Rapid biosynthesis of silver nanoparticles from Bacillus megaterium (NCIM 2326) and their antibacterial activity on multi drug resistant clinical pathogens
Graphical abstract
Highlights
► Rapid biosynthesis of Ag-BNPs from the cell free extract of B. megaterium (NCIM 2326). ► Characterization of Ag-BNPs by UV-vis spectroscopy, TLC, AFM and FTIR spectroscopy. ► The study confirms Ag-BNPs to have efficient antimicrobial properties against MDR clinical pathogens, S. pneumoniae and S. typhi.
Introduction
Nanotechnology is the emerging field in 21st century which is the root cause for next industrial revolution. Synthesis, characterization, manipulation and application of nanomaterials are being rapid development in nanotechnology. Nanoparticles are the building blocks of nanotechnology as they play major role in their applications. The application of nanoscale materials and structures may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine and water treatment [1], [2].
Metal nanoparticles are of much importance due to their high specific surface area and a high fraction of surface atoms, have been studied in great extent because of their unique physiochemical characterization which includes catalytic activity, optical properties, electronic properties, antimicrobial activity, magnetic property [3], [4] and biomedicine [5], [6], [7], [8]. The exploring bactericidal effect of metal nanoparticles is the leading research field in this decade, but it was also accepted that nanoparticles may have detrimental effects in the ecosystem [9], [10]. Among metal nanoparticles (cadmium sulfide, gold and silver) [11], silver nanoparticles (Ag-NPs) have effective antimicrobial activity [12], [13], [14], [15], [16], especially bactericidal effect [17], [18], [19], [20], [21]. In this modern world the pathogens are resistant to multiple antimicrobial agents [22] is being a major problem, e.g. Staphylococcus aureus resistant to Methicillin and Candida albicans resistant to Fluconazole [23] and many pathogenic bacteria [24], [25].
Silver nanoparticles can be produced by physical and chemical methods [26], [38] they can also be produced in biological methods specifically by bio-reduction [27], [28], [29]. As the physical and chemical method uses toxic chemicals in their synthesis, it raises great concern for environmental reasons [30], now it became immense research study for the production of Metal Nanoparticles (MeNPs) in safe, reliable, clean, ecofriendly way. So the biosynthesis of the MeNPs from microorganisms and plants is being developed. The synthesis and assembly of NPs from of clean nontoxic and environmentally acceptable ‘Green chemistry’ procedures involves microorganisms and plants [31]. Both unicellular and multicellular organisms are known to produce inorganic materials either intracellularly or extracellularly [32], [33], [34], [35]. Biological production systems are of special interest due to their effectiveness and flexibility.
The bactericidal effect of silver nanoparticles is due to their small size and high surface area to volume ratio, which allows them to interact closely with microbial membranes [36]. Smaller particles with a larger surface area have effective antibacterial activity [37] and it is also known that bactericidal effect of silver nanoparticles decreases as the size increases and is also affected by the shape [38]. Effect of the shape on the antibacterial activity of has recently been reported [39].
Several studies propose Ag-NPs may attach to the surface of the cell membrane disturbing and altering the functions of the cell [40]. The damage of the cell may be caused by interaction of Ag-NPs with phosphorous and sulfur-containing compounds such as DNA and proteins. Silver tends to have a high affinity for such compounds [41], [42]. Silver ions strongly interact with the available –SH groups of the biomolecules to inactivate the bacteria [43]. Furthermore, the antibacterial activity of silver ion under anaerobic conditions was found less potent than in oxygen rich environment [44]. Such interactions in the cell membrane would prevent DNA replications [45] which would lead to bacterial death [46], [47].
The present investigation has focused on extracellular biosynthesis of highly stable silver bionanoparticles (Ag-BNPs) and to determine the antibacterial efficacy against multi drug resistant clinical bacterial pathogen. These stable Ag-BNPs were be synthesized by using a bacterium Bacillus megaterium (NCIM 2326) to access their antimicrobial activity against Multi Drug Resistant (MDR) clinical pathogens such as Streptococcus pneumoniae and Salmonella typhi. The study also includes the characterizations of Ag-BNPs by UV–vis spectrophotometer, TLC, Atomic Force Microscopy (AFM) and FTIR spectral analysis. Based on the problem of emerging antibiotic resistant strains, the present work would be a major research effort to discover alternative strategies (Nanomedicine) for the treatment of multi drug resistant bacterial infections.
Section snippets
Media and chemicals
All the media components and analytical reagents were purchased from Hi-Media Laboratories Pvt Ltd. (Mumbai, India) and Sigma Aldrich Chemicals (St. Louis, USA).
Microorganisms
The bacterial strain B. megaterium (NCIM 2326) obtained from NCL, Pune and the multi drug resistant Bacterial pathogenic strains obtained from SRM medical college hospital and research centre, Kattankulathur, Chennai. The strains were maintained on nutrient agar medium at 37 °C and preserved at 4 °C for further study. These strains were
Result and discussion
Nanotechnology is fast emerging discipline in the field of life science. Biologists are highly interested in synthesizing bionanoparticles using many of the precious metals. A comprehensive study of extracellular biosynthesis of Ag-BNPs was carried out in this research work. The pure culture (Fig. 1.) of B. megaterium (NCIM 2326) was inoculated and incubated in Muller Hinton broth and the cell filtrate obtained was subjected to 1 mM AgNO3. The reaction was started within few minutes of
Conclusion
The present study demonstrated the use of B. megaterium for the potential extracellular synthesis of Ag-BNPs in the range of 80–98.56 nm. The rapid synthesis of nanoparticles would be suitable for developing large scale productions and the extracellular synthesis would make the process simpler and easier for downstream processing. The present research work showed that the synthesized nanostructure by this process is ready for the application in the field of Nanomedicine against multidrug
Acknowledgements
The authors gratefully acknowledge to management, SRM University, Kattankulathur, Chennai, India for providing all the laboratory facilities and funding. We would like to acknowledge Nanotechnology research centre & School of Pharmacy, SRM University for AFM & UV–vis Spectrophotometer analysis. The authors are also grateful to SAIF (Sophisticated Analytical Instrumental Facility)-IITM, Chennai, India for FTIR analysis.
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