MCR-1 Gene (Colistin Resistance) Has Spread in the Foodchain - Worldwide Distribution of MCR-1 Might Be Underestimated.

[Gert van der Hoek]

Published Online: 17 December 2015

Yi-Yun Liu and colleagues1 reported identification of the plasmid-mediated colistin resistance gene mcr-1 in China. They noted that mcr-1 positive Enterobacteriaceae were present in animal retail meat and in patients with infection during 2011?14. They suggested that mcr-1 is currently confined to China and might have spread to southeastern Asia.

We retrieved the mcr-1 gene sequence and traced this gene in available public bacterial gene datasets including metagenomes (figure). We were surprised to find that the complete mcr-1 gene was present (100% nucleotide identity) in three Chinese human gut microbiomes of 1267 human fecal samples from Europe, China, and the USA. Additionally, raw reads mapping identified mcr-1gene fragments in another 24 Chinese gut samples. These mcr-1-harbouring Chinese gut samples were presumably sampled before 2011, considering that the paper in which the samples are reported was submitted in August, 2011.3 These results suggest that the mcr-1 gene might have been in China for a long time and already spread to the healthy human gut, which is regarded as an antibiotic resistance gene reservoir4 and a site with high horizontal gene transfer potential.5

Because of limited genome data, especially the lack of genomes for colistin resistance isolates, we are concerned that the worldwide distribution of mcr-1 might be underestimated. Collectively, the widespread distribution of the mcr-1 gene in meat and food samples, and its presence in the human microbiome, strongly suggest a potential food chain dissemination pathway, which warrants immediate worldwide attention.