During the COVID-19 pandemic, the world has become aware of the value of using sewage analyses to monitor disease development in an area. However, at DTU National Food Institute, a group of researchers has been using sewage monitoring from throughout the world since 2016 as an effective and inexpensive tool for monitoring infectious diseases and antimicrobial resistance.

By analysing sewage samples received by DTU from 243 cities in 101 countries between 2016 and 2019, the researchers have now mapped where in the world the occurrence of resistance genes is highest, how the genes are located, and in which types of bacteria they are found.

The results from the new metagenomic study — which have just been published in Nature Communications — have surprised the researchers. In fact, the study shows that the genes have appeared in many different genetic contexts and bacterial types, indicating greater transmission than the researchers had expected.

“We’ve found similar resistance genes in highly different bacterial types. We find it worrying when genes can pass from a very broad group of bacteria to a completely different group with which there is no resemblance. It’s rare for these gene transmissions to occur over such long distances. It’s a bit like very different animal species producing offspring,” explains Assistant Professor Patrick Munk.

If the genes are in bacteria that don’t usually make people sick — such as lactic acid bacteria — it’s of less concern. However, if the resistance genes find their way into bacteria that are important to human health — such as salmonella — it’s a completely different story.

“This makes it much more likely that the bacteria will actually kill people — for example in a hospital — because no treatment is available,” emphasizes Patrick Munk.

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