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Antimicrobial resistance

Gene discovered in China that is making bacteria resistant to ‘last resort’ antibiotics

Researchers find gene in humans and animals that shows resistance to polymyxin antibiotics.

A gene found in pathogenic bacteria, known as mar-1, was found in plasmids, mobile DNA that can transfer resistance between Escherichia coli (E coli) strains. In the image, micrograph of E coli bacteria

Source: CNRI / Science Photo Library

Strains of Escherichia coli (E coli; pictured) can transfer antibiotic resistance through mobile DNA known as plasmids

A gene found in pathogenic bacteria that controls resistance to an essential group of antibiotics called polymyxins has been found in hospital patients, pigs and chickens, researchers have reported. 

The gene, known as MCR-1, was found in plasmids, which are mobile DNA that can transfer resistance between bacteria. 

This resistance differs from that already known to polymyxins – which include colistin, an antibiotic used to treat Gram-negative infections where other antibiotics have not been effective. Previous examples of colistin resistance have not spread outside hospitals because the genes have generally been unstable and not transmissible between bacteria. 

The findings – published in The Lancet Infectious Diseases[1] on 18 November 2015, by Yi-Yun Liu of the South China Agricultural University in Guangzhou, China and colleagues – are alarming because they describe widely transmissible plasmid-mediated colistin resistance for the first time. 

The researchers found that the plasmid that bears the colistin resistance mechanism was easily passed between Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa strains, including strains with known epidemic potential. The plasmids were stable, so in the absence of selection pressure by colistin, the plasmids would be maintained. They found the resistant gene in pigs and meat sold in China, as well as in bacterial samples analysed in hospital patients. 

Awa Aidara-Kane, coordinator for foodborne and zoonotic diseases at the World Health Organization (WHO), says the findings are worrying. “Colistin [is a drug] of last resort for life-threatening infections. Medical doctors do not like to use colistin because of its toxicity, so using it is already a signal of lack of alternatives,” she says. “We are in deep trouble medically if even colistin with all its toxicity is not there as a last resort.” 

The research suggests that the links between agricultural use of colistin and colistin resistance in slaughtered animals, food and human beings are now complete, Aidara-Kane says. 

China is the world’s largest poultry and pig supplier – Liu’s team report it produced 17.5 million tonnes and 56.7 million tonnes of meat in 2014, respectively.  Although most of this production is for domestic consumption, 10% — which still approaches millions of tonnes — is for export. The country is also one of the world’s highest users of colistin in agriculture. Colistin is used in animal feed additives.

“To avert the spread, the solution is to limit or cease agricultural use of antimicrobials (including colistin) that are critically important for human health,” Aidara-Kane concludes. With the globalisation of travel, food and trade it is likely that this problem occurs well beyond China, she adds. 

Global demand for colistin in agriculture is expected to reach 11,942 tonnes per annum by the end of 2015, writes Liu’s team. 

The news comes during the WHO’s World Antibiotic Resistance Awareness Week (16–22 November 2015). The researchers note that the WHO, in its 2012 advisory group on integrated surveillance of antimicrobial resistance, concluded that colistin should be listed under those antibiotics of critical importance. “It is regrettable that in the 2014 Global Report on Surveillance, the WHO did not list any colistin-resistant bacteria as part of their ‘selected bacteria of international concern’.”

Citation: The Pharmaceutical Journal DOI: 10.1211/PJ.2015.20200128

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Supplementary images

  • A gene found in pathogenic bacteria, known as mar-1, was found in plasmids, mobile DNA that can transfer resistance between Escherichia coli (E coli) strains. In the image, micrograph of E coli bacteria

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