Histopathological analysis of filament formation of Nocardia farcinica in a silkworm infection model.

The silkworm Nocardia infection model has been established as a useful animal model for screening the pathogenicity of Nocardia and evaluating the therapeutic effects of antimicrobial agents against Nocardia infection. No histopathological analysis of silkworms infected with Nocardia farcinica has yet been performed. In this study, we performed histological analyses on organs of silkworms infected with N. farcinica. One day after infection with N. farcinica, the organism developed a branching filamentous form from coccid cells in the hemolymph. In addition, we evaluated effective doses (ED ₅₀ ) values by treating infected silkworms with amikacin 30 seconds and 24 hours after infection and found that the ED ₅₀ values treated within 30 seconds and 24 hours after infection were 4.1 μg/larva and 5.6 μg/larva, respectively. Evaluation of treatment with amikacin against the infected silkworms was unaffected by the growth process form of Nocardia. These results suggest that the silkworm Nocardia infection model is a useful tool for evaluating the antimicrobial therapy in the growth process of the N. farcinica.