Engineering nanoparticles to silence bacterial communication

Abstract

The alarming spread of bacterial resistance to traditional antibiotics has warranted the study of alternative antimicrobial agents. Quorum sensing (QS) is a chemical cell-to-cell communication mechanism utilized by bacteria to coordinate group behaviors and establish infections. QS is integral to bacterial survival, and therefore provides a unique target for antimicrobial therapy. In this study, silicon dioxide nanoparticles (Si-NP) were engineered to target the signaling molecules [i.e., acylhomoserine lactones (HSLs)] used for QS in order to halt bacterial communication. Specifically, when Si-NP were surface functionalized with β-cyclodextrin (β-CD), then added to cultures of bacteria (Vibrio fischeri), whose luminous output depends upon HSL-mediated QS, the cell-to-cell communication was dramatically reduced. Reductions in luminescence were further verified by quantitative polymerase chain reaction (qPCR) analyses of luminescence genes. Binding of HSLs to Si-NPs was examined using nuclear magnetic resonance (NMR) spectroscopy. The results indicated that by delivering high concentrations of engineered NPs with associated quenching compounds, the chemical signals were removed from the immediate bacterial environment. In actively-metabolizing cultures, this treatment blocked the ability of bacteria to communicate and regulate QS, effectively silencing and isolating the cells. Si-NPs provide a scaffold and critical stepping-stone for more pointed developments in antimicrobial therapy, especially with regard to QS-a target that will reduce resistance pressures imposed by traditional antibiotics.

Keywords: nanomedicine; nanoparticles; quorum quenching; quorum sensing.

Figure 1

Schematic of β-cyclodextrin coated silicon dioxide nanoparticle.

Figure 2

Schematic of nanoparticle-based silencing of bacterial quorum sensing (QS). (A) Diagram of the Gram-negative bacterium Vibrio fischeri lux operon used in luminescence during QS using acyl-homoserine lactones (HSL). Triangles represent 3OC6-HSL. LuxR/3OC6-HSL complex initiates bilateral transcription of lux operon. LuxI produces 3OC6-HSL. Inset: A one-liter V. fischeri culture flask luminescing after treatment with HSLs. (B) Diagram of V. fischeri during nanoparticle treatment. Binding of HSLs by Si-NPs quenches QS and subsequent gene expression in lux. (C) Changes in maximum bioluminescence by V. fischeri during exposure to 2 μ M 3OC6-HSL, with either β-CD or β-CD functionalized Si-NPs. Error bars represent standard error of the mean (n = 3). Asterisks indicate significance (P = 0.05) by ANOVA.

Figure 3

Mean relative maximum bioluminescence per OD (600 nm) of V. fischeri during exposure to 125 nM 3OC6-HSL and 0.25 nM C8-HSL treated with 250 nM β-CD, bare 15 nm Si-NPs, 155 nM β-CD functionalized 15 nm Si-NPs, bare 50 nm Si-NPs, or 133 nM β-CD functionalized 50 nm Si-NPs. Error bars represent standard error of the mean (n = 3). Asterisks indicate significance (P = 0.05).