Antibiotic resistance against infections caused by microbes has emerged as a global challenge resulting in longer hospitalizations and higher medical cost and mortality. The excessive use of antibiotics has led to the swift progression of antibiotic resistance in bacterial strains. Metallic and metal oxide (M/MO) nanoparticles (NPs) have the potential to provide a pertinent alternative to antibiotics as they interact with the critical cellular organelles and biomolecules such as DNA, enzymes, ribosomes, and lysosomes. This affects the permeability of the cell membrane causing oxidative stress, gene expression, protein activation, and enzyme activation restricting the habitat of microbes. Further, NPs simultaneously target multiple biomolecules at once making them an efficient antibacterial agent against which microbes are unable to develop resistance easily, although the toxicity associated with the M/MO NPs still remains a key challenge for clinical uses. Green synthesis provides an efficient solution to reduce the toxic effects associated with these NPs as it does not use harsh chemicals and environment for the synthesis of NPs. In this work, we have provided a comprehensive review of the green synthesis of M/MO NPs using plants (roots, seeds, barks, flowers) and microbes (bacteria, fungi, algae). The yield of the NPs achieved from the green synthesis is lower than that of conventional methods and significant advancements have been made recently which are delineated in this review for different M/ MO NPs. Further, the mechanism of NP interaction with the microbes and their different antimicrobial applications have been discussed in detailed. The present review aims to provide a critical overview of the current state of the large-scale synthesis of the M/ MO NPs as well as their different antimicrobial activities.

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Photo-microbes are well known to demolish rice and fruits, as farmers use chemical pesticides to overcome agricultural problems and economic damage. The use of pesticides in agriculture fails to protect crops in lower concentrations and increases the intake of chemicals that cause many human ailments. The sophisticated nanotechnology approach used in agriculture for antimicrobial activities offers several advantages for growth and improves nutrient absorption in plants. We report the green synthesis of silver nanoparticles (AgNPs) using Azadirachta indica (A. indica) and Mangifera indica (M. indica) tree leaf extract that contains antioxidants to treat numerous diseases. AgNPs tested against three plant pathogens, fungi Alternaria alternata (A. alternata), Sclerotium rolfsii (A. rolfsii), and bacteria Xanthomonas oryzae (X. oryzae), which leads to agricultural problems. The experiment was performed with different concentrations of AgNPs in μL/mL prepared using two other plants extract against fungi and bacteria during summer. The results expose the importance of plant extract in synthesizing silver nanoparticles (AgNPs) and their efficacy for microbes. A comparison among different concentrations of AgNPs (4 μL/mL, 6 μL/mL, and 10 μL/mL) was performed for two fungi (tomato disease) and bacteria (rice leaf blight disease). A-AgNPs (A. indica-AgNPs) demonstrate a greater zone of inhibition than M-AgNPs (M. indica-AgNPs), further highlighting the dependence of plants. Under in vitro conditions, the results of the antifungal activity showed zones of inhibition of 21 mm against A. alternata and 17 mm against A. rolfsii, while antibacterial activity against X. oryzae bacteria showed a 15 mm zone of inhibition at 10 mg/mL for A-AgNPs, and less for M-AgNPs. For AgNPs, the antifungal activity was characterized bya more significant area of inhibition than antibacterial activity was. The current study indicates that AgNPs with lower concentrations exhibitsuperior toxicity to microbes and may be able to manage diseases in rice and tomato, and increase plant growth.