NEW YORK (GenomeWeb) – A team from the University of Helsinki, the Catholic University of Portugal, and elsewhere has demonstrated that antibiotic resistance genes and mobile genetic elements found at wastewater treatment plants across Europe tend to correspond with the antibiotic use and clinical resistance patterns documented in these regions.
As they reported online today in Science Advances, the researchersused quantitative PCR (qPCR) to search for resistance genes and related mobile genetic elements in untreated raw influent samples and treated final effluent samples from a dozen urban wastewater plants in seven European countries.
Just as clinical antibiotic resistance has been shown to vary along a north-to-south gradient, they found that antibiotic resistance genes turned up more frequently in wastewater treatment site samples from southern countries such as Portugal or Spain, where antibiotics are more widely used, compared to samples from wastewater treatment plants in Norway, Finland, and other northern locations where antibiotic use is believed to be more limited.
"This first trans-Europe surveillance showed that [urban wastewater treatment plant antibiotic resistance] profiles mirror the [antibiotic resistance] gradient observed in clinics," co-senior and corresponding authors Célia Manaia, a researcher at the Catholic University of Portugal's Centre of Biotechnology and Fine Chemistry, and Marko Virta, a microbiologist at the University of Helsinki, and their colleagues wrote.
The results line up with those from a paper published in Genome Research last week, where researchers from the University of Cambridge and elsewhere documented resistance to ampicillin, vancomycin, and other drugs in Enterococcus faecium microbes from untreated water samples collected at municipal wastewater plants and hospital sewer sites in the UK.
For the latest research, Manaia, Virta, and their collaborators set out to assess wastewater treatment site samples within the context of findings from the European Antimicrobial Resistance Surveillance Network, collecting samples from wastewater treatment plants in Spain, Portugal, Cyprus, Ireland, Finland, Norway, and Germany for three days in a row in 2015 or 2016.
After extracting and pooling DNA from samples from each site, the team used almost 400 primer pairs in highly parallel qPCR to profile levels of 229 antibiotic resistance genes, five housekeeping genes, and 25 mobile genetic elements implicated in resistance.
From the antibiotic resistance levels detected, the researchers clustered samples by region, finding a pattern that lined up with antibiotic use and clinical resistance in northern and southern Europe. While aminoglycoside, beta-lactam, tetracycline, and other resistance genes were ubiquitous in the untreated samples, for example, some forms of resistance were enhanced or decreased by location.
"Antibiotic use, environmental temperature, and [urban wastewater treatment plant] size were important factors related with resistance persistence and spread in the environment," the authors reported, noting that their results "highlight the need to implement regular surveillance and control measures, which may need to be appropriate for the geographic regions."
Even so, when they compared the microbes found in treated, outgoing water samples at the European wastewater treatment plants, the researchers found that most drug-resistant bacteria appeared to be removed effectively.
In a statement, Virta noted that "11 of the 12 wastewater treatment plants under investigation mitigated the resistance problem, which seems to indicate that modern plants work well in this regard," but cautioned that "an older plant or otherwise deficient purification process may end up increasing antibiotic resistance in the environment."
"We need more research findings from countries with high antibiotic consumption and less developed wastewater treatment practice," he added.