Scientists in China have found a gene that provides resistance to bacteria against Enterobacteriaceae "last-resort" antibiotics, which could have serious health implications if passed, to other, more dangerous types of bacteria.
Antibiotic resistant germs caused over 2 million illnesses and 23,000 deaths per year, which has led to searches for ways to use fewer antibiotics.
Although researchers might have found a combination of drugs could kill MRSA, researchers at South China Agricultural University say, their finding pointed to a gene passed between more common bacteria such as E. coli, potentially a much larger problem.
In a study on antibiotic resistance of E coli in pigs raised for food, researchers found strains with a polymyxin resistance mechanism, or MCR-1, gene that rendered the drugs ineffective against them.
Polymyxins are considered the last line of defence when other antibiotics prove ineffective.
"The emergence of MCR-1 heralds the breach of the last group of antibiotics," researchers wrote in the study, published in The Lancet: Infectious Diseases.
"There is a critical need to re-evaluate the use of polymyxins in animals and for very close international monitoring and surveillance of MCR-1 in human and veterinary medicine."
The researchers wrote that they had found colistin-resistant bacteria on a Chinese pig farm and later observed the resistant bacteria in raw meat and even humans.
The 50-year-old drug is used mostly on humans, but is given to people only when all other antibiotics had proven ineffective.
The resistant mutation, dubbed the MCR-1 gene, was found in a fifth of the 804 animals observed and also showed up in 15 per cent of the 523 raw meat samples as also in 1 per cent of the 1,332 patients observed in the roughly three-year study.
"The links between agricultural use of colistin, colistin resistance in slaughtered animals, colistin resistance in food, and colistin resistance in human beings are now complete," the researchers wrote.
On the basis of the findings, the researchers have urged countries to reassess their use - and overuse - of antibiotics.
"One of the few solutions to uncoupling these connections is limitation or cessation of colistin use in agriculture," two of the authors wrote in published comments attached to the study.
"Failure to do so will create a public health problem of major dimensions."