The present study investigated the physiological and genetical effects of Gram negative bacteria (G^–) Escherichia coli and entomopathogenic Gram positive bacteria (G⁺) bacteria Bacillus thuringeinsis on the mulberry silkworm Bombyx mori (Lepidoptera: Bombycidae) were studied. The author used bioassays and molecular markers linked to 5^th instar larvae to bacterial injection to analyze the response of Bombyx mori. Also, the effect of both bacteria on the total and differential haemocytes count of the 5^th instar larvae of B. mori was evaluated. Results revealed that injection with E. coli increased the total haemocytes counts (THCs) about 59.09% up to control at 24 h post-infection. In this respect, B. thuringeinsis decreased the THCs by about 45.9, 58.39 and 69.4 % , respectively less than control after 48 hrs post-infection at concentrations of 50, 100, 150 µg/ml. Injection with E.coli increased the number of Pr, Pl and Gr and Oe. On contrast, injection with B. thuringeinsis significantly decreased the number of Pr, Pl and Gr and Oe. The mutagenic effect of the bacterial injection produced and/or affected several proteins that enable it to kill or causing larval deformation through the alteration on the physiological and genetic processes.