<i>Klebsiella pneumoniae</i> pathogenicity in silk moth larvae infection model

The emergence of antibiotic resistant bacteria is a major health concern worldwide in recent years. The objective of this study is to establish the larvae of the silk moth (commonly known as silkworm), Bombyx mori as an infection model to study antibacterial effect of antibiotics against Klebsiella pneumoniae. In this study, the pathogenicity of a K. pneumoniae strain isolated from food to silkworm larvae was examined. Within 72 h of bacterial injection, all silkworm larvae were killed in a dose-dependent manner with their body color turning into black due to increased melanization. Bacterial numbers in the larval hemolymph (blood) significantly increased after 9 h of infection with a decrease in viable circulatory hemocytes in hemolymph. When presented with bacteria laden leaves, larvae did not eat but injection of bacteria directly into the midgut killed larvae within 12 h with a higher load required in comparison to that required for the killing by hemolymph injection. Administration of four different antibiotics into larval hemolymph showed therapeutic effect at different doses with varying efficacies against hemolymph-injected K. pneumoniae. These results indicate that the silkworm larvae can be used as an infection model not only to study the pathogenicity of K. pneumoniae but also to perform rapid screening for the identification of antibiotics effective against multidrug-resistant strains of K. pneumoniae.