An overview of the plant-mediated green synthesis of noble metal nanoparticles for antibacterial applications

Inorganic Nanoparticles and Composite Films for Antimicrobial Therapies

“…While there are many studies demonstrating the intrinsic antibacterial and antifungal properties of AuNPs, their effects are still ambiguous [ 73 , 74 ]. Reports have suggested that the mechanisms involved in the antimicrobial effects of AuNPs include interactions between NPs and the microbial cell wall governed by electrostatic forces and carbohydrate, lipid, and protein binding; damages of the microbial cell membrane and wall and subsequent ribosome and mitochondrion impairment; and inhibition of thiol groups present within bacterial cells [ 73 , 74 , 75 ].…”

“…While there are many studies demonstrating the intrinsic antibacterial and antifungal properties of AuNPs, their effects are still ambiguous [ 73 , 74 ]. Reports have suggested that the mechanisms involved in the antimicrobial effects of AuNPs include interactions between NPs and the microbial cell wall governed by electrostatic forces and carbohydrate, lipid, and protein binding; damages of the microbial cell membrane and wall and subsequent ribosome and mitochondrion impairment; and inhibition of thiol groups present within bacterial cells [ 73 , 74 , 75 ]. Other specific antimicrobial activities might include vesicle formation and the subsequent production of membrane holes in E. coli and C. pseudotuberculosis , intracellular ROS concentration increase in S. aureus , transcription inhibition in S. aureus and E. coli , and inclusion body formation and subsequent bacterial cell lysis in S. pneumoniae [ 75 , 76 ].…”

“…Furthermore, AuNPs interact with the negatively charged teichoic acids highly abundant within the cell wall of Gram-positive bacteria and the lipopolysaccharides present onto the outer membrane of Gram-negative bacteria [ 74 ]. It was observed that AuNPs exhibit higher antibacterial activity against Gram-negative bacteria, possibly due to a reduced cell wall thickness and more stable electrostatic interactions [ 73 ]. By binding to the proteins present onto the surface and further inhibiting their attachment to the receptors found within the host cells, AuNPs have also proven their efficiency against many viruses, including measles virus, Newcastle disease virus, respiratory syncytial virus, and chikungunya virus [ 74 ].…”

“…While their efficiency has been proven against more than 650 microorganisms, including Gram-positive and Gram-negative bacteria, fungi, and viruses, the precise mechanism of action of AgNPs is still not completely elucidated [ 82 , 83 ]. The primary mechanism is based on the interaction between the positively charged AgNPs and the negatively charged plasma cell membranes, which further results in the accumulation within the membrane and the consequent structural modifications and permeabilization due to cis-trans isomerization of the unsaturated membrane fatty acids [ 73 , 80 , 82 , 84 ]. In this manner, Ag + is released from the outer surface of the NP, thus interacting with nucleic acids and proteins and further generating high amounts of ROS, namely, singlet oxygen, hypochlorous acid, hydroxyl radical, superoxide anion, and hydrogen peroxide [ 73 , 80 , 82 , 83 ].…”

“…In this manner, the enzyme is unable to perform its functions, thus causing cell or organism death [ 82 ]. Similar to AuNPs, AgNPs have proven higher efficiency towards Gram-negative bacteria due to a reduced cell wall thickness and an increased number of negative charges [ 73 , 84 ]. In the case of fungi, AgNPs interfere with the cell metabolism through the generation of ROS and modification of ergosterol levels and lead to cell lysis.…”