Antibacterial Applications of Biosynthesized AgNPs: A Short Review (2015-2020)

Bacterial resistance to a wide spectrum of antimicrobial medicines has evolved as a major public health concern. Antibiotics are medications that are used to kill microorganisms that could cause serious illness or death. Nanotechnology has exploded as a significant and appealing field of research, with innovative features and functionalities in a variety of fields. Silver is a versatile antibacterial and anticancer medicinal agent in the form of nanoparticles. Silver Nanoparticles (AgNPs) have been implicated in a wide variety of medicinal benefits. This review article addresses antibacterial applications of biosynthesized AgNPs that have been researched over the last decade. AgNPs' antimicrobial potential against a variety of bacterial agents is discussed. CONTACT Kailas H. Kapadnis prof.kailaskapdnis@gmail.com Department of Chemistry, MGV’s LVH Arts, Science and Commerce College, Nashik, India (Affiliated to SP Pune University, Pune). © 2021 The Author(s). Published by Enviro Research Publishers. This is an Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC-BY). Doi: http://dx.doi.org/10.13005/msri/180203 Article History Received: 29 April 2021 Accepted: 29 June 2021


Introduction
Thinking about the commonness of different diseases, infections brought about by any type of microorganism ought not to be messed with; they can go through fundamental changes and cause serious medical problems. Antimicrobial resistance is quickly becoming one of the most severe medical problems of current day. [1][2][3] Even after significant advancements in antimicrobial therapy, infectious diseases triggered by microorganisms remain a major public health issue owing to the rise of susceptibility to currently accessible antibacterial medications. 4 Bacterial resistance to a wide variety of antimicrobial drugs is becoming a leading health concern. 5, 6 Antibiotics are substances that are used to destroy bacteria that can cause life-threatening conditions. 7,8 In light of these pressing concerns of modern time, it is critical to establish new antimicrobial agents that are more selective and reliable in their antimicrobial potential. 9,10 Numerous antimicrobial agents are targeted and developed in order to tackle the problem of antimicrobial resistance. [11][12][13] Organic chemists are targeting the synthesis of variety of potent heterocyclic compounds and are also successful in developing new antimicrobial agents. [14][15][16][17][18][19][20] However, research from last ten years has proved that the AgNPsare proved as potent antimicrobial agents. [21][22][23][24][25] From ancient times, it has been established that silver is a very good medicinal elements. From this perspective researchers have adopted many bio strategies based on plants to develop more powerful antibacterial AgNPs. 26,27 To their credit, AgNPs are synthesized by various green approaches with good efficacy in the antibacterial action. 29,29 Through use of silver as an anticancer and antibacterial agents has developed exponentially. 30,31 It has been proved that various plants contain organic compounds that are capable of producing AgNPs from silver salts. 32,33 Plant extracts such as stem, root, nuts, bark, and marine bio resources are among the numerous green resources used for the synthesis of AgNP's. The extracts obtained from plants are found to be the best alternative for the synthesis of AgNP's due to their easy accessibility, nontoxic quality, and inclusion of exceptional bioactive compounds with high therapeutic attributes. Plants are being used in the synthesis of AgNPs, and particles of various shapes and sizes have indeed been produced. Given the significance of the above reasons, this review article focuses on antibacterial applications of biosynthesized AgNPs that have been studied over the last decade. The antimicrobial ability of AgNPs against a wide spectrum of bacteria is addressed.

Biosynthesis and Antibacterial Properties of AgNPs
The therapeutic potential of AgNPs in treating diseases is promising in the realm of bio-Nano medicine. AgNPs are candidates for groundbreaking applications in the biomedical industry as antibacterial, antifungal, antioxidant, and anticancer agents due to their small stature, large surface area, and chemical characteristics, and these applications are well established. The traditional chemical methodswereused to generate nanoparticles, however, this methodologies are connected with dangerous materials that are unsafe.
Plant-mediated biosynthesis of nanoparticles, on the other hand, is growing rapidly owing to its low toxicity, resource efficiency, eco-friendliness, and quickness.Plants based natural sources include bioactive compounds such as flavonoids, proteins, polysaccharides, polyphenols, terpenoids, tannins, alkaloids, ketones, aldehydes, amines, etc., which function as reducing, bolstering, and capping agents in the transformation of metal ions to metal nanoparticles, resulting in the generation of desirable nanoparticles with preconfigured characteristics.Among the several biosynthesized metal nanoparticles, AgNPs were selected as the favourites in the realm of antibacterial applications. In the following sections, we'll go over some of the best instances from 2015 to 2020.

