Summary In the present scenario, pharmaceutical and biomedical sectors are facing the challenges of continuous increase in the multidrug‐resistant (MDR) human pathogenic microbes. Re‐emergence of MDR microbes is facilitated by drug and/or antibiotic resistance, which is acquired way of microbes for their survival and multiplication in uncomfortable environments. MDR bacterial infections lead to significant increase in mortality, morbidity and cost of prolonged treatments. Therefore, development, modification or searching the antimicrobial compounds having bactericidal potential against MDR bacteria is a priority area of research. Silver in the form of various compounds and bhasmas have been used in Ayurveda to treat several bacterial infections since time immemorial. As several pathogenic bacteria are developing antibiotic resistance, silver nanoparticles are the new hope to treat them. This review discusses the bactericidal potential of silver nanoparticles against the MDR bacteria. This multiactional nanoweapon can be used for the treatment and prevention of drug‐resistant microbes.

Re-emergence of resistance in different pathogens including viruses are the major cause of human disease and death, which is posing a serious challenge to the medical, pharmaceutical and biotechnological sectors. Though many efforts have been made to develop drug and vaccines against re-emerging viruses, researchers are continuously engaged in the development of novel, cheap and broad-spectrum antiviral agents, not only to fight against viruses but also to act as a protective shield against pathogens attack. Current advancement in nanotechnology provides a novel platform for the development of potential and effective agents by modifying the materials at nanolevel with remarkable physicochemical properties, high surface area to volume ratio and increased reactivity. Among metal nanoparticles, silver nanoparticles have strong antibacterial, antifungal and antiviral potential to boost the host immunity against pathogen attack. Nevertheless, the interaction of silver nanoparticles with viruses is a largely unexplored field. The present review discusses antiviral activity of the metal nanoparticles, especially the mechanism of action of silver nanoparticles, against different viruses such HSV, HIV, HBV, MPV, RSV, etc. It is also focused on how silver nanoparticles can be used in therapeutics by considering their cytotoxic level, to avoid human and environmental risks.

We report the extracellular synthesis of silver nanoparticles using an endophytic fungus Pestalotia sp. isolated from leaves of Syzygium cumini (L) and their antibacterial activity against human pathogenic bacteria viz. Staphylococcus aureus (ATCC-25923) and Salmonella typhi (ATCC-51812) alone and in combination with commercially available antibiotics. Detection of synthesized silver nanoparticles was carried out using UV-Visible spectrophotometer analysis, which showed a peak at 415 nm indicating the formation of nanoparticles. Further characterization includes the Fourier Transform Infra-Red spectroscopic analysis for the detection of proteins as capping agents on nanoparticles. Nanoparticle Tracking and analysis (LM 20) and TEM analysis confirmed the formation of spherical and polydispersed nanoparticles in the range of 10-40 nm having average size of 12.40 nm. Biologically synthesized silver nanoparticles showed significant antibacterial activity but their efficacy was increased in combination of antibiotics like gentamycin and sulphamethizole. Silver nanoparticles in combination with gentamycin showed maximum activity (30 mm) against S. aureus followed by sulphamethizole (25 mm). Similar results were reported in case of S. typhi where silver nanoparticles in combination with gentamycin (28 mm) showed more activity than combination of silver nanoparticles and sulphamethizole (24 mm). Biosynthetic approach using an endophytic fungus is a novel way towards the development of safe, economically viable and green method for the synthesis of silver nanoparticles and thus synthesized silver nanoparticles can be used in antibacterial formulations.

The present study reports the synthesis of silver nanoparticles (AgNPs) using both biological and chemical routes to find out the best method for control of their size and activity. The fungal agent (Fusarium oxysporum) and the plant (Azadirachta indica) were found to be the best source for AgNPs synthesis. Both biosynthesis and chemosynthesis were achieved by challenging filtrate with AgNO3 (1 mM) solution. The synthesised nanoparticles were characterised by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, nanoparticle tracking analysis (LM20), zeta potential measurement and transmission electron microscopy. The biologically synthesised nanoparticles were spherical, polydispersed and in the range of 10-40 nm, while chemically synthesised nanoparticles were highly monodispersed with a size of 5 nm. The antimicrobial assay against Escherichia coli and Staphylococcus aureus proved biogenic AgNPs to be more potent antibacterial agents than chemically synthesised AgNPs. The possible antibacterial mechanism of AgNPs has also been discussed. Biogenic AgNPs have shown more activity because of the protein capping and their mode of entry into the bacterial cell. These findings may encourage the use of biosynthesis over the chemosynthesis method.

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