Silver nanoparticles exert concentration-dependent influences on biofilm development and architecture.

Jingyang Guo,Min Lv,Simin Qin,Hongzhen Peng,Shima Liu,Qingnuan Li,Yan Wei,Liqiang Luo

doi:10.1111/cpr.12616

Abstract

ObjectivesTo investigate the impact of silver nanoparticles (AgNPs) on the biofilm growth and architecture.Materials and methodsSilver nitrate was reduced by d‐maltose to prepare AgNPs in the presence of ammonia and sodium hydroxide. The physicochemical properties of AgNPs were characterized by transmission electron microscopy, ultraviolet‐visible spectroscopy and inductively coupled plasma mass spectrometry. The development of biofilm with and without AgNPs was explored by crystal violet stain. The structures of mature biofilm were visually studied by confocal laser scanning microscopy and scanning electron microscopy. Bacterial cell, polysaccharide and protein within biofilm were assessed quantitatively by colony‐counting method, phenol‐sulphuric acid method and Bradford assay, respectively.ResultsThe spherical AgNPs (about 30 nm) were successfully synthesized. The effect of AgNPs on Pseudomonas aeruginosa biofilm development was concentration‐dependent. Biofilm was more resistant to AgNPs than planktonic cells. Low doses of AgNPs exposure remarkably delayed the growth cycle of biofilm, whereas high concentration (18 μg/mL) of AgNPs fully prevented biofilm development. The analysis of biofilm architecture at the mature stage demonstrated that AgNPs exposure at all concentration led to significant decrease of cell viability within treated biofilms. However, sublethal doses of AgNPs increased the production of both polysaccharide and protein compared to control, which significantly changed the biofilm structure.ConclusionsAgNPs exert concentration‐dependent influences on biofilm development and structure, which provides new insight into the role of concentration played in the interaction between antibacterial nanoparticles and biofilm, especially, an ignored sublethal concentration associated with potential unintended consequences.

Highlights

Antimicrobial resistance (AMR) has gained considerable attentions due to its serious threat for public health and environmental safety.[1,2] Biofilm is considered to be the most important cause of bacterial resistance except for well‐known super‐bacteria induced by antibiotics abuse.[3-5]
The antibacterial nanoparticles are considered as promising candidates for addressing AMR,[19,48] multiple cycles of treatment below lethal concentration led to gradual increases in minimum inhibitory concentration (MIC) of AgNPs,[36] which exacerbates our concerns about whether biofilm exhibits tolerance and resistance to it
This work reported the concentration‐dependent impact of AgNPs on the development of P aeruginosa biofilm, especially, an ignored potential unintended result associated with bacterial exposure to sublethal concentrations of AgNPs

Summary

Introduction

Antimicrobial resistance (AMR) has gained considerable attentions due to its serious threat for public health and environmental safety.[1,2] Biofilm is considered to be the most important cause of bacterial resistance except for well‐known super‐bacteria induced by antibiotics abuse.[3-5]. Biofilm is the surface‐associated bacterial community integrated by microbial cells and self‐secreted extracellular polymeric substances (EPS),[6-8] showing 10‐1000 times more resistant to traditional bactericides (eg, antibiotics and heavy metal ions) than planktonic cells.[9,10]. This ubiquitous AMR system is extremely difficult to eliminate in clinic, industry and environment, which has given rise to serious infection and economic loss.[1,11]. Some of them with specific optical and thermal properties can be exploited to inhibit the bacterial growth by selective non‐invasive photothermic destroy.[5] These characteristics of nanomaterials different from conventional antimicrobials provide new insights into the prevention of biofilm formation and even eradication of formed biofilm.[21]

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