Year 2015
The selected examples (year 2015) of antibacterial applications of biosynthesize AgNPs is given in Table 1. Saravanakumar et al. 34 reported, the biosynthesis of AgNPs using Cassia tora leaf extract. This is an easy, cost-effective, fast, and environmentally friendly way to make AgNPs that can be accomplished in a short while. Furthermore, this process could be used at room temperature. This method yielded spherical AgNPs with well-defined characteristics which were uniformly polydispersed with face centered cubic geometry. Importantly, no capping agent was used in the AgNP synthesis. Gram positive (S. aureus, B.subtilis) and Gram negative (E. coli, P. aeruginosa) bacteria were tested for antibacterial activity. Gram negative bacteria were shown to have a larger inhibitory effect than Gram positive bacteria in their research. Miri et al. 35 used Prosopis fracta leaves extract to demonstrate a green, simple, and single-pot process for the biosynthesis of antibacterial AgNPs.This method is fast, reliable, and environmentally friendly, and it can be used to make all sorts of metal nanoparticles from a wide range of extracts. The obtained AgNPs had a spherical form, with a mean diameter of about 8.5-11 nm, according to spectral analysis. These findings show that organic biomolecules in Prosopisfracta extract showing reducing as well as capping nature. The antimicrobial action of Ag-NPs was tested against S.aureus, B.subtilis, and E.coli, P.aeruginosa. Antibacterial activity was comparable to that of the control group. According to Kokila et al. 36 AgNPs were produced via the direct interaction of silver nitrate with Cavendish banana peel extract in aqueous media, without the use of any external reagents. As a result, this reaction pathway satisfies all of the requirements for a completely environmentally friendly chemical process. The antibacterial effect of synthesized AgNPs displayed high antimicrobial activity against S.aureus, B. subtilis, K.pneumonia and E.coli. Psidiumguajava leaf extract P. aeruginosa 38 Manikandan et al. 37 made AgNPs (AgNPs) using Rosa indica petals' ethanol extract and tested them against human pathogenic bacteria. AgNPs were round in shape and spaced widely apart when they were produced. The size of AgNPs was determined as 23.52 and 60.83 nm. The defined AgNPs demonstrated a more effective antibacterial property.
The presented AgNPs showed a more compelling antibacterial effect against E. coli, K. pneumonia, S. mutans, E. faecalis. Bose et al. 38 reported a very quick, efficient, cost-effective, and environmentally friendly approach forAgNP biosynthesis using leaf extract of Psidiumguajavathat showed capping as well as reducing behaviour. Because of its well-known therapeutic benefits and the fact that it is freely available throughout the year and in all seasons, this plant was chosen for this study. They usedUV-vis and TEM experiments to confirm te AgNPs. The AgNPs' size was obtained in the 10-90 nm range. According to TEM results, the AgNPs were in spherical form. Green manufactured nanoparticles rendered from guava leaf extract can effectively suppress bacteria, according to their research.

Year 2016
The selected examples (year 2016) of antibacterial applications of biosynthesize AgNPs is given in antibacterial activity was found to be effective. The process is safe for the environment and presents no danger to it.

Year 2017
The selected examples (year 2017) of antibacterial applications of biosynthesize AgNPs is given in Table 3. The AgNPs were produced utilising a new eco-friendly synthesis approach that utilised Mangiferaindica leaves and were tested for antibacterial activity by D. Sundeep and co-workers. 44 According to the XRD peaks, the crystalline size of the bio-synthesized AgNPswas 32.4 nm. The antibacterial efficiency of the bio-source synthesised AgNPs was studied on E.coli and S.aureus, and the results explored that the AgNPs had potential antibacterial activity. S. Raja and colleagues 45 revealed that Calliandrahaematocephala leaf extract was used to successfully synthesise AgNPs. XRD was used to determine the crystalline nature and purity of AgNPs, revealing the presence of (111) and (220) lattice planes in the fcc structure of metallic silver. The antibacterial study against pathogenic E. coli bacteria yielded encouraging findings. J. Du and colleagues 46 reported on the production of AgNPs and their antibacterial activity using a soil-isolated bacterial strain, Novosphingobium sp. THG-C3. The synthesised AgNPs were shown spherical shape with the particle size from 8 to 25 nm. The XRD pattern revealed planes (111) Melissa officinal is was found to be capable of producing AgNPs with regulated properties and good inhibition of the bacteria used.

