Gold Nanoparticles with Antibiotic-Metallopolymers toward Broad-Spectrum Antibacterial Effects

Abstract

Bacterial infection has evolved into one of the most dangerous global health crises. Designing potent antimicrobial agents that can combat drug-resistant bacteria is essential for treating bacterial infections. In this paper, a strategy to graft metallopolymer-antibiotic bioconjugates on gold nanoparticles is developed as an antibacterial agent to fight against different bacterial strains. Thus, these nanoparticle conjugates combine various components in one system to display enhanced bactericidal efficacy, in which small sized nanoparticles provide high surface area for bacteria to contact, cationic metallopolymers interact with the negatively charged bacterial membranes, and the β-lactam antibiotics' sterilzation capabilities are improved via evading intracellular enzymolysis by β-lactamase. This nanoparticle-based antibiotic-metallopolymer system exhibits an excellent broad-spectrum antibacterial effect, particularly for Gram-negative bacteria, due to the synergistic effect of multicomponents on the interaction with bacteria.

Keywords: antibiotics; antimicrobial; cobaltocenium; gold nanoparticles; metallopolymers.

Figure 1.

TEM images of a) Au NPs, b) Au@PCo-6K, c) Au@PCo-15K, and d) Au@PCo-30K.

Figure 2.

a) Agar diffusion Disk-diffusion assays of penicillin-G, PCo-Peni conjugates and Au@PCo-Peni NPs against (i) S.aureus, (i)E. coli, (i) K. pneumonia, and (iv) P. vulgaris. 30 μL aqueous solution of antimicrobial agents with different weights (5-15 μg) was dropwise added to disks, and the culture dishes were incubated in the oven for 18 h at 28 °C. b) OD₆₀₀ values and c) inhibitory percentage of four bacteria incubated with penicillin-G, PCo-Peni and Au@PCo-Peni NPs, respectively. The tryptic soy broth (TSB) solutions of four different bacteria without any antimicrobial agents were used as the control groups. The 96-well plates were cultured shakily for 12 hours at 37 °C.

Figure 3.

a) Confocal laser scanning microscopy (CLSM) images and b) scanning electron microscopy (SEM) images of control groups and Au@PCo-Peni NPs against four different bacteria. The concentration of Au@PCo-Peni NPs was 18.5 μg/mL, based on the effective penicillin-G concentration (5 μg/mL) in Au@PCo-Peni NPs. The concentration of bacteria was 1.0×10⁶ CFU/mL. For CLSM images, LIVE/DEAD BacLight dye (Bacterial Viability Kit; Invitrogen Inc.) was used to stain the bacteria and check bacteria viability. Green color indicated live bacteria; yellow or red color indicated dead bacteria. For SEM images, all scale bars are 2 μm.

Figure 4.

TEM images of the control and Au@PCo-Peni NPs against S. aureus and E. coli. The concentration of Au@PCo-Peni NPs was 18.5 μg/mL, based on the effective penicillin-G concentration (5 μg/mL) in Au@PCo-Peni NPs. The concentration of bacteria was 1.0×10⁶ CFU/mL. All scale bars are 1 μm.

Scheme 1.

a) Synthesis of cationic thiol end-capped cobaltocenium homopolymers by RAFT polymerization and dithioester reduction. b) Synthesis of antimicrobial Au@PCo-Peni nanoparticles by a “grafting-to” approach and a bioconjugation between cationic PCo and anionic β-lactam antibiotic Penicillin-G.