Reservoirs of resistance

Posted on March 31, 2015   by Benjamin Thompson

When we think about the spread of antibiotic resistance, many of us think of a clinical setting, with its associated hospital-acquired infections, or inappropriate use of drugs. Yesterday at the conference, David Graham, Professor of Environmental Engineering at Newcastle University, described his research looking for other reservoirs of resistance.


David began studying the transmission of and spread of resistance genes in the early 2000s. Initially, he and his colleagues were interested in the use of antibiotics in US agriculture, but in order to understand other drivers of resistance, his group needed to find places in the world that didn’t use the drugs in the same way as the US, which led them to the Almendares River in Cuba.

Although antibiotics are used sparingly in Cuba compared with the US, Graham’s group were still able to identify numerous genes in the river related to antibiotic resistance. The results of this work showed a high correlation between the presence of antibiotic resistance genes and sources of industrial pollution, with increased levels of resistance found near solid waste landfills and pharmaceutical factories.

This work suggested that human activity plays an important role in the broader dispersal and development of resistance, but what role do humans themselves play? To try and answer this question, David travelled to India to take samples from the Ganges, one of the world’s great rivers, which stretches over 1,500 miles from its source in the Himalayas to the Bay of Bengal in Bangladesh.

Specifically, David and Zia S Ahammad, now at the Indian Institute of Technology, Delhi, sampled and studied a reach of the Upper Ganges River, located in the Rishikesh-Haridwar region. Between May and July this pristine region of the river is popular with tourists, seeing the population swell from around 300,000 to over a million. When there is a major pilgrimage to the area, numbers can rise to the tens of millions.

Water samples taken from the river showed that levels of the antibiotic resistant gene NDM-1 were 20 times higher per capita in June than in February. These findings correlated with increased levels of faecal material in the river during June.

While this work identified the presence of the NDM-1 resistance gene, it didn’t identify the species within which it was found. In new research, which David introduced yesterday at the conference, he and his team have isolated a suite of NDM-1 bearing strains from the river, including Escherichia coli and other possible human pathogens. However, it is as yet unknown whether these microbes are present in high enough levels to cause a risk to health.

David suggests that this pattern of resistance genes and microbes in places where large numbers of people congregate is not unique and matches evidence he has gathered from other parts of the world. He is now looking at the cities that people travel from to look for the origin of the genes. As he explains:

“One of the fallacies about antibiotic resistance is that the location you detect it is the location from which it originated. It seems obvious now, but for a long time patients with difficult to treat infections were assumed to have picked up a resistant microbe either locally or from where they’re getting treated.

“It might be that they’ve travelled thousands of miles, or shaken hands with someone who has, and picked up the resistance there. Given the research I’ve done, I think the probability of me having NDM-1 resistant microbes in my gut is higher than most, so it might not be in your best interests to shake my hand after my talk!”

Image: -.-Paul-.- on Flickr, under CC BY-ND 2.0