Changes in bacterial community composition and antibiotic resistance profiles of coral-associated microbiota in the vicinity of Chilean salmon farms

Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine

The extensive use of antibiotics in Chilean salmon farming raises concerns about harmful effects on benthic habitats, particularly the iconic cold-water coral (CWC) banks in semi-enclosed fjords. We collected specimens of the CWCnear and far from salmon farms in Comau Fjord, Chile, and investigated their associated bacterial community (metabarcoding, culturing) and screened bacterial isolates for their antibiotic resistance (15 antibiotics, including antibiotics common in Chilean salmon farming). The cultured bacterial isolates ofshowed a slight but significant increase in antibiotic resistance (near: 7.7 ± 0.47 vs. far: 6.3 ± 0.48). This was accompanied by a change in dominance in the randomly selected isolates, withanddominating far and near, respectively. Metabarcoding also showed a shift in the dominant bacterial strains from SUP05 clade toand a loss ofstrains near the salmon farm. Common antibiotics used in salmon farming, however, significantly reduced bacterial growth at the community level, and most bacterial isolates were also sensitive to these antibiotics, except for tilmicosin. This may provide a first indication of how salmon farms modify the microbiome ofand underscores the need to expand such assessments in space and time. Supplementary Information The online version contains supplementary material available at 10.1038/s41598-026-57517-y. Abs1