AUTHOR=Cheng Ping , Yang Yuqi , Cao Sai , Liu Haibin , Li Xiaoting , Sun Jichao , Li Fulei , Ishfaq Muhammad , Zhang Xiuying 

TITLE=Prevalence and Characteristic of Swine-Origin mcr-1-Positive Escherichia coli in Northeastern China

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.712707

DOI=10.3389/fmicb.2021.712707

ISSN=1664-302X

ABSTRACT=<p>The emergence of the plasmid-mediated colistin resistance gene <italic>mcr-1</italic> is threatening the last-line role of colistin in human medicine. With <italic>mcr-1</italic>-positive <italic>Escherichia coli</italic> (<italic>E. coli</italic>) isolated from food animal being frequently reported in China, the prevalence of <italic>mcr-1</italic> in food animal has attracted public attention. In the present study, a total of 105 colistin-resistant <italic>E. coli</italic> strains were isolated from 200 fecal samples collected from six swine farms in northeastern China. <italic>mcr</italic>-PCR revealed that the prevalence of <italic>mcr-1</italic> in colistin-resistant <italic>E. coli</italic> was 53.33% (56/105). <italic>mcr-1</italic>-positive <italic>E. coli</italic> showed extensive antimicrobial resistance profiles with the presence of additional resistance genes, increased expression of multidrug efflux pump-associated genes, and increased biofilm formation ability. MLST differentiated all the <italic>mcr-1-</italic>positive <italic>E. coli</italic> into 25 sequence types (STs) and five unknown ST, and the most common ST was ST10 (<italic>n</italic> = 11). By phylogenetic group classification, the distribution of all <italic>mcr-1</italic>-positive <italic>E. coli</italic> belonging to groups A, B1, B2, and D was 46.43, 35.71, 5.36, and 5.36%, respectively. Conjugation experiment demonstrated that most of the <italic>mcr-1</italic> were transferable at frequencies of 2.68 × 10<sup>–6</sup>–3.73 × 10<sup>–3</sup> among 30 representative <italic>mcr</italic>-<italic>1-</italic>positive <italic>E. coli</italic>. The plasmid replicon types IncI2 (<italic>n</italic> = 9), IncX4 (<italic>n</italic> = 5), IncHI2 (<italic>n</italic> = 3), IncN (<italic>n</italic> = 3), and IncP (<italic>n</italic> = 1) were detected in the transconjugants. The results of growth assay, competition experiment, and plasmid stability testing showed that acquisition of <italic>mcr-1-</italic>harboring plasmids could reduce the fitness of bacterial hosts, but <italic>mcr-1</italic> remained stable in the recipient strain. Due to the potential possibility of these <italic>mcr-1</italic>-positive <italic>E. coli</italic> being transmitted to humans through the food chain or through horizontal transmission, therefore, it is necessary to continuously monitor the prevalence and dissemination of <italic>mcr-1</italic> in food animal, particularly in swine.</p>