Epidemiologic and genomic insights on mcr-1-harbouring Salmonella from diarrhoeal outpatients in Shanghai, China, 2006–2016Research in context

Background: Colistin resistance mediated by mcr-1-harbouring plasmids is an emerging threat in Enterobacteriaceae, like Salmonella. Based on its major contribution to the diarrhoea burden, the epidemic state and threat of mcr-1-harbouring Salmonella in community-acquired infections should be estimated. Methods: This retrospective study analysed the mcr-1 gene incidence in Salmonella strains collected from a surveillance on diarrhoeal outpatients in Shanghai Municipality, China, 2006–2016. Molecular characteristics of the mcr-1-positive strains and their plasmids were determined by genome sequencing. The transfer abilities of these plasmids were measured with various conjugation strains, species, and serotypes. Findings: Among the 12,053 Salmonella isolates, 37 mcr-1-harbouring strains, in which 35 were serovar Typhimurium, were detected first in 2012 and with increasing frequency after 2015. Most patients infected with mcr-1-harbouring strains were aged