Integrated antibiotic resistance (AR) surveillance is one of the objectives of the World Health Organization global action plan on antimicrobial resistance. Urban wastewater treatment plants (UWTPs) are among the most important receptors and sources of environmental AR. On the basis of the consistent observation of an increasing north-to-south clinical AR prevalence in Europe, this study compared the influent and final effluent of 12 UWTPs located in seven countries (Portugal, Spain, Ireland, Cyprus, Germany, Finland, and Norway). Using highly parallel quantitative polymerase chain reaction, we analyzed 229 resistance genes and 25 mobile genetic elements. This first trans-Europe surveillance showed that UWTP AR profiles mirror the AR gradient observed in clinics. Antibiotic use, environmental temperature, and UWTP size were important factors related with resistance persistence and spread in the environment. These results highlight the need to implement regular surveillance and control measures, which may need to be appropriate for the geographic regions.

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To test the hypothesis of a seasonal relationship of antibiotic prescriptions for outpatients and the abundance of antibiotic resistance genes (ARGs) in the wastewater, we investigated the distribution of prescriptions and different ARGs in the Dresden sewer system and wastewater treatment plant during a two-year sampling campaign. Based on quantitative PCR (qPCR), our results show a clear seasonal pattern for relative ARGs abundances. The higher ARGs levels in autumn and winter coincide with the higher rates of overall antibiotic prescriptions. While no significant differences of relative abundances were observed before and after the wastewater treatment for most of the relative ARGs, the treatment clearly influenced the microbial community composition and abundance. This indicates that the ARGs are probably not part of the dominant bacterial taxa, which are mainly influenced by the wastewater treatment processes, or that plasmid carrying bacteria remain constant, while plasmid free bacteria decrease. An exception was vancomycin (vanA), showing higher relative abundance in treated wastewater. It is likely that a positive selection or community changes during wastewater treatment lead to an enrichment of vanA. Our results demonstrate that in a medium-term study the combination of qPCR and next generation sequencing corroborated by drug-related health data is a suitable approach to characterize seasonal changes of ARGs in wastewater and treated wastewater.

Integrons are extensively targeted as a proxy for anthropogenic impact in the environment. We developed a novel high-throughput amplicon sequencing pipeline that enables characterization of thousands of integron gene cassette-associated reads, and applied it to acquire a comprehensive overview of gene cassette composition in effluents from wastewater treatment facilities across Europe. Between 38 100 and 172 995 reads per-sample were generated and functionally characterized by screening against nr, SEED, ARDB and β-lactamase databases. Over 75% of the reads were characterized as hypothetical, but thousands were associated with toxin-antitoxin systems, DNA repair, cell membrane function, detoxification and aminoglycoside and β-lactam resistance. Among the reads characterized as β-lactamases, the carbapenemase bla was dominant in most of the effluents, except for Cyprus and Israel where bla was also abundant. Quantitative PCR assessment of bla and bla genes in the European effluents revealed similar trends to those displayed in the integron amplicon sequencing pipeline described above, corroborating the robustness of this method and suggesting that these integron-associated genes may be excellent targets for source tracking of effluents in downstream environments. Further application of the above analyses revealed several order-of-magnitude reductions in effluent-associated β-lactamase genes in effluent-saturated soils, suggesting marginal persistence in the soil microbiome.

Antibiotic resistant bacteria and antibiotic resistance genes (ARGs) are major human-health threats, widely distributed in the environment. Quantitative PCR (qPCR) is a standard approach to detect and quantify ARGs in environmental compartments. However, the comparison of gene quantification reported by different laboratories is challenging since data are predominantly obtained under nonharmonized conditions, using different qPCR protocols. Objectives The aim of this study was to develop and calibrate standardized qPCR procedures for quantification of key ARGs, analyzing the same samples with common protocols and distinct equipment, reagents batches and operators. Methods Treated wastewater from three European countries were processed immediately after collection and transported to the laboratory for total DNA extraction. DNA extracts from each sample were pooled and aliquots were distributed by five partners involved in the calibration procedure. The genes 16S rRNA, vanA, blaTEM, qnrS, sul1, blaCTXM-32 and intI1 were analyzed using harmonized qPCR protocols and the constructed pNORM1 plasmid, which contains fragments of the seven targeted genes, was used for generating standard curves. Conclusions The 16S rRNA gene was the most abundant, followed by sul1, intI1, qnrS and blaTEM. Quantifications made by different partners were reproducible and inter-laboratory variation was < 20%. The notorious exception was for the qnrS gene, and therefore protocol improvement is recommended. The genes blaCTXM-32 and vanA were below the limit of quantification in most or all of the samples analyzed. The inter-laboratory calibration is an adequate approach to reliably assess ARG abundance and environmental contamination in different environments and geographic locations.