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Co-Occurrence of Plasmid-Mediated Colistin Resistance (mcr-1) and Extended-Spectrum β-Lactamase Encoding Genes in Escherichia coli from Bovine Mastitic Milk in China.
Microbial Drug Resistance ( IF 2.3 ) Pub Date : 2020-06-08 , DOI: 10.1089/mdr.2019.0333
Gang Liu 1 , Tariq Ali 1, 2 , Jian Gao 1 , Sadeeq Ur Rahman 3 , Dan Yu 1 , Herman W Barkema 4 , Wenlin Huo 1 , Siyu Xu 1 , Yuxiang Shi 1, 5 , John P Kastelic 4 , Bo Han 1
Affiliation  

Both mcr-1 phosphoethanolamine transferase enzymes and extended-spectrum β-lactamases (ESBLs) are the main plasmid-mediated mechanisms of resistance to colistin and third-generation cephalosporins, respectively, and currently considered a major concern to humans and food animals. Prevalence of mcr-1 gene in Escherichia coli from dairy cattle has rarely been reported. Our objective was to determine prevalence and characteristics of mcr-1 carrying E. coli isolated from clinical mastitis cases in large dairy farms (>500 cows) in 16 provinces of China. A total of 249 E. coli was isolated from 2,038 mastitic milk samples. Among these isolates, 2.0% (n = 5) and 19.7% (n = 49) were colistin resistant mcr-1-positive and ESBL-producing isolates, respectively. All mcr-1-positive isolates that produced ESBLs also carried the blaCTX-M-15 gene and belonged to phylogroup-A. Most mcr-1 and blaCTX-M-15 genes were located on conjugative plasmids (IncP and IncF, respectively) that were successfully transferred to transconjugants in conjugation experiments. All mcr-1-positive E. coli isolates were multidrug resistant, exhibiting resistance to common antimicrobials. Multilocus sequence typing of these mcr-1-carrying E. coli isolates revealed four sequence types, reflecting substantial diversity. Multilocus sequence analysis detected evolutionary connection of mcr-1 carrying isolates with our recently reported ESBL-producing E. coli isolates, raising concerns regarding fast dissemination between bacteria. To our knowledge, this was the first nation-wide report describing isolates of E. coli from mastitic milk samples collected on large dairy farms in China, carrying mcr-1 and blaCTX-M-15 genes on conjugative plasmids. We concluded that dairy cattle are a potential source of mcr-1-carrying and ESBL-producing E. coli.
更新日期:2020-06-08
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