Characterization Of Chromosome-Mediated Colistin Resistance In Escherichia coli Isolates From Livestock In Korea

Abstract

Purpose

Colistin resistance in gram-negative bacteria from humans and livestock has been increasingly reported worldwide. The aim of this study was to investigate the underlying mechanisms of chromosome-mediated colistin resistance in Escherichia coli isolates from livestock in Korea.

Materials and methods

Thirty mcr-1-negative isolates were selected from a collection of colistin-resistant E. coli isolates collected from livestock in 2005 and 2015 in Korea. Amino acid alterations in PmrAB, PhoPQ, MgrB, and PmrD were investigated. Colistin-resistant derivatives were produced by serial passage of colistin-susceptible E. coli isolates in colistin-containing media.

Results

Thirty colistin-resistant mcr-negative E. coli isolates were classified into 26 sequence types. Twenty-two isolates carried diverse amino acid alterations in PmrB, PhoP, PhoQ, MgrB, and/or PmrD, whereas no mutation in any of these genes was found in the remaining eight isolates. Sixteen out of the 22 isolates shared a total of nine polymorphic positions that were found in colistin-susceptible E. coli strains. Colistin-resistant derivatives from two colistin-susceptible isolates showed the same genetic alterations that were observed in colistin-resistant clinical isolates.

Conclusion

Our results suggest that the mechanism underlying chromosome-mediated colistin resistance remain to be discovered in E. coli. Selective pressure of colistin in vitro induced the same genetic mutations associated with colistin resistance in vivo. Efforts to reduce colistin consumption in livestock should be redoubled, to prevent the occurrence of colistin-resistant E. coli strains.

Keywords:

• colistin resistance
• two-component system
• livestock
• genetic mutation
• mcr gene

Acknowledgments

This study was supported by a grant from the Animal and Plant Quarantine Agency, Ministry of Agriculture, Food, and Rural Affairs, Republic of Korea (Z-1543081-2017-18-01). The abstract of this paper was presented at the 27th Federation Meeting of Korean Basic Medical Scientists 2019 as a poster presentation with interim findings.

Disclosure

The authors report no conflicts of interest in this work.