A study in which the University of La Laguna has participated detects the presence of multidrug-resistant bacteria to antibiotics in recycled wastewater for agricultural irrigation in Lanzarote, Fuerteventura, Gran Canaria, and Tenerife.
Despite the fact that the use of recycled water is important for combatting water scarcity of islands like Lanzarote, the public university warns that it presents risks if hygienic measures and sanitary "are not sufficient". The research indicates that antimicrobial resistance genes can be transferred and that this can generate contamination and the entry of these bacteria into the food chain.
78% of bacteria multi-resistant to antibiotics
The finding exposes the presence of bacteria that resist last-line antibiotics. In this research, the scientists relied on the integral strategy of human-animal-environmental health interdependence, known as the One Health. approach. For this, they isolated 69 bacteria, among which are Pseudomonas aeruginosa, Acinetobacter and Enterobacteriaceae. In total, they discovered that 78% were multidrug-resistant to antibiotics, that is, capable of surviving against a minimum of three different families of antibiotics, designed to eliminate them or inhibit their growth.
The collected sample shows that the levels of Escherichia coli comply with the established European regulatory limits, while the presence of other bacteria such as Enterobacteriaceae and other opportunistic pathogens such as Vibrio cholerae, Aeromonas veronii and A. hydrophila evidences "a considerable microbial diversity" in the regenerated water used in the Canary Islands.
These findings, according to the researchers, highlight that using the presence of E.coli as the sole indicator parameter of microbiological safety does not truly reflect the range of pathogens that can be found in recycled wastewater for agricultural use.
The research supports the use of more parameters to monitor
The article “A One Health perspective: Occurrence study of carbapenem-resistant bacteria and other emerging pathogens from recycled wastewater used in agriculture”, published in the journal Microbiology Research and in which María Martínez-Ruíz, researcher from the Department of Obstetrics and Gynecology, Pediatrics, Preventive Medicine and Public Health, Toxicology, Legal and Forensic Medicine and Parasitology of the University of La Laguna, participates, highlights the need to incorporate complementary parameters for monitoring.
This involves applying adequate post-treatment measures to protect public health and agricultural sustainability on islands with water scarcity.
The water stress that demands more wastewater
Water stress constitutes a critical challenge for numerous countries, but especially isolated regions such as oceanic islands, such as the Canary Islands. Desertification, high population density (278.77 inhabitants/km²), tourism (17.77 million tourists in 2024), insufficient rainfall, water losses in the network, or inadequate management are among the factors that contribute to a water demand that exceeds supply. The easternmost islands of the Canary Islands present the greatest water stress, which requires the use of recycled wastewater in agriculture.
The results of this study demonstrate that this wastewater for agricultural use can act as a reservoir and amplification site for multi-resistant bacteria, particularly carbapenemase-producing strains.
A "significant health concern"
Storage tanks, through the formation of biofilms, not only increase the total bacterial load but also favor the transfer of resistance genes. The high proportion of gram-negative isolates that present acquired resistance mediated by carbapenemases represents a significant concern for public health in the context of wastewater reuse.
The researchers highlight the case of Gran Canaria, where the largest number of storage deposits on the island is associated with a marked microbiological deterioration and the highest prevalence of carbapenem resistance. This suggests that environmental conditions and management practices can jointly facilitate the dissemination of resistant microorganisms.
Through the interdependent perspective One Health, on which this study is based, the reuse of wastewater in agriculture offers important benefits in regions with water scarcity, but presents interconnected risks when hygienic-sanitary measures are not sufficient. This research highlights the possible transfer of antimicrobial resistance genes and underscores the possibility of contamination and entry into the food chain.
Finally, the Canarian university has indicated that the World Health Organization (WHO) considers bacterial resistance as one of the main global threats to health due to the alarming increase in infections caused by multi-resistant bacteria. For this reason, it has requested that a safe implementation and sustainable one requires strengthening surveillance of water treatment and improving storage and management practices. These integrated measures, according to the research team, are essential to protect environmental integrity, food safety, and public and animal health.