Year 2018
The selected examples (year 2018) of antibacterial applications of biosynthesize AgNPs is given in Table 4. M.P. Patil et al. 49 have devised a facile and environmentally friendly one-step synthesis of AgNPs employing Madhucalongifolia flower extract as a stabilising and reducing species. With a scale of 30-50 nm, the AgNPs were spherical and oval in shape. The presence of a brown colour in the reaction mixture is a main sign of AgNP production confirmed by a peak at 436 nm. The synthesised AgNPs were shown good potential E. coli, S. saprophyticus, B. cereus, S. typhimurium. The flower of M. longifolia was found as good source of AgNPs, which can be used as an antibacterial agent in therapeutics.Silver nitrate and methanolic root extract of Rhazyastricta, a member of the Apocynaceae family, were employed to synthesis AgNPs by A. Shehzad and colleagues. 50 The addition of xylitol to nanoparticles made them more stable and diffused. Aside from that, the plant extract and nanoparticles were tested for their antimicrobial properties against E. coli and B subtilis.The synthesised AgNPs had a diameter of 20 nm and a spherical form. AgNPs could be used in a number of environmental and medicinal applications. N. Sanchooli and colleagues 52 acquired AgNPs were gotten by combining silver nitrate and V. officinalis leaf separate. To characterise the synthesised AgNP, they used various analytical techniques. The antibiogramand lowest inhibitory concentration of the nanoparticles produced were determined using agar well diffusion and broth micro dilution, respectively. V. officinal is AgNPsshowed broad spectrum antibacterial action according to their findings.
M.E.T. Yazdi et al. 53 published their findings on the manufacture of AgNPs from Rheum turkestanicum aqueous shoot extract at room temperature, as well as antibacterial activity against human pathogenic bacteria. Biosynthesized AgNPs were observed to have prevalent antibacterial action against human pathogenic pathogens. Based on their findings, this process can be used to make large-scale preparations of other noble metals for a variety of purposes.

Year 2020
The selected examples (year 2019) of antibacterial applications of biosynthesize AgNPs is given in Table 6. M. Gomathi et al. 57 58 studied the environmentally friendly synthesis of AgNPs using Muntingiacalabura leaf extract as reducing and stabilising agents, as well as the antibacterial properties of the AgNPs generated. The generation of AgNPs was monitored using a UV-Vis spectrophotometer. The size and form of AgNPs were determined using TEM. The elemental analysis was interpreted using EDS. In a microbiological inhibition assay, muntingia leaf mediated AgNPs suppressed the development of Escherichia coli and Bacillus cereus, as shown by the existence of an inhibition region. The green synthesis of AgNPs as antibacterial agents was described by M.L. Guimares et al. 59 They used Ziziphusjoazeiro leaf extract as a green reaction medium for the production of AgNPs. At neutral pH, they obtained particles with a smaller size and a lower aggregation degree. S. aureus and E. coli were used to test the antibacterial activity. A. Nouri and colleagues 60 used Menthaaquatica leaf extract as a capping and reducing agent to synthesise ultra-small AgNPs utilising a green biogenic approach. Biosynthesized AgNPs were characterised using a variety of analytical techniques. Their findings showed that using ultrasound throughout the synthesis process can result in smaller AgNPs with improved antibacterial activity.

Conclusion
In summary, this review article addresses the antibacterial uses of biosynthesized AgNPs that were investigated between 2015 and 2020. AgNPs' antibacterial potential against a wide variety of microorganisms is discussed. AgNPs appear to be frequently used as an antibacterial agent against E.coli and S. aureus bacterial strains, according to our study.This review will be beneficial in the development of antibacterial agents based on biosynthesized AgNPs.