Plasmid-Mediated Colistin Resistance in Animals and Humans in China

Summary and Comment |
November 24, 2015

Plasmid-Mediated Colistin Resistance in Animals and Humans in China

  1. Mary E. Wilson, MD

Colistin resistance has increased in food animals in China; investigators have identified a plasmid-mediated resistance mechanism.

  1. Mary E. Wilson, MD

Polymyxins — polymyxin B and polymyxin E (colistin) — are drugs of last resort in treating multidrug-resistant gram-negative infections. Previously, colistin resistance was attributed to chromosomal mutations and was not known to disseminate widely.

Prompted by an observed increase in colistin resistance in isolates from food animals in China, investigators sought the mechanism. They ultimately identified plasmid-mediated colistin resistance (MCR-1) in Escherichia coli from a pig. Upon screening isolates from five Chinese provinces, they found the mcr-1 gene in 21% of 804 E. coli isolates in pigs at slaughter; in retail meat (22% of pork and 28% of chicken isolates in 2014); and in 1% of 1322 E. coli and Klebsiella pneumoniae clinical isolates from human inpatients in southern China.

Laboratory studies documented the transfer of colistin resistance from one E. coli strain to another and, also, to K. pneumoniae and Pseudomonas aeruginosa. In a murine thigh model, mcr-1 conferred resistance in vivo. The plasmids were stable and persisted in the absence of colistin.

Comment

Given the higher proportion of positive isolates in animals than in humans, the authors postulate that mcr-1–mediated colistin resistance originated in animals and then spread to humans. China is one of the world's highest agricultural users of colistin, but it is also used widely elsewhere, providing selective pressure for resistance to persist. If carbapenemase-producing Enterobacteriaceae strains acquire MCR-1, they will be resistant to all antibiotics. Given the global spread of other types of resistance, such as NDM-1, the authors and the editorialists also expect MCR-1 to spread. Its capacity for transfer to pathogenic E. coli and other gram-negative bacteria could have disastrous consequences. The editorialists call for curtailing use of polymyxins in agriculture, but the problem already appears to be out of the barn.

Editor Disclosures at Time of Publication

  • Disclosures for Mary E. Wilson, MD at time of publication Consultant / Advisory board GeoSentinel Surveillance Network (Special Advisor) Editorial boards UpToDate; Clinical Infectious Diseases; International Health; Infectious Diseases in Clinical Practice; Travel Medicine and Infectious Diseases

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