Researchers have now discovered a new mobile colistin resistance gene, mcr–3, in E. coli of pig origin. The novel mcr–3 gene was discovered when a colistin–resistant Escherichia coli isolate tested negative for both mcr–1 and mcr–2. This novel mobile colistin resistance gene may already be widely disseminated. Screening for the mcr–3 gene should be urgently included in the surveillance of colistin–resistant Gram–negative pathogens from animals, humans, and the environment.

The E. coli mcr–3 sequence is similar to sequences found in Enterobacteriaceae and Aeromonas, which are commonly found in the environment. Due to the potential transfer of mcr–3 between these bacterial species, the prevalence of mcr–3 may be largely underestimated. Because colistin is widely used in veterinary medicine, and is being used with increasing frequency in human medicine, it is essential to continually monitor the mobile colistin resistance determinants in order to tackle the dissemination of mcr genes in the agricultural and healthcare sectors.

The study was published in the journal mBio on June 27, 2017.