Extra / intracellular biosynthesis of silver nanoparticles from potential bacterial species

Scientists have found that silver nanoparticles made using bacteria have better antibacterial properties than their chemically synthesized counterparts. Biological synthesis of these particles is really just an offshoot of a response mechanism of bacteria from metal stress. The present study showed the synthesis of the metallic nanoparticles from the bacterium which has natural antibacterial activity and their effectiveness on various pathogens. These bacteria were named as potential bacteria and selected for synthesis of silver nanoparticles. The bacteria were collected from different sources viz., soil and water. Ten potential bacteria named S1-S10 were selected for pure culture. Screened out bacteria were treated with silver nitrate (AgNO₃). Synthesis of silver bio-nanoparticles was done by intra- cellular method. The bacteria were treated under sonication and centrifugation. The pellets and cell filtrates were separated and treated separately with silver nitrate (AgNO₃). The silver nanoparticles formed were characterized by atomic force microscopy (AFM) and the optical density with spectra was taken through UV VIS-spectrometry. The silver nanoparticles after confirmation were checked for their antibacterial activity against Staphylococcus epidermidis, Bacillus cereus and E. coli and were compared with the raw extract of the potential bacteria and the normal bacteria. SI, S4 and S10 showed the antimicrobial activity to all the three pathogens, where as S10 showed the maximum zone of inhibition 14.7mm against E. coli and S8 against Bacillus cereus 14.3mm. The zone of inhibition was more in silver bio-nanoparticles than compared to the raw sample. The highest sensitive antimicrobial activities were observed in E. coli followed by Bacillus cereus and Staphylococcus.