A metagenomics-based approach to decipher the resistome and mobilome of two seahorse species, Hippocampus barbouri and Hippocampus comes.

Objective: This study aimed to explore the abundance and diversity of antibiotic resistance genes (ARGs) in seahorses (Hippocampus barbouri and Hippocampus comes) and their surrounding environment.
Methods: A combination of shotgun metagenomics and bioinformatics was used to investigate the resistome of both seahorse species.
Results: The analyses demonstrated a higher abundance of ARGs in seahorse-associated microbiomes, particularly in skin and gut samples, compared to those from water and sediment. Interestingly, genes conferring multidrug resistance (e.g., acrB, acrF, cpxA, msbA, and oqxB) were highly prevalent in all samples, especially in skin and gut samples. High levels of genes conferring resistance to fluoroquinolones (e.g., mfd and emrB), β-lactam (e.g., bla _CMY-71 , bla _OXA-55 , and penA), aminocoumarin (e.g., mdtB and mdtC), and peptide antibiotics (arnA, pmrE, and rosA) were also observed in skin and gut samples. An enrichment of mobile genetic elements (MGEs) was also observed in the analysed samples, highlighting their potential role in facilitating the acquisition and spread of ARGs. In fact, the abundance of mobilisation (MOB) relaxases (e.g., MOBF, MOBP, MOBT, and MOBV) in gut and skin samples suggests a high potential for conjugation events.
Conclusions: The occurrence of ARGs and MGEs in seahorses and the surrounding environment raises concerns about their transmission to humans, either through direct contact or the consumption of contaminated seafood. To the best of our knowledge, this study represents the first comprehensive analysis of ARGs in seahorse-associated microbiomes, and its results emphasise the need for monitoring and controlling the spread of ARGs in environmental settings.
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