Silkworm as an animal infection model for the screening of environmental, clinical and veterinary pathogens

Silkworm, Bombyx mori, has passive immunity and can be infected by pathogenic bacteria. Therefore, it can be used as a robust bacterial infection model for screening of pathogenic isolates from various sources. In this work, 11 environmental, clinical and veterinary isolates were screened for pathogenicity using silkworm larvae by injecting bacterial suspension through their dorsal surface and observing response. Experimental conditions were established by using Bacillus thuringiensis SW_R_F_1, Escherichia coli 0157:H7, E. coli DH5a and 0.6% saline. Nine out of 11 isolates were detected pathogenic after screening. The biochemical and genomic analysis of the nine test isolates confirmed their pathogenicity. The LD₅₀ of Pseudomonas aeruginosa 47D and Salmonella Typhimurium 77 were 4.63x107 at 12 hours was 8.02x10⁷ cells/lOOμI/gram at 24 hours respectively. These results indicated that silkworm exhibits differential pathological response for pathogenic and nonpathogenic bacteria, and can be used as an alternative to animal model for screening diverse isolates.