Recent Advancements in Plant- and Microbe-Mediated Synthesis of Metal and Metal Oxide Nanomaterials and Their Emerging Antimicrobial Applications

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.