Researchers have investigated the trend in antimicrobial resistance in the sewage produced in Copenhagen. The results show little fluctuation.
If you want to monitor the trend in antimicrobial resistance in an urban population, the sewers are a good place to start.
The sewers transport our collective faeces, so if anyone has antibiotic-resistant bacteria in their gut, they end up in sewage.
Researchers can collect sewage samples and thus determine whether a population has more or less antibiotic-resistant bacteria over any time scale. They can also determine the trends in resistance to individual antibiotics.
Researchers from the Technical University of Denmark have been investigating this since 2015 by taking weekly samples from the inlets of three main water-treatment plants in Copenhagen. This verified that antimicrobial resistance from 2015 to 2018 was very stable in Denmark’s capital, also week on week.
“We have long aimed to show that the trend in antimicrobial resistance can be monitored by analysing sewage samples. We previously compared antimicrobial resistance in sewage from different parts of the world, and this follow-up study demonstrates that we can determine the antimicrobial resistance trend by taking samples from the same site week after week. However, the results from Copenhagen are not very spectacular, because the antimicrobial resistance in the city’s sewage is very stable,” explains a researcher behind the new study, Frank Møller Aarestrup, Professor and Head of Division, National Food Institute, Technical University of Denmark, Kongens Lyngby.
The research has been published in mSystems.
Analysed sewage for 3,500 antimicrobial resistance genes
The researchers collected sewage samples at least weekly at nonregular intervals for 36 months from the inlets of the three main water-treatment plants in Copenhagen: Avedøre, Damhusåen and Lynetten.
They then analysed the samples for the presence of 3,500 genes resistant to the various kinds of antibiotics.
The researchers extracted the DNA and performed metagenomic sequencing and read-mapping against a database of known antimicrobial resistance genes to determine how many of the known antimicrobial resistance genes were present.
Found traces from an antibiotic-producing factory
There was scarcely any systematic variation across the sites over the 3 years. The antimicrobial resistance in Copenhagen sewage and thereby in the population as a whole seems very stable.
However, the researchers found some local variation between the test sites.
Lynetten had increased resistance to vancomycin. However, the researchers interpret this as not being associated with the development of antimicrobial resistance in the population.
“A producer of vancomycin hydrochloride used to be a few kilometres upstream of the inlet at Lynetten, which probably explains the increase,” says Frank Møller Aarestrup.
Monitoring effect of COVID-19 in sewage
Frank Møller Aarestrup says that even though the results are not headlining Denmark’s media, the ability to validate the research method is important.
The researchers can now monitor the trend in antimicrobial resistance and can therefore also begin to examine how various initiatives in society affect antimicrobial resistance. They can also investigate the time elapsing before the use of new types of antibiotics leads to resistance in sewage.
A relevant example of how to use the method is the ongoing COVID-19 pandemic, during which people have been much more isolated for the past 18 months, with far less antibiotics used.
Children have had fewer ear infections and less pneumonia because they have not been in childcare as much, and the same applies to older people, who have not been exposed to the same degree of infection from various bacteria.
Can the fact that fewer antibiotics have been used be detected in sewage? Future research from the National Food Institute at the Technical University of Denmark will show this.
“We are already conducting a major study on how the pandemic has affected antimicrobial resistance in four cities in Europe. It will be interesting to see whether we can identify such a seismic event as the pandemic and whether the reduced use of antibiotics can be detected in sewage,” explains Frank Møller Aarestrup.
The researchers are also performing other studies examining how demographic differences, such as socioeconomic differences, within the same country affect differences in antimicrobial resistance in sewage.
“We can measure antimicrobial resistance in different parts of the world and over time. Now we need to determine what we can use this for and how to monitor the trends,” concludes Frank Møller Aarestrup.