Abstract

The emergence and transmission of the mobile colistin resistance gene (mcr-1) threatened the extensive use of polymyxin antimicrobials. Accumulated evidence showed that the banning of colistin additive in livestock feed efficiently reduce mcr-1 prevalence, not only in animals but also in humans and environments. However, our previous study has revealed that a small proportion of Escherichia coli could continually carry chromosomally-encoded mcr-1. The chromosomally-encoded events, indicated the existence of stabilized heritage of mcr-1 and revealed a potential threat in the antimicrobial stewardship interventions, are yet to be investigated. In this study, we systematically investigated the genetic basis of chromosomally-encoded mcr-1 in prevalence and potential mechanisms of lineage, plasmid, insertion sequence, and phage. Our results demonstrated that the emergence of chromosomally-encoded mcr-1 could originate from multiple mechanisms, but mainly derived through the recombination of ISApl1/Tn6330. We reported a specific transmission mechanism, which is a phage-like region without lysogenic components, could associate with the emergence and stabilization of chromosomally-encoded mcr-1. These results highlighted the potential origin and risks of chromosomally-encoded mcr-1, which could be a heritable repository and thrive again when confronted with new selective pressures. To the best of our knowledge, this is the first study to systematically reveal the genomic basis of chromosomally-encoded mcr-1, and report a specific transmission pattern involved in phage-like region. Overall, we demonstrate the origin mechanisms and risks of chromosomally-encoded mcr-1. It highlights the need of public attention on chromosome-encoded mcr-1 to prevent from its reemergence.

Highlights

  • The emergence and transmission of the mobile colistin resistance gene threatened the extensive use of polymyxin antimicrobials

  • Our previous study showed that a low proportion of Escherichia coli carrying chromosomally-encoded mcr-1 continually existed in the ecosystem [4], which was sporadically reported by other studies as well [9,10,11]

  • On account of the plasmid that could be lost under certain circumstances due to instability, the chromosomally-encoded events could stabilize the heritage of mcr-1, threatening the intervention of colistin stewardship

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Summary

Introduction

The emergence and transmission of the mobile colistin resistance gene (mcr-1) threatened the extensive use of polymyxin antimicrobials. We systematically investigate the epidemiological and genomic characterizations of E. coli population with chromosomally-encoded mcr-1. Based on our previous large-scale epidemiological study from 2016 to 2018 in Guangzhou, China [4], we identified 24 (3.5%) out of 688 mcr-1-positive E. coli isolates with the chromosomally-encoded mcr-1 (Table 1).

Results
Conclusion
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