A new gene that makes bacteria extremely resistant to last-resort antibiotics has been detected by Chinese scientists in people and pigs, including in strains exhibiting epidemic potential.

Published in the journal Lancet Infectious Diseases, the gene mcr-1 – which enables bacteria to be highly resistant to polymyxins or “the last line of antibiotic defense” left – was found widespread in Enterobacteriaceae samples from south China patients and pigs.

The gene was detected in plasmids, which are mobile DNA easily replicated and transferred from one bacteria to another. This raises the alarming concern of it potentially spreading and diversifying between various bacterial groups.

Study author Prof. Jian-Hua Liu of South China Agricultural University dubbed the results “extremely worrying” as polymyxins colistin and polymyxin B were the last class of antibiotics where resistance was unable to spread from cell to cell.

Unlike in colistin resistance stemming from chromosomal mutations, the first polymyxin resistance gene is quickly transferred between typical bacteria E. coli and Klesbsiella pneumoniae. “[This is] suggesting that the progression from extensive drug resistance to pandrug resistance is inevitable,” warned Liu.

The mcr-1 gene was found widespread in E.coli isolates from animal and raw meat samples, with the positive samples increasing every year. The gene was also found in 16 bacteria isolates from 1,322 hospital patients.

Between E. coli strains, the transfer rate or at which the gene was copied and transferred between several bacteria was discovered to be very high. The gene, too, was seen likely to spread fast into pathogenic bacteria in humans.

In response to the rapid rise in colistin-resistant bacteria – called by the researchers “the breach of the last group of antibiotics” – the agriculture ministry of China had started to assess colistin’s use in animal feed additives.

In 2010, the superbug gene NDM-1 made headlines as well, emerging in India and rapidly spreading in different parts of the world.

China remains one of the world’s biggest users and producers of colistin for agricultural and veterinary purposes. In Europe, a glaring 80 percent of polymyxin sales – mostly colistin – are in Germany, Italy, and Spain.

Worldwide, the demand for this antibiotic class in agriculture is estimated to reach nearly 12,000 tons annually by the end of this year. It will climb to 16,500 tons by 2021, stated by a QYResearch Medical Research Center report.

Infectious diseases specialist Dr. Bruce Hirsch from New York’s North Shore University added warnings that resistance to polymyxin antibiotics had been previously rare. Now, he said, the new resistance gene is bringing humanity “closer to a future ‘pre-antibiotic’ era” where there are very few options to fight life-threatening bacterial infections.

"If you don't need antibiotics, don't take them. You are only giving bacteria extra practice," Dr. Hirsch advised.

Photo: U.S. Department of Agriculture | Flickr

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