In our present study, the immunological efficiency of brown Mel1 extracted from Streptomyces longisporoflavus NR043926 and black Mel2 extracted from Aspergillus niger MT355517 on bacterial pathogenicity was investigated. Mel1 and Mel2 were extracted and purified from the dried microbial biomass. Chemical characterization of extracted MeI pigments were compared with standard melanin. In vivo, estimation of the protective action of these pigments against Escherichia coli infection in Swiss albino mice which was identified by molecular characterizations 16S rRNA gene sequences, Albumin content was reduced in +ve control group (infected non – treated mice), while liver enzymes (ALT & AST) were increased in comparison to normal values were detected in immunized mice with Mel pigments. Eosinophil, monocyte values showed a non-difference, while the changes in lymphocyte numbers were paralleled to the response of total leukocyte counts. Serum antibodies total IgM in the non-immunized (+ve control group) mice were markedly lower than those observed in immunized mice (prevention groups and treated groups) with microbial melanin which can stimulate immunity system. Mel2 had high immunoprotection defense against E. coli infection in comparison to Mel1.