Salmon Aquaculture and Antimicrobial Resistance in the Marine Environment

Abstract

Antimicrobials used in salmon aquaculture pass into the marine environment. This could have negative impacts on marine environmental biodiversity, and on terrestrial animal and human health as a result of selection for bacteria containing antimicrobial resistance genes. We therefore measured the numbers of culturable bacteria and antimicrobial-resistant bacteria in marine sediments in the Calbuco Archipelago, Chile, over 12-month period at a salmon aquaculture site approximately 20 m from a salmon farm and at a control site 8 km distant without observable aquaculture activities. Three antimicrobials extensively used in Chilean salmon aquaculture (oxytetracycline, oxolinic acid, and florfenicol) were studied. Although none of these antimicrobials was detected in sediments from either site, traces of flumequine, a fluoroquinolone antimicrobial also widely used in Chile, were present in sediments from both sites during this period. There were significant increases in bacterial numbers and antimicrobial-resistant fractions to oxytetracycline, oxolinic acid, and florfenicol in sediments from the aquaculture site compared to those from the control site. Interestingly, there were similar numbers of presumably plasmid-mediated resistance genes for oxytetracycline, oxolinic acid and florfenicol in unselected marine bacteria isolated from both aquaculture and control sites. These preliminary findings in one location may suggest that the current use of large amounts of antimicrobials in Chilean aquaculture has the potential to select for antimicrobial-resistant bacteria in marine sediments.

The Ocean as a Global Reservoir of Antibiotic Resistance Genes

“…However, this greatly expands our knowledge of the diversity of genes responsible for these resistance patterns by linking resistance phenotypes to genotypes and identifying potential novel resistance genes. While the estimated frequencies of resistance we found (up to 0.9% of cells) are less than estimated in gulls (up to 5% resistant cells) (9) and aquaculture sediments (up to 15% resistant cells) (25), this study highlights the sheer abundance and diversity of potential AR genes across marine sites.…”

“…Because nitrofurantoin and sulfadimethoxine are synthetic antibiotics, microbes would not experience these molecules in natural microbe-microbe interactions. Resistant bacteria have been isolated from marine environments in proximity to aquaculture facilities or waterways in proximity to human influence (23,(25)(26)(27). In addition, Port and colleagues (24) showed that frequencies of known antibiotic resistance genes were higher nearshore, so anthropogenic inputs can influence resistance patterns.…”

Integrons: Past, Present, and Future

“…Like resistance genes, antibiotics are difficult to remove during water treatment, and some have long half-lives in the environment (219,220), resulting in pollution of both rivers and the ocean (221,222). The use of antibiotics in aquaculture adds these compounds directly into water bodies (223,224), raising local antibiotic concentrations. The environmental and health consequences of contaminating water bodies with antibiotics are of significant concern (225)(226)(227), with calls to monitor and control antibiotic pollution (121,228).…”

Influence of Maternal and Larval Immunisation against <i>Lactococcus garviae</i> Infection in Rainbow Trout <i>Oncorhynchus mykiss</i> (Walaum) Lysozyme Activity and IgM Level

“…The aquaculture industry is recently facing a serious setback due to infectious [23] diseases leading to severe economic loss [24]. Although mortalities have been reported in all stages of life, maximum mortalities in all the cultivated fish species have been reported at larval stages.…”