(HealthDay News) — A new plasmid-mediated polymyxin resistance mechanism, MCR-1, has emerged in Enterobacteriaceae, according to a study published online Nov. 18 in The Lancet Infectious Diseases.

Yi-Yun Liu, from the South China Agricultural University in Guangzhou, and colleagues used whole plasmid sequencing and subcloning to identify the mcr-1 gene in Escherichia coli strain SHP45. Sequence comparisons, homology modeling, and electrospray ionization mass spectrometry were conducted. The prevalence of mcr-1 was assessed in E. coli and Klebsiella pneumoniae strains from five Chinese provinces. In a murine thigh model the authors examined the ability of MCR-1 to confer polymyxin resistance in vivo.

The researchers found that polymyxin resistance was solely attributable to the plasmid-mediated mcr-1 gene. The mcr-1-carrying plasmid was mobilized to an E. coli recipient by conjugation and was maintained in K. pneumoniae and Pseudomonas aeruginosa. Production of MCR-1 negated the efficacy of colistin in an in-vivo model. Expression of MCR-1 in E. coli resulted in the addition of phosphoethanolamine to lipid A. The researchers observed mcr-1 carriage in E. coli isolates collected from 15 percent of raw meat samples and 21 percent of animals during 2011 to 2014, and in 1 percent of 1,322 samples from inpatients with infection.

“The emergence of MCR-1 heralds the breach of the last group of antibiotics, polymyxins, by plasmid-mediated resistance,” the authors write. “Our findings emphasize the urgent need for coordinated global action in the fight against pan-drug-resistant Gram-negative bacteria.”

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