Antimicrobial resistance can be transferred between bacteria

Thursday 24 May 18


Barth F. Smets
DTU Environment
+45 45 25 22 30


Liguan Li
DTU Environment
+45 45 25 22 90


Professor Søren J. Sørensen,  Department of Biology, University of Copenhagen


tel.: +45 51 82 70 07

Researchers have shown that bacteria can exchange genes across strains. Hopefully, that knowledge can be used to reduce the spread of antimicrobial resistance.

A new study using bacteria from wastewater treatment plants has changed our assumption that the exchange of genes between bacteria only occurs across closely related bacterial strains.

The new findings constitute an important step towards better options for reducing the spread of antibiotic resistance in the future.

“We can demonstrate in the laboratory that bacteria—much more than previously assumed—are capable of exchanging genetic material and thus also their resistance to antimicrobial agents. Where we previously believed that the spread was mainly between closely related species, our studies now show considerable exchange between not so closely related species. The bacteria have a unique ability to cross species barriers—an ability not seen in other organisms. This would be like a rabbit growing wings over just a couple of generations in order to better escape the fox,” explains Professor Søren Sørensen of the Department of Biology, University of Copenhagen, whose research group together with Professor Barth Smets’ research group at DTU Environment is behind the new findings.

“Understanding these unique characteristics of the bacterial communities enables us to better understand antibiotic resistance and thereby also how we can stop the current increase in the spread of multi-resistant bacteria like MRSA, among others”, says Søren Sørensen.

The researchers are, for the first time, following the wastewater on its way from discharge into the sewer until it ends up on the other side of the wastewater treatment plant.

By analysing samples taken from different locations in the wastewater flow from hospital to discharge into water areas, the researchers have been able to identify where and to what extent the bacteria exchange genetic material.

The results underline the importance of future wastewater treatment systems in reducing the spread of antimicrobial resistance. The analyses showed that the ability of the bacteria to transfer genetic material is not weakened on their way from the sewer until they are discharged from the treatment plant, just as it became clear that the bacteria—to a much higher degree than previously believed—are able to transfer genes to bacteria from species other than their closest relatives.

“By marking the genetic elements coding for antimicrobial resistance with a green flourescence marker, we were able to follow them through the wastewater system, and using advanced technology we could simply count how and to what extent the transfers take place. Our findings open up several doors to our understanding of the increased resistance we are currently seeing worldwide, and we can now start to identify how to prevent e.g. wastewater treatment plants from becoming hot spots for the transfer of resistance. With these results, we can demonstrate that antimicrobial resistance genes are incredible survivors, even in environments and under conditions we did not believe possible before. This knowledge is absolutely crucial if we are to reverse the current global ries of antimicrobial resistance,” says Liguan Li of DTU’s research group, who is the main author of the publication describing the new study and its findings.

Future studies to develop guidelines for wastewater treatment
There is still some way to go before the new knowledge can be used to limit the transfer of antibiotic-resistance genes. The next step for the researchers will therefore be to compare the microbial communities from different wastewater treatment types on a larger scale.

"This is not only an important result for us as researchers, but also for the war declared against multi-resistant bacteria."
Professor Barth Smets, DTU Environment

“We will now examine different wastewater treatment plant designs to see if differences in their microbial Communities affect the degree of transfer of genes. The study will cover treatment plants in Denmark, Sweden, England, and Spain and in all countries we will follow the bacteria as they occur, that is from being flushed out the toilet until leaving the water treatment plant and re-entering the circuit.  Against this background, hopefully we will be able to formulate recommendations for the best possible wastewater handling with a view to limiting the spread of antimicrobial resistance,” says Professor Barth Smets.

The current results give cause for optimism among the researchers, as the new knowledge about the ability of bacteria to transfer resistance enables more targeted approaches to combat the growing spread of antimicrobial resistance, which is a world-wide problem.

“This is not only an important result for us as researchers, but also for the war declared against multi-resistant bacteria.” says Barth Smets.

Søren Sørensen adds:

"Our increased understanding of how bacteria adapt to each other and the environment they live in can help us exploit the many beneficial qualities we also find in bacteria to support the next-generation biotechnologies.”