Identification and toxicity evaluation of a Klebsiella pneumoniae strain isolated from diseased Eri silkworm (Samia ricini) with relevance to sericulture practices

The eri silkworm ( Samia ricini ) is an economically important non-mulberry silkworm extensively cultivated in Northeast India for its unique spun silk. Disease outbreaks among larvae, often of gut origin, pose a significant threat to sericulture in this tropical region. In the present study, a bacterial isolate (S1_4) was recovered from the gut of diseased S. ricini larvae and identified as Klebsiella pneumoniae through 16S rRNA gene sequencing and phylogenetic analysis. Pathogenicity was assessed via toxicity bioassays, revealing a time-dependent increase in mortality. LC₅₀ values were determined to be 8.45 × 10⁸, 2.20 × 10⁷, 7.58 × 10⁶, and 7.49 × 10⁴ CFU/ml at 24, 48, 72, and 96 hours post-infection, respectively. Infected larvae exhibited sepsis-like symptoms and progressive death. This is the first report implicating K. pneumoniae in the pathology of S. ricini , establishing a previously undocumented host–pathogen association. These findings highlight the importance of microbial surveillance and early disease detection in tropical sericulture and suggest that S. ricini may serve as a promising invertebrate model for studying bacterial virulence and host–pathogen interactions.