Their study was published in Environmental Science and Technology.
The researchers said some of the genes found could potentially confer resistance to common antibiotics and those of last resort, such as vancomycin.
The authors analyzed high-throughput ARG profiles in representative fishmeal products and the impact of fishmeal on the sediment resistome.
“A total of 132 unique ARGs and four mobile genetic elements (MGEs) were detected in five fishmeal products.”
“Up to 95 unique ARGs were found in fishmeal from China, while only 8 ARGs were present in fishmeal from Russia, suggesting ARG occurrence varied among fishmeal samples," they said.
The Chinese team traced back the abundant ARGs in fishmeal products to raw materials.
“Although thermal treatment (115 to 145 °C) during fishmeal processing kills most microorganisms in raw materials, ARGs may still persist as eDNA even after host bacteria have died. DNase treatment in this study indicated ARGs in fishmeal were present at higher concentrations as eDNA than as iDNA.”
No previous study had measured the broad spectrum of antibiotic resistance genes in fishmeal, said the authors, who are based at the Dalian University of Technology, China.
As millions of tons of fishmeal are used every year in formulated feeds for mariculture production, Jing Wang and colleagues said they wanted to see what its impact could be on the mariculture ‘resistome’ – the collection of resistance genes.
They argue that understanding the dynamics of ARG propagation and identifying their environmental reservoirs are critical for developing strategies to mitigate their spread.
“Antibiotic resistance genes (ARGs) are globally prevalent in mariculture sediment, and their presence is an issue of concern in the context of antibiotic use. Although large amounts of fishmeal have been released into the sediment, the role of fishmeal in ARG dissemination remains unclear.
“Our study has revealed for the first time that fishmeal itself is a major reservoir for ARGs, and the shift in the bacterial community induced by the nutrients in fishmeal is the main driver shaping the resistome in mariculture microcosm sediment. Our findings caution against the previously unperceived risk of ARG propagation in fishmeal-receiving ecosystems.”
Mariculture sediment is a hot spot for the global exchange of ARGs, explained the team.
ARGs in mariculture sediment enter the food chain via contaminated seafood and are at a high risk for transfer to human pathogens, they added.
“To date, most studies investigating antibiotic resistance and aquaculture have focused on the selective pressure exerted by the use of prophylactic and therapeutic antibiotics. However, there is growing awareness that abundant ARGs and [antibiotic resistant bacteria] ARB persist in mariculture sediment in the absence of antibiotics.”
They said tetracycline (TC), sulfonamide (SA), and trimethoprim (TMP) resistance genes are highly persistent in fish farm sediment in the Baltic Sea, even after several years without antibiotic usage. Antibiotic-resistant enterococci were also recovered from the sediment of a Mediterranean coastal fish farm despite the absence of selective pressure, while TMP resistance genes were screened in sediment bacteria isolated from a fish farm in Pakistan with no known history of antibiotic application, noted the authors.
Food safety inspections
The researchers said their findings highlight the importance of ARG detection in fishmeal during food safety inspections.
“In addition to mariculture production, fishmeal is also widely used in livestock, inland aquaculture, or organic fertilizer, and therefore the residual fishmeal in related ecosystems deserves more attention with respect to its impact on the bacteria resistome, even in the absence of prophylactic or therapeutic antibiotic use.
“As the growing collection of antibiotics is offset by ARGs, our results provided useful guidelines for animal feeding to control ARG dissemination. To mitigate ARG proliferation, appropriate feeding strategies or efficient microbial agents should be designed to eliminate residual fishmeal in the environment. We also recommend the development of improved technologies to remove eDNA in fishmeal during manufacturing.”
Source: Environmental Science and Technology
Title: Fishmeal Application Induces Antibiotic Resistance Gene Propagation in Mariculture Sediment
Authors: Y. Han, J. Wang, Z. Zhao, J. Chen, H. Lu, G. Liu