4) Antibiotic resistance in the water chain: sources, drivers and interventions

Main sources of antimicrobial resistance into the water cycle are human and animal excreta, and antibiotic production sites. They reach water bodies for instance via discharges of (treated) wastewater or agricultural runoff. Concerns are that during treatment or in the environment antimicrobial resistance genes may be transferred and spread to other bacteria, increasing the risks of exposure to resistant pathogenic organisms. A lot of research is going on to gain more knowledge of the potential of gene transfer and risks of antimicrobial resistance. In parallel, multiple solutions are being devised and studied, based in the precautionary principle. Speakers in this session will show different aspects of this problematic.


Søren J. Sørensen, University of Copenhagen:
Horizontal gene transfer between different bacteria is a main driver in the dissemination of antimicrobial resistance genes (ARGs). This way pathogenic bacteria can acquire resistance to multiple antibiotics, an increasing global public health concern. Plasmids are key vectors of horizontal gene transfers shaping bacterial evolution and traits dissemination. Our current knowledge on plasmid transfer and genetic diversity is however to a large extent limited to those able to replicate and maintain in cultivable hosts.  I will present a selection of new culture-independent methods to characterise plasmid encoding ARGs and to study their dissemination in urban water systems. We have developed a targeted metagenomic – metamobilomic  – approach, where only plasmid DNA from complex samples is isolated and sequenced. Using this approach, the potential of the indigenous wastewater microbiome to act as a reservoir for ARGs was investigated. Furthermore, conjugational transfer was tracked, through a well-established dual labelling florescent bioreporter system developed by my group. Our result emphasise that the urban water systems are reservoirs for mobile ARGs and potential hotspots for horizontal gene transfer.

Herman Slijkhuis, DSM Sinochem Pharmaceuticals:
Antimicrobial resistance (AMR) is a large threat to our society. Combating AMR is high on the priority list of many organizations, including the United Nations. Following the 2016 UN General Assembly, many countries drafted  National Action Plans on AMR. However, the execution of these plans remains a big challenge. Antibiotics are widely used as pharmaceutical for humans and animals and via excretion, antibiotics are entering the environment. Next to these streams, manufacturing waste of production sites for antibiotics contribute to the release of antibiotics into the environment. A number of companies producing antibiotics have taken an initiative to set targets limiting discharge containing antimicrobial activity in an Industry Roadmap. DSM Sinochem Pharmaceuticals (DSP) is one company committed to these targets. The targets and how DSP and their peers realize these targets will be discussed. Via its “Sustainable Antibiotics” program, DSP is working on the reduction of the antibiotics in waste streams, not only by its own production sites, but also of companies along its supply chain.

Bert Palsma, STOWA:
Antimicrobial resistance (AMR) is a rapidly expanding problem (a.o. WHO). The occurrence and transfer of AMR are linked to medication, animal husbandry, food, traveling and waste water. In the water sector, logically wastewater treatment plants (WWTP) are a focal point in emission and emission reduction. Policy makers tend to combine reduction of pharmaceutical residues, other micropollutants (e.g. pesticides) and AMR. However, sources and pathways of those pollutants are different and the effectivity of AMR-reduction in surface water by reduction of AMR in WWTP-effluent is therefore uncertain.
Our research showed that the emission of AMR is equally caused by WWTP effluent, combined sewer overflows (CSO) and illicit connections of wastewater sewers to storm water sewers. Exposure and risks related to the emissions of CSO’s and illicit connections could therefore well be higher compared to those of WWTP. Unlike pharmaceutical residues, the reduction and related risks of AMR in surface water seems hard to achieve by reduction of AMR in WWTP-effluent alone.

Rebeca Pallares-Vega, Wetsus & TU Delft:
Antimicrobial resistance (AMR) has been highlighted as one of the biggest health and environmental problems in the present and near future. Wastewater treatment plants (WWTPs), linking human fecal residues and environment have been proposed as of hotspots of the spread of AMR.
Therefore, the presence and removal efficiency of 6 antimicrobial resistance genes (ARGs) and 2 mobile genetic elements (MGEs) in 61 Dutch WWTPs was evaluated by means of qPCR. Possible factors and operational plant parameters that might impact loads of ARGs and MGEs and the removal were gathered and statistically analyzed.
Results showed that all tested genes except korB were, on average, removed to a similar extent (1.8+ log reduction) or better than the total bacteria (measured as 16S rRNA gene). Differences among genes resilience (± 0.8 logs) and plant performances (±0.5-0.7 logs) were observed. Besides, the presence of hospitals or nursing homes did not significantly (p >0.05) changed the concentrations of ARGs or MGEs in the influent and from the extended panel of the operational parameters studied, rainfall most significantly (p <0.01) affected the treatment efficiency by decreasing it.


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