Salmon industry in Chile and increased bacterial resistance to antibiotics: Shorebirds are reservoirs and potential spreaders

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  • Scientists recorded multi-resistant bacteria and antibiotic resistance genes in the migratory water bird “straight-billed curlew”, which lives in Chiloé where the salmon industry operates, and which migrates to the northern hemisphere in a journey of thousands of kilometers.
  • Antibiotics used intensively in Chilean salmon farming increase the appearance of multi-resistant bacteria, with migratory shorebirds being reservoirs and potential diffusers of multi-resistant bacteria and genes.
  • Scientists demand limiting the use of antibiotics in protected areas under the “One Health” approach promoted by the World Health Organization (WHO).



Ancud, June 18, 2021. (Ecoceanos News) – Researchers from the Austral University of Chile published a study in which they describe how marine salmon farms, widely deployed in the Chiloé archipelago, are influencing the dispersal of multi-bacterial bacteria. -Antimicrobial resistant (ARB) and antibiotic resistance gene (ARG). The surprising thing is that these resistances would be being transferred from Chiloé beaches hundreds of thousands of kilometers by at least one shorebird.

To do so, they evaluated the presence of ARB and ARG in the migratory aquatic bird “straight-billed curlew” (Limosa haemastica), to study the antibiotic footprint in wildlife associated with human activity.

Researchers Juan G. Navedo, Valeria Araya and Claudio Verdugo affirm that antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) are widespread in sediments and shorebirds in Chiloé. And they warn that migratory shorebirds are reservoirs and potential spreaders of this type of bacterial resistance.

The scientists took sediment and intestinal microbiota samples from these birds in Pullao Bay, -which is part of a large area of ​​intensive salmon farming activity without the presence of a large human population-, and in Caulin Bay, where a small community of people lives, and a health center, where the closest salmon farms were 20 km away.


Read the study «Upraising a silent pollution: Antibiotic resistance at coastal environments and transference to long-distance migratory shorebirds», here.


Multiresistant phenotypes to five antibiotics used in Salmon Industry

The experts did not find significant differences regarding the occurrence of ARB and ARG in both bays, nor in sediment samples, nor in samples of the microbiota of seabirds, a fact that they attributed to the low number of samples used.

However, they found multi-resistant ARB in sediments from the bay surrounding the aquaculture operations (Pullao), as well as a higher occurrence of ARB and ARG.

All bacteria were susceptible to florfenicol and two isolates showed resistance to OXT (oxytetracycline) in Pullao. Other isolates showed resistance to ENR (enrrofloxacin), CFP (cefoperazone), CXM (cefuroxime) and CN (gentamicin).

“Our results also reinforce previous ARG findings (against antibiotics used in salmon farming) in sediments far from aquaculture areas, highlighting that the antibiotic footprint can extend beyond the geographic influence of antibiotic sources and transfer to wildlife ”, say UACh scientists.

According to Sernapesca, during 2020, florfenicol (98%), oxytetracycline (0.8%), tiamulin (0.5%) and tilmicosin (0.02%) were used in the seawater phase of industrial salmon farming.

Seabirds have multi-resistant and potentially pathogenic bacteria

Regarding the samples collected from birds, 87% showed at least one bacteria multi-resistant to antimicrobials, 63% being multi-resistant and some of them with a high potential pathogenicity, however the frequency of the multi-resistant phenotypic was comparatively more high in Caulin birds.

The most common combination of multi-resistant phenotypes in birds was against erythromycin, cefurozime, and florfenicol in Caulin Bay, while erythromycin and cefuroxime were in Pullao Bay.

Chiloe: Consequences of 20 years of abusive use of antibiotics in salmon farming

Faced with this fact, the scientists pointed out that it is very likely that these results have been due to “antibiotic residues transferred by the relevant current speed associated with the tidal cycles in the Chacao channel after more than twenty years of treatment with antibiotics in the Reloncaví estuary, with the most common association that includes resistance to two of the three most used antibiotics in Chilean aquaculture”.

The researchers conclude that “our results reinforce the idea that the antibiotic footprint can extend globally and beyond the geographic influence of antibiotic sources, especially in coastal environments where migratory birds act as reservoirs and as potential propagators of resistance to antibiotics ”.

It is imperative and urgent to limit the use of antibiotics in the industrial production of salmon

The recognition of the main sources of antibiotics in each area is necessary to limit their inappropriate and massive use, which would also serve both for the conservation of mobile species (such as shorebirds) and as a measure for human well-being under a ‘ One health ‘recommended by the WHO, say the authors

According to WHO “The concept of “ one health ”summarizes an idea that has been known for more than a century: that human health and animal health are interdependent and are linked to the health of the ecosystems in which they exist. We envision and implement it as a collaborative global approach to understanding risks to human and animal health and the health of the ecosystem as a whole.


RESUME:

• Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) are widespread in sediments and shorebirds in Chiloé.
• Antibiotics used in salmon aquaculture increase the appearance of multi-resistant ARB.
• Migratory shorebirds are reservoirs and potential spreaders of ARB and ARG.
• The antibiotic fingerprint is clearly detected even in an area sparsely populated by humans.
• Limiting the supply of antibiotics to protected areas seems urgent under the One Health approach.


Read the study «Upraising a silent pollution: Antibiotic resistance at coastal environments and transference to long-distance migratory shorebirds», here.