.