MCR-1 has been detected in samples collected in 2010 and 2011 in Canada. Now scientists are wondering if the superbug gene had made its way into Canada even earlier, and just what that could mean.The Canadian Press
A worldwide hunt by researchers is turning up multiple cases of a new superbug gene, including here in Canada, renewing worries about the spread of drug-resistant bacteria and prompting calls for global action to reduce the use of antibiotics in livestock.
The new gene, called MCR-1, is raising concern because it makes bacteria immune to a group of antibiotics used as the last defence to fight hard-to-treat bugs. The discovery, first reported in November in the British journal The Lancet, was found in bacterial samples from China. But in the weeks since, researchers in several countries have gone back and identified the gene's presence in historical samples, dashing hopes that the first cases were isolated.
The Public Health Agency of Canada confirmed Tuesday that scientists found the gene present in three cases from among 1,600 reviewed – two involving ground beef in Ontario in 2010 and one involving an Ottawa woman in 2011.
Matthew Gilmour, the scientific director of the agency's Winnipeg lab, said the hunt is continuing in past cases, and the lab will now screen for the gene and has created tests that will be sent to provincial labs so they can do likewise.
Dr. Gilmour said he is not aware of any evidence of the gene in current cases. The worry is that it will show up in cases involving infections that are resistant to most antibiotics – making them resistant to last-resort antibiotics such as colistin, an old drug that was rarely used on humans because of its toxicity, but is increasingly given when all other treatments fail.
"You might have nothing available to treat an infection. That is the big worry," he said.
For scientists studying drug resistance, the findings are the latest example of what they have been saying for years – that unless steps are taken to curb the unnecessary use of antibiotics, particularly in healthy livestock, the effectiveness of these life-saving drugs will be greatly diminished. The widespread nature of the discoveries also underlines the global effort that will be required to make progress, they say.
Bob Hancock, a Canada Research Chair at the University of British Columbia, is a specialist in the group of antibiotics called polymyxins – the drugs, including colistin, to which the newly discovered gene makes bacteria resistant.
What is especially troubling about the new findings is the nature of the resistance, he said. It is carried on a plasmid, what Dr. Hancock described as a circle of DNA that can easily transmit from one organism to another to spread the resistance.
As an example, he pointed to the use of tetracycline, which was widespread in the 1960s. But in Japan, drug resistance rose from zero to 60 per cent in about four years because of the same kind of plasmid-mediated resistance.
"That's the kind of thing that we are now concerned about," he said. "It is a big deal. It's not like the end of antibiotics, but it is a big deal."
Researchers in more than a dozen countries have now reported the presence of this resistance, he said, but it is not yet clear how easily it is transmitted.
Gerry Wright, a microbiologist at McMaster University in Hamilton, likens the spread of drug-resistant bacteria to climate change, a creeping problem that can't be solved by the actions of one nation.
"We've got ourselves in the situation where we have now let this genie out of the bottle and it is probably going to have a significant impact – if not today then in years to come – in our ability to treat infectious disease in humans," he said. "We have to get our act together across the world in order to deal with this."
Dr. Wright said one concrete measure, taken by the European Union, would be to stop the large-scale use of antibiotics, including colistin, on livestock to support intensive farming and encourage growth, rather than to treat sick animals.
At the same time, developing new antibiotics has proved difficult.
Dr. Wright said the existence of the gene will not affect healthy people. But for those who are in hospital or undergoing treatments such as cancer therapy, it represents another risk. "No good can come of this," he said.