Pathogenic microbiomes on jellyfish reveal health risks beyond envenomation.

Jellyfish stings pose a growing public health concern in coastal regions, yet secondary bacterial infections arising from venom-induced tissue damage remain largely unexplored. Here we used shotgun metagenomics to characterize the surface microbiomes of Rhopilema esculentum, Chrysaora quinquecirrha and Stomolophus meleagris, profiling bacterial composition, virulence factors, antibiotic resistance genes and mobile genetic elements. We observed distinct host-specific microbiome signatures, with R. esculentum harboring the highest abundance of virulence-associated genes and notable enrichment of WHO priority pathogens including Staphylococcus aureus and Acinetobacter baumannii. Resistance genes conferring tetracycline, glycopeptide and fluoroquinolone resistance were prevalent across all species. Transposases comprised over 45% of mobile genetic elements, indicating substantial horizontal gene transfer potential. Validation using newly developed TaqMan qPCR assays across eight jellyfish species including the three aforementioned and five additional species, confirming that all harbored at least one opportunistic pathogen. These findings establish jellyfish surfaces as underappreciated reservoirs of antibiotic-resistant pathogens and highlight a potential, but as yet unproven, route of pathogen exposure following envenomation.