Probably catalyzes the addition of a phosphoethanolamine moiety to lipid A. Phosphoethanolamine modification of lipid A gives polymyxin resistance (PubMed:26603172). Confers resistance to polymyxin-type antibiotics; expression of the Mcr-1 protein in E.coli increases colistin and polymyxin B minimal inhibitory concentration (MIC) from 0.5 mg/ml to 2.0 mg/ml. The pHNSHP45 plasmid can transfer efficiently (0.1 to 0.001) to other E.coli strains by conjugation and increases polymxin MIC by 8- to 16-fold; it may not require selective pressure to be maintained in the cell. When transformed into K.pneumoniae or P.aeruginosa it also increases polymxin MIC 8- to 16-fold. In a murine (BALB/c mice) thigh infection study using an mcr1-encoding plasmid isolated from a human patient, the plasmid confers in vivo protection against colistin (PubMed:26603172). This is the first (as of November 2015) reported plasmid-mediated resistance to polymyxin antibiotics; although it does not confer a high MIC it protects against colistin treatment in an infection model. Colistin is one of the last-resort antibiotics available for multidrug-resistant Gram-negative bacteria such as K.pneumoniae, P.aeruginosa and Acinetobacter. First identified from a pig farm in Shanghai, China in July 2013, retrospective screening detects the gene in (slowly) increasing proportions between 2011 and 2015 from pigs and chickens, and also in hospitalized patients in China. Colistin is very widely used in veterinary agriculture (PubMed:26603172). Belongs to the phosphoethanolamine transferase family.