Antibacterial activity of the streptomycetes isolated from marine soil sample

Streptomyces species are the source of 70% of known antibiotics and they live in the soil where they encounter antibiotics produced by competing microbes, including other actinomycetes. Antibacterial activity of streptomycetes isolated from muttukkad area in Tamil Nadu has been studied. A total of 50 streptomycetes were subjected to primary screening by cross streak method against Gram-positive (Staphylococcus aureus, S.epidermidis) and Gram-negative (Escherichia coli, Klebsiella species, Proteus species, Pseudomonas species) test bacteria. It was observed that 5 isolates were active against all bacteria. Altogether 5 putative isolates were subjected to secondary screening by agar well diffusion method to further test the capabilities of primarily screened organisms. Finally 1 isolates Streptomyces species were selected for further study on the basis of broad spectrum activity . The antibacterial substances were extracted with ethyl acetate from isolate-inoculated starch-casein broth fermented for 7 days at 28°C by solvent extraction method. The crude extract were subjected to secondary screening. Out of 5 isolates only one isolate showed more activity against all the microbial pathogens. The most potential isolate was identified as Streptomyces cacaoi SU2 (JF730119) based on its morphological, cultural, biochemical features and also confirmed by 16s rRNA partial gene sequencing.