A study involving the University of La Laguna has raised concerns about bacteria resistant to carbapenems, last-line antibiotics, and other emerging pathogens in wastewater recycled for agricultural irrigation in four of the Canary Islands where the research was conducted (Lanzarote, Fuerteventura, Gran Canaria, and Tenerife).

Using the One Health approach (a comprehensive strategy recognizing the interdependence of human, animal, and environmental health), 69 bacteria were isolated, including Pseudomonas aeruginosa, Acinetobacter, and Enterobacteriaceae. Of these, 78% were found to be Gram-negative and multidrug-resistant. This means they are resistant to at least three different families of antibiotics designed to eliminate them or inhibit their growth.

The collected sample demonstrates that, although Escherichia coli levels complied with established European regulatory limits, the high presence of other Enterobacteriaceae and the detection of opportunistic pathogens such as Vibrio cholerae, Aeromonas veronii, and A. hydrophila reveal considerable microbial diversity in the reclaimed water used in the Canary Islands. According to the researchers, these findings highlight the problem of using E. coli as the sole indicator of microbiological safety, as it does not reflect the presence of non-fecal environmental pathogens.

The article, published in the journal Microbiology Research, underscores the need to incorporate complementary monitoring parameters. This entails implementing appropriate post-treatment measures to protect public health and agricultural sustainability on water-scarce islands.
Water stress poses a critical challenge for many countries, but especially for isolated regions such as oceanic islands, like the Canary Islands. Desertification, high population density, tourism, insufficient rainfall, water losses in the network, and inadequate management are among the factors contributing to a water demand that exceeds supply. The easternmost Canary Islands experience the greatest water stress, necessitating the use of recycled wastewater in agriculture.

The results of this study demonstrate that this agricultural wastewater can act as a reservoir and amplification site for multidrug-resistant bacteria, particularly carbapenemase-producing strains. Through biofilm formation, storage tanks not only increase the total bacterial load but also promote the transfer of resistance genes. The high proportion of Gram-negative isolates exhibiting carbapenemase-mediated acquired resistance represents a significant public health concern in the context of wastewater reuse.

The researchers highlight the case of Gran Canaria, where the largest number of storage tanks on the island is associated with marked microbiological deterioration and the highest prevalence of carbapenem resistance. This suggests that environmental conditions and management practices can jointly facilitate the spread of resistant microorganisms.
Through the interdependent One Health perspective, on which this study is based, wastewater reuse in agriculture offers significant benefits in water-scarce regions, but presents interconnected risks when hygiene and sanitation measures are insufficient. This research emphasizes the potential transfer of antimicrobial resistance genes and underscores the possibility of contamination and entry into the food chain.

The World Health Organization (WHO) considers bacterial resistance to be one of the main global threats to health due to the alarming increase in infections caused by multidrug-resistant bacteria. Therefore, ensuring safe and sustainable implementation requires strengthening water treatment monitoring 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.

MICROBIOLOGY RESEARCH