David Cameron

British Prime Minister David Cameron called on Group of Seven leaders to fight superbugs as their summit wrapped in Ise Shima, Japan, on Friday. (Carlos Barria/Reuters)

The nightmare scenario of untreatable infections isn't a reality, yet, but it is an evolving situation of concern to doctors and public health officials worldwide.

On Friday, British Prime Minister David Cameron urged G7 leaders meeting in Japan to do more to fight superbugs. His comments followed the first U.S. report of a patient infected with bacteria resistant to a last-resort antibiotic called colistin.

The 49-year-old woman's urinary tract infection was successfully treated with other antibiotics, and she recovered.  

"In too many cases antibiotics have stopped working," Cameron said, calling on countries to stem resistance by reducing the use of antibiotics and rewarding drug companies for developing new medicines.

In January, the BC Centre for Disease Control confirmed a case of MCR-1 resistance in an individual who returned to the province from China. MCR-1 is a gene that makes E. coli and some other species of bacteria resistant to colistin. That patient was also successfully treated and discharged. 

E. coli bacteria

Colonies of E. coli bacteria grown on a plate. U.S. health officials reported the first case in the country of a patient with E. coli bacteria carrying the mcr-1 gene, an infection resistant to colistin, an antibiotic of last resort. (CDC/Reuters)

When scientists went back to test Canadian samples, an Ottawa patient was also found to be a carrier for bacteria with resistance to colistin, but that wasn't what had made her sick. Again, the infection was successfully treated. It was the country's first documented finding of the resistance gene in a human. 

Most bacteria that carry the MCR-1 gene can still be treated by other, more commonly used antibiotics. But resistance to colistin is a concern because it is often the last-resort treatment for multidrug-resistant bacteria. It's held in reserve because it's so toxic to the kidneys

As Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, told reporters after the U.S. publication of the first report of MCR-1 in the U.S: "It is the end of the road for antibiotics unless we act urgently."

Cameron's incentives to develop new antibiotics could pave new routes. In January, 83 companies, including pharmaceutical companies Pfizer, Merck & Co., Johnson & Johnson and GlaxoSmithKline, signed a declaration urging governments to support work on new antibiotics.

Part of the problem is where the MCR-1 gene itself is. It can be found on a plasmid — a piece of DNA that bacteria can easily swap. Given that ease of spread, the fear is the gene will make its way to bacteria that are resistant to other antibiotics, resulting in an untreatable infection like those in the pre-antibiotic era.

We're not there.

But microbiologists have long called for the use of antibiotics in agriculture to be abandoned. The call has grown louder in Canada since the publication last year of the Canadian Antimicrobial Resistance Surveillance Report showing that in 2013 (the most recent year for which data are available), about 1.4 times more antimicrobials were distributed for use in animals than in humans in Canada. 

This week, the European Medicines Agency proposed to minimize sales of colistin for use in animals and restrict its use in animals to last resort only. 

As doctors, scientists and farmers work to conserve antibiotics for surgical and other vulnerable patients, there are also unanswered scientific questions.  

The U.S. patient reported no travel history in the previous five months, so doctors aren't sure how she acquired MCR-1 resistant bacteria, which was originally discovered in pigs, pork and a small number of people in China. It has since been found in food and humans in Europe and South America.

The U.S. and Canadian researchers have said the true prevalence of MCR-1 in the population needs to be determined, and continued surveillance is critical. 

With files from CBC News, Associated Press and Reuters