An origin in China seems most probable as antibiotics are widely fed to animals to promote growth. The bulk of the 12,000 tonnes of colistin fed to livestock yearly around the world is used in China, say Liu and colleagues, which would favour the evolution of mcr-1. Antibiotic growth promoters have been banned in Europe precisely because they promote drug-resistant bacteria. Denmark, ironically, was among the first to ban them.
Worldwide concern
The drugs are still heavily used, however, to treat infections common in crowded livestock barns, such as diarrhoea. In 2012, the World Health Organization called colistin critically important for human health, meaning its use in animals should be limited to avoid promoting resistance. Yet in 2013, the European Medicines Agency reported that polymyxins were the fifth most heavily used type of antibiotic in European livestock.
Colistin is used in both humans and animals in India, says Abdul Ghafur of the Apollo Hospital in Chennai. The country is another hotbed of antibiotic resistance because of weak controls on the drugs. “I have treated colistin-resistant infections,” Ghafur says, and researchers in India plan to test bacterial samples for the gene.
“If mcr-1 is present in India then that will be a disaster,” says Ghafur, who fears it will spread as fast as did genes for resistance to another antibiotic of last resort, carbapenem.