Study Warns of Multidrug-Resistant Bacteria in Canary Islands' Reclaimed Irrigation Water

Using treated wastewater for farming in the Canary Islands faces a significant technical hurdle. A recent study published in the journal Microbiology Research, featuring researchers from the University of La Laguna (ULL), suggests that current safety checks may not be enough to detect multidrug-resistant bacteria and other emerging pathogens in irrigation water.

The study analyzed water samples from Lanzarote, Fuerteventura, Gran Canaria, and Tenerife. Researchers identified 69 bacterial strains, noting that these water sources can act as breeding grounds for microorganisms resistant to carbapenems—powerful antibiotics typically reserved for treating severe hospital infections. This discovery highlights the importance of the "One Health" approach, a global strategy that connects human, animal, and environmental health, especially as the World Health Organization warns of the rising threat of antimicrobial resistance.

A key issue identified by the study is that current European regulations rely too heavily on Escherichia coli as the main indicator of water quality. Researchers argue that this marker is insufficient, as it does not guarantee the absence of other dangerous pathogens or clinically relevant bacteria, such as Aeromonas.

The study also found significant differences between the islands. Gran Canaria showed the highest levels of resistant bacteria, suggesting that water quality is affected not just by the treatment process, but also by how the water is stored and distributed. Poorly maintained reservoirs can lead to the buildup of biofilms, which allow bacteria to thrive and share resistance genes. In contrast, Tenerife, which often distributes water more directly from treatment plants, showed lower levels of contamination.

The authors are not suggesting that the use of reclaimed water should stop—it remains essential for the islands, which face constant water shortages. Instead, they are calling for an update to safety protocols. They recommend expanding the range of microbiological tests and improving distribution networks to prevent these resistance genes from entering the food chain. Ultimately, the study emphasizes that for irrigation with treated water to be sustainable, it requires stricter oversight that monitors the entire system, from the treatment plant to the farm.