Antibacterial Properties and Mechanisms of Action of Sonoenzymatically Synthesized Lignin-Based Nanoparticles

Abstract

In recent years, lignin has drawn increasing attention for different applications due to its intrinsic antibacterial and antioxidant properties, coupled with biodegradability and biocompatibility. However, chemical modification or combination with metals is usually required to increase its antimicrobial functionality and produce biobased added-value materials for applications wherein bacterial growth should be avoided, such as biomedical and food industries. In this work, a sonoenzymatic approach for the simultaneous functionalization and nanotransformation of lignin to prepare metal-free antibacterial phenolated lignin nanoparticles (PheLigNPs) is developed. The grafting of tannic acid, a natural phenolic compound, onto lignin was achieved by an environmentally friendly approach using laccase oxidation upon the application of high-intensity ultrasound to rearrange lignin into NPs. PheLigNPs presented higher antibacterial activity than nonfunctionalized LigNPs and phenolated lignin in the bulk form, indicating the contribution of both the phenolic content and the nanosize to the antibacterial activity. Studies on the antibacterial mode of action showed that bacteria in contact with the functionalized NPs presented decreased metabolic activity and high levels of reactive oxygen species (ROS). Moreover, PheLigNPs demonstrated affinity to the bacterial surface and the ability to cause membrane destabilization. Antimicrobial resistance studies showed that the NPs did not induce resistance in pathogenic bacteria, unlike traditional antibiotics.

Antibacterial lignin-based nanoparticles and their use in composite materials

“…3a(iii)). 69 The inhibitory capacity of phenolated lignin particles (PheLigNPs) against Gram-positive and Gram-negative bacteria was higher in comparison with that of bulk lignin, phenolated bulk lignin, and non-phenolated LigNPs. This demonstrated the contribution of both the nanosize and the phenolic content in the antibacterial activity of lignin.…”

“…Spherical particles are commonly obtained from solvent displacement methods, 65–67 while acid treatment and ultrasonication yield irregular-shaped particles. 64,68–70…”

“…81 This is in agreement with other studies reporting a decrease in metabolic activity of bacteria in the presence of subinhibitory concentrations of LigNPs. 69 Moreover, it has been demonstrated that LigNPs, due to their hydrophobic nature, can intercalate with the lipids of the bacterial envelope, causing a membrane disturbing effect. 69 The antibacterial mode of action of LigNPs also increases oxidative stress by inducing ROS generation.…”

“…69 Moreover, it has been demonstrated that LigNPs, due to their hydrophobic nature, can intercalate with the lipids of the bacterial envelope, causing a membrane disturbing effect. 69 The antibacterial mode of action of LigNPs also increases oxidative stress by inducing ROS generation. 69,82 Based on the reports summarized above, the mode of action of LigNPs would combine (1) penetration inside the cell resulting in increased levels of oxidative stress and decreased metabolic activity, and (2) adherence to bacterial cells and intercalation into the membrane, which eventually causes cell lysis (Fig.…”

Advances in the screening of antimicrobial compounds using electrochemical biosensors: is there room for nanomaterials?

“…Their superior qualities have also made them ideal candidates as promising antimicrobial drugs [ 81 , 82 ]. With silver nanoparticles (AgNPs) showing up for their intrinsic antimicrobial properties against known bacterial strains such as E. coli , S. aureus , or P. aeruginosa , multimetallic nanoparticles have also seem to be effective [ 83 ].…”