Iron oxide nanoparticle-mediated hyperthermia stimulates dispersal in bacterial biofilms and enhances antibiotic efficacy.

Thuy-Khanh Nguyen,Ramona Selvanayagam,Nicolas Barraud,Hien T T Duong,Cyrille Boyer

doi:10.1038/srep18385

Abstract

The dispersal phase that completes the biofilm lifecycle is of particular interest for its potential to remove recalcitrant, antimicrobial tolerant biofilm infections. Here we found that temperature is a cue for biofilm dispersal and a rise by 5 °C or more can induce the detachment of Pseudomonas aeruginosa biofilms. Temperature upshifts were found to decrease biofilm biomass and increase the number of viable freely suspended cells. The dispersal response appeared to involve the secondary messenger cyclic di-GMP, which is central to a genetic network governing motile to sessile transitions in bacteria. Furthermore, we used poly((oligo(ethylene glycol) methyl ether acrylate)-block-poly(monoacryloxy ethyl phosphate)-stabilized iron oxide nanoparticles (POEGA-b-PMAEP@IONPs) to induce local hyperthermia in established biofilms upon exposure to a magnetic field. POEGA-b-PMAEP@IONPs were non-toxic to bacteria and when heated induced the detachment of biofilm cells. Finally, combined treatments of POEGA-b-PMAEP@IONPs and the antibiotic gentamicin reduced by 2-log the number of colony-forming units in both biofilm and planktonic phases after 20 min, which represent a 3.2- and 4.1-fold increase in the efficacy against planktonic and biofilm cells, respectively, compared to gentamicin alone. The use of iron oxide nanoparticles to disperse biofilms may find broad applications across a range of clinical and industrial settings.

Highlights

The dispersal phase that completes the biofilm lifecycle is of particular interest for its potential to remove recalcitrant, antimicrobial tolerant biofilm infections
When the temperature was reduced from 30 °C to 25 °C or from 37 °C to 25 °C or 15 °C, the amount of biomass released in the effluent appeared to decrease as seen by a reduction of 45% to 55% in OD600 measurements, suggesting that basal, non-specific cell detachment was inhibited upon temperature downshift (Fig. 1A)
Taken together these data strongly suggest that hyperthermia associated with an increase in temperature is a potent signal for biofilm dispersal

Summary

Introduction

The dispersal phase that completes the biofilm lifecycle is of particular interest for its potential to remove recalcitrant, antimicrobial tolerant biofilm infections. Recent studies have shown that biofilm dispersal can be induced in response to a range of environmental cues including changes in the availability of nutrients such as carbon sources[8,9] or oxygen (O2)[10], low levels of nitric oxide (NO)[11] or iron levels[12], as well as several bacterially derived signals including quorum sensing (QS) acyl-homoserine lactones[13], autoinducing peptides[14] and diffusible fatty acids[15,16]. C-di-GMP is the central element of a complex regulatory network that includes sensor and effector proteins and controls the transition between planktonic and biofilm lifestyles[17] Via this network, environmental cues and signals can stimulate enzymes that modify intracellular levels of c-di-GMP, which in turn regulates a range of downstream effectors leading to biofilm formation or dispersal. Decreases in temperature from 37 °C to 25 °C or 15 °C were found to trigger an increase in intracellular levels of c-di-GMP and increased biofilm biomass, and a mutant lacking 6 DGC-encoding genes did not form biofilms in response to a temperature downshift[22]

Methods

Results

Conclusion