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 The discovery was described as "alarming" by scientists, who
called for urgent restrictions on the use of polymyxins - a class of
antibiotics that includes the drug colistin and is widely used in
livestock farming.
"All use of polymyxins must be minimized as soon as possible and all
unnecessary use stopped," said Laura Piddock, a professor of
microbiology at Britain's Birmingham University who was asked to
comment on the finding.
Researchers led by Hua Liu from the South China Agricultural
University who published their work in the Lancet Infectious
Diseases journal found the gene, called mcr-1, on plasmids - mobile
DNA that can be easily copied and transferred between different
bacteria.
This suggests "an alarming potential" for it to spread and diversify
between bacterial populations, they said.
 The team already has evidence of the gene being transferred between
common bacteria such as E.coli, which causes urinary tract and many
other types of infection, and Klesbsiella pneumoniae, which causes
pneumonia and other infections.
This suggests "the progression from extensive drug resistance to
pandrug resistance is inevitable," they said.
"(And) although currently confined to China, mcr-1 is likely to
emulate other resistance genes ... and spread worldwide."
INDIAN PRECEDENT
The discovery of the spreading mcr-1 resistance gene echoes news
from 2010 of another so-called "superbug" gene, NDM-1, which emerged
in India and rapidly spread around the world.
Piddock and others said global surveillance for mcr-1 resistance is
now essential to try to prevent the spread of polymyxin-resistant
bacteria.
China is one of the world's largest users and producers of colistin
for agriculture and veterinary use.
Worldwide demand for the antibiotic in agriculture is expected to
reach almost 12,000 tonnes per year by the end of 2015, rising to
16,500 tonnes by 2021, according to a 2015 report by the QYResearch
Medical Research Center.
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In Europe, 80 percent of polymixin sales - mainly colistin - are in
Spain, Germany and Italy, according to the European Medicines
Agency's Surveillance of Veterinary Antimicrobial Consumption
(ESVAC) report.
For the China study, researchers collected bacteria samples from
pigs at slaughter across four provinces, and from pork and chicken
sold in 30 open markets and 27 supermarkets in Guangzhou between
2011 and 2014. They also analyzed bacteria from patients with
infections at two hospitals in Guangdong and Zhejiang.
They found a high prevalence of the mcr-1 gene in E coli samples
from animals and raw meat. Worryingly, the proportion of positive
samples increased from year to year, they said, and mcr-1 was also
found in 16 E.coli and K.pneumoniae samples from 1,322 hospitalized
patients.
David Paterson and Patrick Harris from Australia's University of
Queensland, writing a commentary in the same journal, said the links
between agricultural use of colistin, colistin resistance in
slaughtered animals, colistin resistance in food, and colistin
resistance in humans were now complete.
"One of the few solutions to uncoupling these connections is
limitation or cessation of colistin use in agriculture," they said.
"Failure to do so will create a public health problem of major
dimensions."
(Reporting by Kate Kelland)
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