Molecular Evidence for Intra- and Inter-Farm Spread of Porcine mcr-1-Carrying Escherichia coli in Taiwan.

Shun-Chung Hsueh,Ming-Tang Chiou,Po-Ren Hsueh,Yu-Tsung Huang,Chih-Cheng Lai,Chao-Nan Lin,Chun-Hsing Liao

doi:10.3389/fmicb.2020.01967

Abstract

From January 2013 to December 2018, 90 Escherichia coli isolates were collected from 90 sick pigs on 58 farms in seven cities in Taiwan. The minimum inhibitory concentrations (MICs) of the isolates to 14 antimicrobial agents were determined on the VITEK 2 system (bioMérieux, Marcy-l’Etoile, France), and the resistance to colistin was assessed via the reference broth microdilution (BMD) method. The mobilized colistin resistance genes (mcr) were determined for the colistin-resistant isolates, which displayed BMD MICs ≥ 4 mg/L. Genotypes of the mcr-positive E. coli isolates were determined by multilocus sequence typing, arbitrarily primed polymerase chain reaction (PCR), and pulsed-field gel electrophoresis. All of the isolates were tested for susceptibility to carbapenems. Fifty isolates (55.6%) were resistant to colistin, 39 of which (78%) were positive for the mcr-1 gene. E. coli isolates harboring mcr-1 were most frequent in 2017 (15/18, 83.3%), followed by 2018 (13/23, 56.5%), 2015 (7/21, 33.3%), and 2016 (3/24, 12.5%). A total of 18 sequence types (STs) were identified among the 39 porcine mcr-1-carrying E. coli isolates; 13 were ST2521 (33.3%) isolated in 2017 and 2018. Five genotypes (clones) were identified, and the same genotypes were in sick pigs on the same farm and different farms. This suggests intra- and inter-farm spread of porcine mcr-1-carrying E. coli. The results presented here indicate high colistin resistance and wide mcr-1 E. coli prevalence among the sick pigs sampled in 2015–2018 in different regions of Taiwan.

Highlights

The plasmid-borne mobilized colistin resistance-1 gene confers resistance to polymyxin E in Escherichia coli (Liu et al, 2016) and has been reported on nearly every continent (Nordmann et al, 2016; Meinersmann et al, 2017; Lai et al, 2018; Rebelo et al, 2018)
The prevalence of the mcr-1 gene in porcine E. coli isolates from different geographical regions of Taiwan may be unrelated to a specific clonal population
Our results suggest that further investigation is required to assess the clinical significance of ST2521 among mcr-1 positive E. coli isolates

Summary

Introduction

The plasmid-borne mobilized colistin resistance-1 gene (mcr-1) confers resistance to polymyxin E (colistin) in Escherichia coli (Liu et al, 2016) and has been reported on nearly every continent (Nordmann et al, 2016; Meinersmann et al, 2017; Lai et al, 2018; Rebelo et al, 2018). Enterobacteriaceae isolates positive for mcr-1 have been recovered from humans and animals, mcr-1-Positive E. coli in Pigs including chickens, turkeys, swine, and pets (Brennan et al, 2016; Kempf et al, 2016; Kuo et al, 2016; Khan et al, 2017; Pulss et al, 2017; Lai et al, 2018). The use of colistin in animal husbandry in Taiwan has been restricted since July 2007, but mcr-1-harboring E. coli isolates are still a concern. The prevalence of mcr-1 in meat-associated E. coli isolates has increased in Taiwan, with rates of 1.1, 6.6, and 8.7% in 2012, 2013, and 2015, respectively (Kuo et al, 2016)

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Results

Conclusion