Identification and Pathogenicity of Enterobacter Cloacae Isolated from Diseased Eri Silkworm Samia Ricini

The eri silkworm (Samia ricini) is a vital non-mulberry silk producer in North East India, yet its production is frequently threatened by microbial diseases. In the present study, bacteria were isolated from diseased larvae and screened for pathogenicity. One isolate, designated S2_11, formed creamy white, irregular-edged colonies and was identified as Enterobacter cloacae through 16S rRNA gene sequencing and phylogenetic analysis (GenBank accession PP506516; 99.2% similarity). Experimental infection of healthy fifth-instar larvae revealed dose- and time-dependent mortality, accompanied by typical septic symptoms. Probit analysis yielded median lethal concentration (LC₅₀) values of 9.86 x 10⁷, 1.24 x 10⁷, 4.45 x 10⁶, and 3.08 x 10³ CFU/ ml at 24, 48, 72, and 96 h post-injection, respectively. These findings establish E. cloacae as a pathogenic bacterium of S. ricini and highlight the importance of molecular surveillance in developing effective disease management strategies for sericulture.