Silkworm (<i>Bombyx mori</i>) as a novel infection model for fish-derived <i>Aeromonas hydrophila</i>

Aeromonas hydrophila is a significant pathogenic bacterium in aquaculture and the ornamental fish industry, causing lethal infections in fish and contributing to rising drug resistance. This leads to substantial economic losses and underscores the urgent need for new treatments and infection controls. However, the lack of a simple, sensitive infection model has hindered studies on the pathogenicity of A. hydrophila and therapeutic evaluation. This study introduces the silkworm (Bombyx mori) as a highly sensitive and cost-effective infection model for A. hydrophila. Using a strain isolated from diseased Wakins (goldfish), the pathogenicity of A. hydrophila was confirmed in silkworms, which exhibited a much lower median lethal dose (LD₅₀ = 0.3 CFU/larva) compared to Wakins (LD₅₀ = 5.1 × 10⁶ CFU/g body weight). This demonstrates the silkworm's higher sensitivity to A. hydrophila. The in vivo efficacy of three antibiotics (gentamicin, kanamycin, and tetracycline) was also tested. Gentamicin and kanamycin prolonged survival in both models, while tetracycline also showed efficacy in both models, though its effect was weaker in the silkworm model. This highlights the silkworm model's utility in evaluating bactericidal agents against A. hydrophila. This model addresses key limitations of traditional fish infection models, including low sensitivity, long experimental durations, and high costs. The silkworm-based method enables efficient investigation of A. hydrophila pathogenicity and rapid screening of potential treatments, accelerating the development of new therapeutic strategies for aquaculture and beyond.