The discovery comes at the same time as researchers at the Walter Reed Research Institute in the US identifies the first colistin resistant mcr-1 E.coli in a person.

The colistin resistant E.coli discovered in the pig’s intestine has the same mcr-1 gene.

It was discovered by scientists from the USDA and Department of Health and Human Services searching for colistin-resistant bacteria in food animals, retail meats and people.

The HSS said that the two discoveries are of concern because colistin is used as a last resort drug to treat patients with multi-drug resistant infections.

Healthcare providers are turning to some older antibiotics such as colistin, which was approved in the late 1950s for the treatment of acute and chronic infections, to treat drug-resistant bacterial infections, in situations where commonly used antibiotics are no longer effective.

The discovery follows the first reports from China last November that bacteria containing the mcr-1 gene could be resistant to colistin.

Following the report from China, scientists around the world have been searching for other bacteria containing the mcr-1 gene and bacteria have been found in Europe and Canada.

In May, the Oxford Journal of Antimicrobial Chemotherapy published a report on “Colistin resistance in Salmonella and Escherichia coli isolates from a pig farm in Great Britain”.

The study found that two E. coli and one Salmonella Typhimurium variant Copenhagen were shown to be antibiotic resistant, including resistance to colistin, with one E. coli and the Salmonella carrying the mcr-1 gene.

The study concluded: “Identification of the mcr-1 gene in Enterobacteriaceae from pigs confirms its presence in livestock in Great Britain. The results suggest dissemination of resistance through different horizontally transferable elements.”

Following the discovery of the colistin resistant E.coli in a pig in the US, the USDA is now tracing the sample back to discover the source farm.

The identification of the resistant bacteria in the pig was one out of 949 samples that have been screened to date in a nationwide screening for bacteria containing the mcr-1 gene.

The scientists screening the bacteria found that the mcr-1 carrying colistin resistant E.coli is also resistant to other antibiotics including ampicillin, streptomycin, sulfisoxazole, and tetracycline.

Congresswoman Louise M. Slaughter who has been campaigning for action over antibiotic resistant bacteria and the over use of antimicrobials said following the discovery in the US: “I have been sounding the alarm for years, and now, what we've been dreading has happened.

“We have an antibiotic-resistant superbug that can't be killed by any known drug.

“We need swift, aggressive, global action to stop this in its tracks—now. That starts with passing and implementing one of my top priorities, the Preservation of Antibiotics for Medical Treatment Act.

“If we don’t eliminate the unnecessary and unsafe practice of using 80 per cent of our antibiotics to treat livestock at sub-therapeutic levels, we’ll never get out ahead of this growing public health crisis.”