Foto: Joachim Rode

WASTEWATER EXAMINED: Experimental idea may prevent resistance from spreading

Friday 18 Sep 20


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


Arnaud Dechesne
Senior Researcher
DTU Environment
+45 45 25 22 91

Did you know...

Several infections—e.g. pneumonia, tuberculosis, gonorrhoea, and salmonella—are becoming harder to treat as antibiotics lose their effectiveness.
Source: WHO

Analysis from four countries shows that bacteria can become ‘infected’ with antibiotic resistance in wastewater treatment plants. However, it may be possible to limit ‘infection’ by exploiting nature’s bacteria killers in the plants.

This article contains one good piece of news—and two bad pieces. First, the bad news: Recent research confirms that antibiotic resistance can spread in wastewater treatment plants. Researchers from DTU Environment are completing a project with wastewater analyses from four countries: Spain, Israel, the UK, and Denmark.  The analyses support the results of an earlier and smaller project where resistance dispersion in Danish wastewater was detected.

“In the new analyses we find consistency with the results of our first project, including the type of bacteria that pick up resistance in treatment plants and the extent of this resistance transfer.  This means that what we found in Danish wastewater wasn’t some random mechanism, but rather a bigger and more general problem,” says Professor Barth F. Smets from DTU Environment who led the research project.

Mobile resistance DNA

The resistant bacteria end up in the wastewater because everything we flush down the toilet ends up here—also the resistant bacteria we may be carrying—e.g. following penicillin treatment or hospitalization. As it turns out, most human-resistant bacteria do not survive long in wastewater. Nevertheless, the bacteria are insidious, as the genes that make them resistant are found on some mobile molecules called plasmids. The mobility of plasmids is the reason why antimicrobial resistance can be transmitted from one microorganism to another—and this is what happens in the treatment plants. The plasmids more or less attach themselves to a new bacterium in the wastewater, which thus becomes resistant. The new resistant bacteria are often bacteria that occur naturally in the environment, and suddenly we have resistant bacteria that can perform well in our surroundings.

“This is worrying because we risk spreading resistance further if the bacteria then show up in the water we drink, swim in, or water our crops with,” says Barth F. Smets.

Bad news number two

The researchers discovered another piece of bad news along the way: the bacteria appear to hold onto the resistance genes even though they do not need them.  Until now, there has been a widespread belief that bacteria expend more energy carrying the extra DNA, so as soon as they do not need it—i.e. when they are in an environment where they do not encounter antibiotics—they will uncouple the DNA. Apparently, this is not the case.

“We examined bacteria that we had made resistant, after which we ensured that there were no antibiotics in their environment. We found several bacteria that still retain their resistance genes even if they don’t need them. This means that the resistance agents are not transient as we thought or that there are other mechanisms that make the bacteria appear to have an advantage in holding on to the resistance genes,” says Barth F. Smets.

The good news

Despite the gloomy findings in the wastewater studies, this knowledge still offers hope.

“Once we know how resistance spreads, we can begin finding solutions that can limit it,” says Barth F. Smets.

The professor’s colleague at DTU Environment—Senior Researcher Arnaud Dechesne—has a possible solution. The idea was so different that he was supported by Villum Fonden’s Experiment programme, which funds wild and experimental research. “I want to use nature to fight nature,” Arnaud Dechesne begins, explaining his idea.

In nature, bacteria have a natural enemy—the bacteriophage. “It’s a virus that infects and takes over bacteria and then exploits them to replicate itself. The bacterium dies in the process.” According to the associate professor, bacteriophages have long been a source of medical interest. But where the focus here has been to find one bacteriophage that can kill one type of bacterium, Arnaud Dechesne is looking for bacteriophages that can attack several kinds of bacteria. They must, however, have one thing in common:

“The bacteria must all carry plasmids. I want to find bacteriophages that can spot these bacteria, as it’s in the plasmids that the resistance DNA is located. With these bacteriophages, we will be able to eradicate resistant bacteria in wastewater treatment plants,” says Arnaud Dechesne.

These bacteriophages are found in nature, so the senior researcher’s task is ‘simply’ to find them, isolate them, and test whether they are fit for purpose.

“If we can show in the lab that bacteriophages can detect and destroy bacteria with plasmids, then maybe one day we can harness that knowledge by implementing bacteriophages in wastewater treatment plants,” says Arnaud Dechesne.

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26 JANUARY 2021