Nanozybiotics: Nanozyme-Based Antibacterials against Bacterial Resistance

Abstract

Infectious diseases caused by bacteria represent a global threat to human health. However, due to the abuse of antibiotics, drug-resistant bacteria have evolved rapidly and led to the failure of antibiotics treatment. Alternative antimicrobial strategies different to traditional antibiotics are urgently needed. Enzyme-based antibacterials (Enzybiotics) have gradually attracted interest owing to their advantages including high specificity, rapid mode-of-action, no resistance development, etc. However, due to their low stability, potential immunogenicity, and high cost of natural enzymes, enzybiotics have limitations in practical antibacterial therapy. In recent years, many nanomaterials with enzyme-like activities (Nanozymes) have been discovered as a new generation of artificial enzymes and perform catalytic antibacterial effects against bacterial resistance. To highlight the progress in this field of nanozyme-based antibacterials (Nanozybiotics), this review discussed the antibacterial mechanism of action of nanozybiotics with a comparison with enzybiotics. We propose that nanozybiotics may bear promising applications in antibacterial therapy, due to their high stability, rapid bacterial killing, biofilm elimination, and low cost.

Keywords: bacterial resistance; biofilm; enzybiotics; nanozybiotics; nanozymes.

Figure 1

Mechanisms of bacterial resistance. The figure shows a brief overview of intrinsic resistance mechanisms. Firstly, bacteria acquire drug-resistance through gene mutation at the genetic level. The mutated gene can also spread through vertical and horizontal transmission (herein, plasmid for example). Besides, biochemical mechanisms are a more common style of antidrug upon target change, efflux or inactivation. Moreover, the formation of biofilm prevents bacteria from reaching the antibiotic and enhances drug resistance.

Figure 2

Schematic of the antibacterial mechanism of several typical enzybiotics. (a) Schematic of the action of the lysozyme on Gram-positive and Gram-negative bacteria. (b) Proteinase can degrade proteins by hydrolyzing peptide bonds. (c) Nuclease mainly consists of DNase and RNase, which degrade DNA and RNA, respectively. This figure uses DNase hydrolysis of phosphodiester bound as an example. The black arrow is the hydrolysis site of DNase and the red arrow is the hydrolysis site of RNase (e.g., RNase A family).

Figure 3

Mechanisms of enzybiotics eradicating bacterial biofilm. The biofilm consists of a combination of glycoproteins, carbohydrates, lipids, eDNA, and bacterial cell. When treating with enzybiotics, different enzymes bind to their respective targets for degradation. In this figure, lysins, proteases and nucleases bind to polysaccharides, proteins and eDNA in the biofilm and degrade them, respectively, thus promoting the disintegration of the biofilm. Besides, lysins also decompose the peptidoglycan, one of the important components of bacteria cell walls, to kill bacteria, especially for Gram-positive species. The peptidoglycan of Gram-negative bacteria is difficult to degrade due to the protection of the outer membrane, while modified lysins may take effect.

Figure 4

Schematic illustration of the catalytic reaction and antibacterial (and antibiofilm) mechanism of nanozybiotics based on nanozymes with peroxidase- or oxidase-like enzyme activities. (a) Nanozymes with peroxidase-like activity catalyze the reduction of H₂O₂ and produce free ·OH. (b) Nanozymes with oxidase-like activity catalyze O₂ to ¹O₂, even single oxygen atoms. Both ·OH and ¹O₂ are strong oxidant, which oxidize the substrate (S) to ox-substrate (S_ox), for example, membrane lipid. (c) Nanozymes with peroxidase- or oxidase-like activity destroy the membrane structure or degrade the biofilm matrix to kill bacteria.

Figure 5

Schematic illustration of the antibacterial and antibiofilm mechanism of nanozybiotics based on nanozymes with deoxyribonuclease-like enzyme activities. Nanozymes with deoxyribonuclease activity catalyze the decomposition of DNA from dead bacteria to prevent the dissemination of released drug-resistant genes (a) and disperse the biofilm by decomposing the eDNA, the essential structural component of biofilm (b).

Figure 6

Schematic illustration of the antibacterial mechanism of combination therapy using nanozybiotics. Here, for example, nanozybiotics based on peroxidase (POD)-like nanozymes can catalyze the decomposition of hydrogen peroxide (H₂O₂) to produce bactericidal ·OH. With the radiation of light (visible or near-infrared light), photo-activated therapy (PTT and PDT) is active with excellent hyperthermia, singlet oxygen (¹O₂) and more ·OH production. The produced ·OH and ¹O₂ interact with bacteria to induce membrane peroxidation and damage cell integrity, making bacteria more vulnerable. In addition, the alternating magnetic field (AMF) exposure also can enhance the catalytic activity of nanozymes and generate more toxic ·OH.