Sublethal Concentrations of Silver Nanoparticles Stimulate Biofilm Development

Abstract

Although silver nanoparticles (AgNPs) are used as antimicrobial agents in a wide variety of commercial products, sublethal exposure can counterproductively promote the development of biofilms. We observed by fluorescence microscopy denser biofilm growth with mixed cultures from a wastewater treatment plant after exposure to 21.6 μg/L 10 nm AgNPs. To further understand biofilm promotion mechanisms, experiments were conducted with a pure culture of Pseudomonas aeruginosa PAO1. Sublethal exposure of PAO1 to AgNPs (10.8 and 21.6 μg/L) also enhanced biofilm development and upregulated quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance (efflux pump) genes. An increase in the sugar and protein contents of the PAO1 biofilm matrix (by 55 ± 3 and 114 ± 32%, respectively, relative to unexposed controls) corroborated the transcriptional upregulation of PAO1 biofilm-related genes. Enhanced biofilm development by exposure to low AgNP concentrations might accelerate biofouling and biocorrosion and harbor pathogens that pose a risk to public health.

Inhibition of bacterial surface colonization by immobilized silver nanoparticles depends critically on the planktonic bacterial concentration

“…This suggests that P. fluorescens bacteria respond to the silver stress by forming biofilms, even though in the current situation the source of the stress is the silver ion released from the AgNPs that are adsorbed on the substrate. This supports the recent report that exposure to sublethal concentrations of suspended AgNPs stimulates biofilm development [49]. Since this high biofilm coverage is observed on both the uncoated and coated regions of the same coverslip, it must result from dissolved silver effects.…”

“…The inoculum concentration controls the silver to biomass ratio in the system. The importance of this ratio is also indicated by recent evidence that exposure to sublethal concentrations of suspended AgNPs stimulates biofilm formation, perhaps as an environmental stress response [49]. The effect of inoculum concentration on the anti-colonization performance of silver-laden surfaces must be considered explicitly, both for antifouling surface engineering and for understanding the environmental implications of AgNPs.…”

Effects of sublethal concentrations of silver nanoparticles on Escherichia coli and Bacillus subtilis under aerobic and anaerobic conditions

“…[34][35][36] By contrast, 1 lg/ml AgNPs promoted adhesion in B. subtilis under aerobic conditions, the same condition that increased the MSGR in the planktonic growth tests. Recently, Yang and Alvarez 15 reported that sublethal exposure of Pseudomonas aeruginosa PAO1 to AgNP enhanced biofilm development and upregulated quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance (efflux pump) genes.…”

“…[11][12][13] Indeed, predicted environmental concentrations of AgNPs ranging from 1 pg/ml to 10 lg/ml have been found in both solid and liquid environmental matrixes. 14,[57][58][59] To the best of our knowledge, only a few scientific works have investigated the effects of sublethal AgNP concentrations on microbial systems; [15][16][17] therefore, their impact on microbial physiology and behavior still remains almost unknown. Moreover, despite the growing body of literature regarding nanoparticles in biosolids, [51][52][53] little is known about the effects of sublethal concentrations of AgNPs on anaerobic ecosystems.…”

Modeling Biofilms in Water Systems with New Variables: A Review

“…For instance, the silver nanoparticles (AgNPs) showed promising antimicrobial activity on various microbial strains [80]. Recently, Yang et al [81] discovered that the sublethal concentrations of AgNPs promoted the formation of biofilms by P. aeruginosa via upregulating a complex genetic networks associated with QS, EPS, as well as the antibiotic resistance genes. Upadhyayulaa and Gadhamshettyb [82] reported that the carbon nanotubes and their composites possess the capability of inducing biofilm formation as well at low level concentrations as well, while they were traditionally regarded as antimicrobial materials.…”