Juan Navedo, academic of the PhD in Marine Biology and PhD in Ecology and Evolution of the Faculty of Sciences of the Universidad Austral de Chile (UACh), found, through research, a strong presence of antibiotics in the coastal wetlands of the island of Chiloé, evidencing the widespread presence of bacteria resistant to these drugs that endanger wildlife on a global scale and the treatment of diseases in both animals and humans. "Seven antibiotics from different families, three of them used exclusively in the salmon industry, were studied in two bays in Chiloé: the first, to the north in the Chacao channel, 30 km from the nearest marine farming center; and the second, near the Dalcahue channel, surrounded by marine farming centers," explained Navedo, a researcher at the Institute of Marine and Limnological Sciences of the Faculty of Sciences of the Austral University. The results obtained showed that 62% of the sediment samples, considering both bays, had resistant bacteria and resistance genes to at least one antibiotic, while only in the area closest to the cultivation centers were multi-resistant bacteria found. "To produce a kilo of salmon in Chile, 100 times more antibiotics are used than in Norway, which is the world's leading producer of this product. This volume of drugs reinforces the idea that the antibiotic footprint must be widely extended in the coasts of southern Chile and may even reach North America, through migratory birds, affecting multiple components of biodiversity, including human beings", denounces the academic, while calling on the Chilean government to increase regulations for this industry. (Read news in El Mostrador).
The migratory shorebird known as the "straight-billed curlew"(Limosa haemastica) travels 15,000 kilometers each year from the coastal wetlands of Chiloé to Alaska to spend its breeding season in the northern hemisphere. To carry out this journey, it must make a preparation that includes physiological adaptations that allow it to fly for seven consecutive days to the wetlands of the Great Plains of North America, its only stopover 10,000 kilometers from Chiloé.
Among these adaptations, this bird doubles its weight and reduces the size and functionality of organs that are not essential for flight, such as the stomach and liver, while those that are essential for movement increase in volume. However, the presence of antibiotics in the bays, the places where the curlew and other species find their food, could alter its ability to complete all these adaptations in time to migrate.
In this context, experts in marine biology and ecology considered the need to measure which of these compounds are present in the environment and organism of this species, work led by Juan Navedo, head of the Bird Ecology Lab of the Institute of Marine and Limnological Sciences, and director of the Quempillén Experimental Station of the Faculty of Sciences of the Universidad Austral in Chiloé, under the auspices of the FONDECYT 1161224 project, "Assessing sub-lethal pollution effects on wildlife: prevalence of antibiotic resistance in coastal environments and associated costs to migratory birds".
In this study, developed jointly with Claudio Verdugo, researcher at the Faculty of Veterinary Sciences of the Austral University, and Valeria Araya, PhD student in Marine Biology at the same institution, we specifically investigated the presence of resistant bacteria and resistance genes to different antibiotics in the sediments of coastal wetlands and in the intestinal microbiota of curlew birds. For this purpose, two bays in Chiloé were investigated: the first, to the north in the Chacao channel, 30 km from the nearest marine farming center; and the second, near the Dalcahue channel, surrounded by marine farming centers.
The first results of this research were published in 2021 in the prestigious journal Science of the Total Environment under the title (translated) "Lifting a silent pollution: antibiotic resistance in coastal environments and transfer to long-distance migratory shorebirds".
Antibiotic footprint
As is well known, the marine phase of salmon farming is carried out in cages with high densities of fish, where the salmon are fed until they reach the desired size. There, together with the feed, they are given medicines for the treatment of different diseases, some of them of bacterial origin, such as Piscirickettsia salmonis.
"Seven antibiotics from different families were studied, three of them used exclusively in the salmon industry," explained Navedo, an academic with a PhD in Marine Biology and a PhD in Ecology and Evolution from the Faculty of Sciences at the Universidad Austral de Chile (UACh). The results obtained showed that 62% of the sediment samples, considering both bays, had resistant bacteria and resistance genes to at least one antibiotic, while only the area closest to the farming centers had multi-resistant bacteria.
In addition, 87% of the samples from the birds' cloacas showed bacteria resistant to at least one antibiotic, 63% being multiresistant, and some of them with a high pathogenicity potential. Finally, with respect to resistance genes, these were present in 46% of the bird samples, being multiresistant in many cases.
Visibility
The data from this study have been a concrete contribution to the visibility of the effects of these drugs on the environment and have been widely shared with the scientific community, for example, through the letter recently published in the journal Science (translated), "Salmon aquaculture threatens Patagonia".
In it, Navedo, together with Luis Vargas-Chacoff -also an academic of the Doctorate in Marine Biology of the U. Austral de Chile-, make a direct call to the Chilean Government to increase regulations for this industry, while at the international level they suggest pressuring to improve environmental policies in our country and thus stop the expansion of salmon farming.
Currently, together with other researchers and PhD students from the Bird Ecology Lab, Navedo is finishing the assembly of several experiments already carried out, in order to find out whether environmental exposure to antibiotics (non-clinical doses) has effects on any vital biological process in curlews, which would have implications for other vertebrates, including humans.
"In an experimental and environmental approach, we are observing how these components may have modified the composition of intestinal microbiota in vertebrates, since an imbalance in this bacterial community could cause dysfunctions in vital processes, such as, for example, the absorption of nutrients or the immune capacity," he explained.
Loading of waste
Although the conclusions of these experiments have not yet been published, the researcher emphasizes that it is essential to make transparent the load of antibiotic residues that passes from the culture cages to nature, considering that, according to the 2020 Report on the use of antimicrobials in national salmon farming of the National Fisheries and Aquaculture Service (Sernapesca), last year a total of 379 tons of antibiotics were used, reaching an annual harvest of one million 75 tons of salmon.
"To produce a kilo of salmon in Chile, 100 times more antibiotics are used than in Norway, which is the world's leading producer of this product. This volume of drugs reinforces the idea that the antibiotic footprint must be widely spread in the coasts of southern Chile and can even reach North America, through migratory birds, affecting multiple components of biodiversity, including human beings", emphasized the academic.
Finally, he pointed out that it is increasingly urgent, in the global context of 'One Health', to reduce salmon farming densities and to plan the capacity of cages that can be present in each area, as this will allow to limit the potential incidence of diseases and the volume of antibiotics used in the industry.