Portugal - MCR-1 gene (Colistin resistance) found in 2011 Salmonella Isolate

[Gert van der Hoek]

Dissemination of the mcr-1 colistin resistance gene

Published Online: 17 December 2015

We read with interest the Article by Yi-Yun Liu and colleagues1 reporting the high rates of plasmid-mediated colistin resistance in Escherichia coli isolates from animal food sources in China. We share their concerns about potential widespread dissemination of the mcr-1 gene, which could lead to substantial morbidity and mortality associated with colistin failure in the clinical setting.
The authors pointed out that identical genes were identified in E coli isolates sequenced by researchers in Malaysia, and thereby suggested that plasmid-mediated colistin resistance might already be present in southeast Asia. However, an identical gene is also present in a Salmonella enterica serotype Typhimurium isolate (GenBank accession number NZ_LFCC01000022) from a food sample in Portugal in 2011.2 As meat products might include meat from several sources or be contaminated during processing, this discovery does not necessarily imply the presence of mcr-1-harbouring organisms in European farms. Nonetheless, the European population might have been exposed to mcr-1-harbouring organisms.

We believe that the mcr-1 gene is more mobile than suggested by Liu and colleagues, and has spread beyond Asia into Europe. We echo the call by Liu and colleagues, which has been substantiated by Paterson and Harris,3 to curtail the agricultural use of colistin, and emphasise the importance for a comprehensive strategic framework against antimicrobial resistance in China.4 Additionally, specific strategies to mitigate the spread of antimicrobial resistance across geographical boundaries, such as judicious use of antibiotics in travellers,5 should be reinforced.