The antimicrobial resistance has become one of the main challenges for the public health worldwide, as it makes it difficult to effectively treat infections and increases the risk of serious complications, including death. It is estimated that in 2021 the antimicrobial resistance was associated with 4.71 million deaths worldwide. In this context, a study led by the Barcelona Institute for Global Health (ISGlobal), a center promoted by the ”la Caixa” Foundation, in collaboration with Aigües de Barcelona and carried out in Baix Llobregat (Barcelona), has evaluated the role of wastewater and drinking water treatment plants. in the persistence and spread of bacteria resistant to antibiotics. The results underline the importance of strengthening surveillance of resistant bacteria throughout the entire water cycle and confirm that the water that reaches our homes is completely safe.
The research, carried out during the winter and summer of 2023, analyzed the presence of bacteria resistant to antibioticsas well as resistance genes, in water samples from two treatment plants in the province of Barcelona (Gavà-Viladecans and Baix Llobregat) and one station drinking water treatment of Sant Joan Despí. The research team used a combined approach of metagenomics, cultures and whole genome sequencing to characterize the bacterial diversity in these facilities.
The work, published in the International Journal of Hygiene and Environmental HealthIt is part of the collaboration agreement between ISGlobal and Aigües de Barcelona, started in 2021. With this project, the strategic alliance between both institutions is reinforced, which began with a study on human exposure to nano and microplastics through drinking water.
Almost a thousand strains resistant to antibiotics
The study identified a total of 991 resistant bacterial strains in the water samples analyzed. Of them, the 57.3% they turned out to be multi-resistant and the 2.7% extremely resistant. However, the analysis of the water at the end of the treatment processes revealed a significant reduction in antimicrobial resistance observed in the initial stageswith a minimal presence of resistance genes and absence of strains highly resistant to antibioticswhich shows the effectiveness of treatment plants.
“The reduction was significant in the final phase of the wastewater treatment plants and complete in the water treatment plant, so that the water that reaches our homes is safe,” he points out. Sara M. Sotodirector of the ISGlobal Viral and Bacterial Infections Program and senior author of the study. «However, resistant bacteria from wastewater plants could, upon reaching the environment, transfer their resistance mechanisms to other bacteria. For this reason, all treated wastewater destined for environmental uses or reuse is disinfected, and it is essential to maintain exhaustive control of all processes.»
Therefore, according to the authors of the study, although wastewater treatment plants are essential for reducing fecal load and microbial pathogens, they could also act as reservoirs of antimicrobial resistance. «Our findings expand the understanding of the spread of antimicrobial resistance in aquatic environments and highlight the need to strengthen its surveillance throughout the water cycle, within the framework of the ‘One Health’ approach, which integrates the human, animal and environmental spheres. In addition, the study provides a solid basis for the development of new regulatory frameworks capable of addressing the challenges associated with resistance. antimicrobial,” he points out. Victoria BallenISGlobal researcher and first author of the study.
Main bacteria and resistance genes detected
The most common bacteria found during the early stages of treatment were of the genus Aeromonas (44.3%), followed by Enterobacterales (27.9%), Pseudomonas (19.1%), Acinetobacter (4.8%), shewanella (2.2%) and stenotrophomonas (1%). The Baix Llobregat and Gavà-Viladecans wastewater treatment plants concentrated the majority of the findings, with 531 and 414 strains, respectively, while the Sant Joan Despí drinking water plant recorded only 46 strains. The analysis also showed a marked seasonal variation: more resistant strains were detected during summer (67.8%) than in winter (32.2%).
As for the resistance genesthat is, fragments of the bacteria’s DNA that allow them to survive against antibioticsIt would be found that the most frequent ones conferred resistance to beta-lactamswidely used against common infections; to the aminoglycosidesused in serious infections such as kidney or blood infections; already the macrolidesused in respiratory, skin and soft tissue infections. In addition, resistance genes were found linked to tolerance against biocidesused in disinfectant and cleaning products, as heavy metals.
Another important finding was the detection of 29 strains resistant to colistin (COL)UN antibiotic considered a last resort in serious infections. These strains were found in both the treatment plants and the drinking water plant, with a higher incidence in summer.
Reference
Ballén, V., Gabasa, Y., Castellsagués, L., Alcalde-Rico, M., Pinar-Méndez, A., Vilaró, C., Galofré, B., Soto, SM. Integrated metagenomic, culture-based and whole-genome sequencing analyzes of antimicrobial resistance in drinking and wastewater treatment plants in Barcelona, Spain. International Journal of Hygiene and Environmental Health2025. DOI: 10.1016/j.ijheh.2025.114664
