MCR-1 in multidrug-resistant and copper-tolerant clinically relevant Salmonella 1,4,[5],12:i:- and S. Rissen clones in Portugal, 2011 to 2015

The mcr-1 gene was found in 11 isolates from a Portuguese Salmonella collection (n = 1,010; 58 serotypes; 2002-15) of clinical samples, foodstuff, food-animals and water. Mcr-1 has been located on different plasmids (IncX4/IncHI2) in pig-associated multidrug-resistant, copper-tolerant S.1,4,[5],12:i:-/ST34 and S. Rissen/ST469 clones from human and pork products since at least 2011. Our data highlight dissemination of mcr-1 by successful resistant clones in Europe and raise questions about the efficacy of copper-based interventions to reduce colistin use.